ArticlePDF AvailableLiterature Review

Oviductal secretions: Will they be key factors for the future ARTs?

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  • Spanish National Research Council, Spain

Abstract and Figures

A variety of evolutionary processes has led to the development of different organs to ensure that internal fertilization occur successfully. Fallopian tubes are a particularly interesting example of such organs. Some of the key events during fertilization and early embryo development occur in the oviduct. Knowledge of the different components described in the oviduct is extensive. Oviductal components include hormones, growth factors and their receptors that have important roles in the physiology of the oviduct and embryo development. Other oviductal factors protect the gamete and the embryos against oxidative stress and pathogens. Different proteins and enzymes are present in the oviductal fluid and have the ability to interact with the oocyte and the sperm before the fertilization occurs. Of special interest is the oviduct-specific glycoprotein (OVGP1), a glycoprotein that is conserved in different mammals, and its association with the zona pellucida (ZP). Interaction of the oocyte with oviductal secretions leads us to emphasize the concept of 'ZP maturation' within the oviduct. The ZP changes produced in the oviduct result in an increased efficiency of the in vitro fertilization technique in some animal models, contributing in particular to the control of polyspermy and suggesting that a similar role could be played by oviductal factors in human beings. Finally, attention should be given to the presence in the oviductal fluid of several embryotrophic factors and their importance in relation to the in vivo versus in vitro developmental ability of the embryos.
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NEW RESEARCH HORIZON Review
Oviductal secretions: will they be key
factors for the future ARTs?
Manuel Avile
´s1,*, Alfonso Gutie
´rrez-Ada
´n2, and Pilar Coy3
1
Department of Cell Biology and Histology, Faculty of Medicine, University of Murcia, Murcia, Spain
2
Department of Animal Reproduction,
INIA, Madrid, Spain
3
Department of Physiology, Veterinary Faculty, University of Murcia, Murcia, Spain
*Correspondence address. Tel: +34-868884385; Fax: +34-868884323; E-mail: maviles@um.es
Submitted on May 31, 2010; resubmitted on June 16, 2010; accepted on June 22, 2010
abstract: A variety of evolutionary processes has led to the development of different organs to ensure that internal fertilization occur
successfully. Fallopian tubes are a particularly interesting example of such organs. Some of the key events during fertilization and early embryo
development occur in the oviduct. Knowledge of the different components described in the oviduct is extensive. Oviductal components
include hormones, growth factors and their receptors that have important roles in the physiology of the oviduct and embryo development.
Other oviductal factors protect the gamete and the embryos against oxidative stress and pathogens. Different proteins and enzymes are
present in the oviductal fluid and have the ability to interact with the oocyte and the sperm before the fertilization occurs. Of special interest
is the oviduct-specific glycoprotein (OVGP1), a glycoprotein that is conserved in different mammals, and its association with the zona pel-
lucida (ZP). Interaction of the oocyte with oviductal secretions leads us to emphasize the concept of ‘ZP maturation’ within the oviduct. The
ZP changes produced in the oviduct result in an increased efficiency of the in vitro fertilization technique in some animal models, contributing
in particular to the control of polyspermy and suggesting that a similar role could be played by oviductal factors in human beings. Finally,
attention should be given to the presence in the oviductal fluid of several embryotrophic factors and their importance in relation to the
in vivo versus in vitro developmental ability of the embryos.
Key words: oviduct-specific glycoprotein / concept of zona pellucida maturation / oviductal secretions / in vitro development / embryo-
trophic factors
Introduction
In sexual reproduction, whereby male and female give rise to different
gametes that must meet and fuse to produce a new organism, two
principal strategies have been developed: external and internal fertili-
zation. In the external fertilization model, large numbers of both
gametes are usually released into the external aquatic milieu. In the
internal fertilization model, the male has developed a specific organ
that allows the introduction of the sperm into the female genital
tract during copulation. Moreover, different evolutionary processes
have led to the development of different organs to ensure that fertili-
zation takes place and that the embryo develops. Fallopian tubes in
primates, usually named oviducts in non-primates, are a particular
example of such organs, although their specific role in fertilization is
controversial. Although Fallopian tubes have long been considered a
mere conduit for gametes and embryos, numerous studies performed
during recent decades have demonstrated that the oviduct is involved
in several important processes (gamete maturation, capacitation,
sperm selection, embryo development etc.) that are necessary for
the appropriate gamete and embryo physiology (Hunter, 1998).
Later, we will focus on some oviductal processes recently described
in mammalian species other than humans that contribute to optimal
fertilization and early embryo development. These findings could
provide useful information for the development of new strategies to
improve some of the assisted reproductive techniques currently
used in humans.
Oviductal fluid composition
The oviductal secretion is a complex fluid formed by secreted com-
ponents from epithelial cells and from blood plasma. It contains
many metabolic components, including glucose, lactate, pyruvate
and amino acids, whose respective concentrations often differ from
those of the uterine fluid and plasma (Stanke et al., 1974;Gardner
et al., 1996;Tay et al., 1997;Aguilar and Reyle, 2005;Harris et al.,
2005;Li et al., 2007;Hugentobler et al., 2008;Leese et al., 2008;
Vecchio et al., 2009;Hugentobler et al., 2010). A large number of pro-
teins have been detected in oviduct and/or oviductal secretion, and
the list of components is growing each year (Supplementary Table
S1; Buhi et al., 2000;Killian, 2004;Georgiou et al., 2007). It was
reported that some of these components influence or may contribute
to the optimal development of the different processes that take place
in the oviduct. Readers are directed to the different references
included in Supplementary Table S1 for detailed information on the
&The Author 2010. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved.
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role played by these oviductal components. Thus, the components
can be classified in different groups as: (i) growth factors, cytokines
and receptors, (ii) hormones and receptors, (iii) proteases and inhibi-
tors, (iv) antioxidant protective agents, (v) defense agents, (vi) glyco-
sidases and glycosyl transferases, (vii) other enzymes, (viii) chaperones
and heat shock proteins, (ix) other proteins, (x) glycosaminoglycans
and proteoglycans and (xi) other components. It was reported that
growth factors produced by oviductal epithelium contribute to more
efficient embryo development (this aspect is reviewed in more
detail later in this manuscript). Other oviductal components are
responsible for the protection of gametes and embryos against oxi-
dative stress. It is known that sperm are damaged by reactive
oxygen species (Aitken and De Iuliis, 2010). Glycosidases are
present in the epididymal fluid and contribute to sperm maturation
(Tulsiani et al., 1998;Tulsiani, 2006). Glycosidases have been detected
in the oviductal fluid of different species (Supplementary Table S1).
Therefore, a similar change in the carbohydrates of the sperm
plasma membrane could be anticipated in the oviduct; however, this
effect and its significance require further studies. These enzymes
have the ability to modify the glycoproteins contained in the zona pel-
lucida (ZP), membrane of the epithelial cells and sperm, and conse-
quently these enzymes could affect the sperm binding to the ZP and
to the oviduct. Recently, we observed that oviductal fluid exhibits gly-
cosidase activity with specific variations during the estrous cycle,
suggesting a specific role in the regulation of the carbohydrate residues
present in the oviduct and gametes (Carrasco et al., 2008a,b). Some
proteins or glycoproteins have been observed to bind to the sperm or
the oocyte as osteopontin, glycodelin and oviduct-specific glyco-
protein (OVGP1), modifying the gamete physiology and the fertiliza-
tion (Gabler et al., 2003;Chiu et al., 2007;Coy et al., 2008).
Precise information about the different proteins contained in ovi-
ductal fluid is lacking, especially in the case of humans, where obtaining
biological samples is more difficult. However, thanks to microarray
analysis, extensive information about gene expression in human ovi-
ductal mucosa was recently made available, providing a more accurate
idea of the probable protein composition of the oviductal fluid (Tone
et al., 2008). Previously, an analysis of the gene expression in bovine
oviductal epithelial cells at estrus and diestrus was performed
showing differential gene expression (37 up-regulated at estrus and
40 at diestrus) between them (Bauersachs et al., 2004). The oocyte,
sperm and embryos are present in the oviduct at different times
(cycle phases) and in different places, suggesting that the composition
of oviductal fluid is dynamically changing: for example, a different func-
tion was observed for the oviductal fluid obtained from the ampulla
than from the isthmus (Way et al., 1997). As another example, it is
important to take into consideration that the oviductal secretion
could be modified by the presence of gametes, as it was recently
shown in in vitro (Kodithuwakku et al., 2007) and in vivo studies (Geor-
giou et al., 2007). Future improvements and increased efficiency of the
analytical methods used will allow the analysis of different samples col-
lected in low amounts and provide detailed information on the genes
transcribed and proteins secreted in the oviduct in different physiologi-
cal conditions and in different anatomical regions. These studies will
probably be performed in animal models in the first instance due to
the difficulty of collecting samples in humans. Such developments
will throw more light on the fertilization and embryo development
processes. Additionally, in order to clarify the role played by the
different proteins, it will be necessary not only to purify them but
also to perform assays in a context that mimics as closely as possible
the in vivo situation. In the following paragraphs, we will describe some
of the recent findings in this field with special focus on OVGP1.
Oviduct-specific glycoprotein
OVGP1 belongs to the glycosyl hydrolase 18 family, which includes
proteins with chitin-hydrolyzing activity; however, no enzymatic
activity has been described for this oviductal protein (DeSouza and
Murray, 1995;Buhi et al., 1996;Jaffe et al., 1996). OVGP1 was detected
in the genome of different mammals including monotremes (Warren
et al., 2008), marsupials (Mikkelsen et al., 2007) and placentals. The
protein expressed by the OVGP1 gene, known as OVGP1, is also
named oviductin or mucin-9 and has been identified in several placen-
tal species, including human (Donnelly et al., 1991;Arias et al., 1994;
Sendai et al., 1994,1995;DeSouza and Murray, 1995;Suzuki et al.,
1995;Buhi et al., 1996;Verhage et al., 1997;Buhi, 2002;Killian,
2004). However, it was recently reported that horses and rats are
special cases because OVGP1 homolog is a pseudogene and conse-
quently this protein is not expressed by the oviduct (Mugnier et al.,
2009;Tian et al., 2009). The facts that the OVGP1 is not expressed
in these species and that OVGP1 gene-null mice has apparently a
normal fertility (Araki et al., 2003) suggest that the role played by
this glycoprotein is not essential for fertilization in some species.
Maximum production of OVGP1 is dependent on the plasma estro-
gen level in cows, baboon, sheep, pig and human (Arias et al., 1994;
DeSouza and Murray, 1995;Buhi et al., 1996;Verhage et al., 1997;
Lok et al., 2002); however, no difference in mRNA expression was
observed in the hamster or rabbit oviduct during the estrous cycle
(Paquette et al., 1995;Merchan et al., 2007). OVGP1 shows different
amino acid lengths among species (Fig. 1). Additionally, OVGP1 poly-
morphism has been reported in hamster and rabbit (Merchan et al.,
2007;Paquette et al., 1995). This polymorphism can also be seen in
human, mouse and sheep when the databases were analyzed. A com-
parative analysis of the similarities in the amino acid sequences of
different species points to a high degree of conservation in the N-
terminal region of the protein (Verhage et al., 1997). In contrast, con-
siderable divergence has been observed in the C-terminal region of
the protein (Fig. 1); however, little information about the biological
role played by the C-terminal region exists (Yong et al., 2002).
Thus, Yong et al. (2002) have reported that the C-terminal region
of the OVGP1 protein seems to be responsible for overcoming the
2-cell embryo blockage in rabbits. The future use of recombinant-
protein technology capable of producing native forms, truncated and
chimera proteins would probably provide important information
about these different regions of the proteins.
Gamete interactions with
oviductal secretions: oocyte
and ZP maturation
Oviduct and its secretion affect the physiology of the gametes. Capaci-
tation, selection and storage of the sperm during its transit in the oviduct
have been analyzed in detail previously (reviewed in Yanagimachi, 1994;
Suarez, 2007;Suarez, 2008a,b;Talevi and Gualtieri, 2010). For that
reason, this aspect will not be addressed in this review. We will focus
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on other aspects, such as the effect of the oviductal secretions in the
oocyte and embryo development.
Oocyte development occurs in the ovary during the follicle growth
(folliculogenesis), during that time many changes take place. Previous
studies showed that ZP properties are modified during folliculogenesis
in several species including humans (Tesarik et al., 1988;Oehninger
et al., 1991;Avile
´set al., 1999,2000a,b). These changes have been
collectively referred to as zona maturation (Fig. 2). However, little
attention has been paid in the literature to the changes produced in
the ZP after ovulation. This is mainly due to the difficulty in obtaining
these tubal oocytes, especially in species such as human, bovine and
porcine. Although ovarian oocytes can be fertilized, they are not
exactly the same as their in vivo counterparts. Several studies have
reported that the extracellular oocyte coat is modified after ovulation
during its transit through the oviduct (Oikawa et al., 1988;Robitaille
et al., 1988;Kolbe and Holtz, 2005;Lyng and Shur, 2009). Some of
these changes have been shown to be necessary and affect sperm–
ZP binding as well as the role of the ZP in the control of polyspermy.
Zona maturation and spermZP binding
It has been more than 20 years since the description of how the
hamster ZP is modified by an oviductal factor (Robitaille et al.,
1988) and how this factor could be involved in fertilization (Sakai
et al., 1988;Boatman and Magnoni, 1995). OVGP1s associated with
the ZP of ovarian oocytes after ovulation in several species. In
humans, there is no direct in vivo evidence for any association of the
OVGP1 and the ovulated oocyte. An indirect approach using in vitro
Figure 1 Alignment of deduced amino acid sequences of OVGP1 from different mammals including monotreme (Ornithorhynchus anatinus), marsu-
pial (Monodelphis domestica) and placentals (Primates, Glires, Carnivora and Cetartiodactyla). Bars indicate gaps inserted to obtain an optimal align-
ment. A comparison of the amino acid sequences of various mammalian oviductal glycoproteins reveals five distinct regions. The regions A and D are
conserved in the different mammals. The region A corresponding to the amino terminal end has a high degree of identity in monotremes, marsupials
and placentals. The region B shows a low identity among the different mammals and contains multiple insertion/deletion. The region C is an insertion
present only in Mus and the region E is typical of the human, chimpanzee and orangutan. Sequences used to perform the analysis: Homo, U09550;
Chimpanzee, ENSPTRT00000002063; Orangutan, ENSPPYT00000001243; Macaca, U87259; Papio, M59903; Mus, NM_007696; Hamster, D32218;
Rabbit, NM_001082105; Sheep, U17988; Cow, D16639; Pig, U43490; Canis, XM_847145; Monodelphis domestica, XM_001381963; Ornithorhynchus
anatinus, ENSOANT00000024277.
898 Avile
´set al.
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conditions reported that partially purified human OVGP1 becomes
associated with human ZP from an ovarian oocyte isolated from an
antral follicle (O’Day-Bowman et al., 1996). However, the biological
significance of this ZP change in humans remains elusive. Perhaps,
this oviductal maturation of the oocyte could be responsible for the
sperm selection that improves the fertilization and embryo develop-
ment as reported in other species (McCauley et al., 2003). Future
studies using purified human oviductal fluid or recombinant proteins
will provide information about the relevance of this process.
It was previously reported that bovine OVGP1 binds to the porcine
and bovine ZP (Coy et al., 2008), a heterologous interaction that has
been also reported between species not closely related, such as
humans and hamsters. Thus, human OVGP1 bound to the hamster
ovarian ZP in vitro (Reuter et al., 1994). Baboon OVGP1 can bind
human ZP (O’Day-Bowman et al., 1996). Partially purified OVGP1
can bind the ZP of both human and baboon ovarian oocytes (O’Day-
Bowman et al., 1996). The similarities between the different OVGP1
could suggest that a similar role is played by all these proteins;
however, this is not always the case. For example, the incubation of
porcine or bovine oocytes with oviductal secretions decreased the
number of sperm bound to the ZP (Kouba et al., 2000;Coy, et al.,
2008). This result is the opposite of that observed for human and
hamster models (Boatman and Magnoni, 1995;O’Day-Bowman
et al., 1996). Despite the high similarity between human and
baboon OVGP1, baboon OVGP1 produces a significant decrease in
the number of human sperm bound to the human ZP (O’Day-
Bowman et al., 1996). The effects produced in the sperm binding to
the ZP could be produced by the sterical hindrance of the ZP carbo-
hydrates (decrease) or by the exposure of the OVGP1 glycan needed
for the sperm binding (increase).
It has previously been suggested that sperm –oocyte binding is
mediated by a multiple complex involving several sperm plasma mem-
brane proteins and several carbohydrates present in the oocyte extra-
cellular matrix (Thaler and Cardullo, 2002;Rodeheffer and Shur, 2004;
Lyng and Shur, 2007). These carbohydrates are contained specifically
in the ZP proteins and may also be present in the proteins attached to
the ZP once the oocyte enters the oviduct after ovulation (Oikawa
et al., 1988;Rodeheffer and Shur, 2004;Lyng and Shur, 2009). The
different carbohydrates from different glycoprotein origins could be
responsible for the independent sperm binding sites in the ZP and
for the low- and high-affinity sperm binding sites described previously
(Thaler and Cardullo, 1996;Johnston et al., 1998;Mori et al., 2000).
Figure 1 Continued
Oviductal secretions 899
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Zona maturation: ZP hardening and
blockage of polyspermy
Among the functions of the ZP, the prevention of polyspermy during
fertilization is a primary concern (Wassarman et al., 2005;Dean,
2007;Hedrick, 2007;Coy and Avile
´s, 2009); however, this role in
farm animals has been demonstrated to be more complex than
was previously thought. Changes in ZP regulating sperm entry into
the oocyte occur not only after but also before sperm ZP
contact (Coy et al., 2008). We have recently shown that the chemi-
cal and the biological properties of the ZP change when porcine or
bovine oocytes matured in vitro are incubated in oviductal fluid (Coy
et al., 2008). On the one hand, the ZP increases its resistance to
proteolytic digestion from seconds to hours after only 30 min of
contact with oviductal fluid. On the other hand, this modified ZP
decreases its affinity for sperm binding and is less penetrable, result-
ing in reduced levels of polyspermy (Fig. 2). Obviously, passage
through the oviduct adds several molecules to this oocyte coat
and can alter the terminal moieties exposed for the sperm or
enzymes (e.g. proteases). Moreover, according to the view that
spermatozoa penetrate the ZP by physical thrust (Bedford, 2004),
only those with the ability (or the force) to cross the protease resist-
ant (‘hardened’) ZP would successfully fertilize the oocyte. This
finding stresses the importance of the oviductal secretions in the
regulation of polyspermy.
In the above study, it was shown that the molecule responsible for
the observed effects was OVGP1 (Coy et al., 2008). However, inter-
esting specific differences between pig and cow were found. For
example, in pigs, the strongest effect of the oviductal fluid on ZP resist-
ance to proteolysis was observed when the fluid came from adult
animals around ovulation time. In gilts near ovulation, the effect
existed but was 4 times lower. In contrast, oviductal fluid from
either gilts or sows in the luteal phase of the estrous cycle did not
increase ZP resistance to proteolysis, whereas in cattle, almost any
oviductal fluid sample consistently affected ZP resistance to digestion
(authors’ observations). Since it has been shown that OVGP1
secretion is dependent on the estrogen level in plasma in cows and
pigs, among others, new questions arise from these observations:
for example, why does OVGP1 have this effect throughout the
estrous cycle in cows and only during a short temporal window in
Figure 2 Main events produced during the fertilization in the different anatomical regions of the oviduct. A dissected pig oviduct is showed (bar:
1 cm). (A) Ovarian oocytes at the metaphase II stage with expanded cumulus cells are released into the oviductal infundibulum during ovulation. (B)
Once in the oviductal ampulla and exposed to the oviductal fluid, oocytes undergo an oviductal ZP maturation. This maturation includes a pre-
fertilization ZP hardening mediated by OVGP1, at least in the pig and cow species. (C) Later, in the ampullar isthmic junction, the ZP hardening
will decrease the possibilities for sperm–ZP binding and reduce the number of sperm capable of penetrating the oocyte. After fertilization, zona reac-
tion is triggered, avoiding the entry of additional spermatozoa. (D) Isthmus is recognized in many species as the sperm reservoir, and the region where
the last steps of capacitation take place. (E) Isthmus is also the region crossed by the early embryo toward the uterus and the secretion of oviductal
embryotrophic factors contribute to its physiological development.
900 Avile
´set al.
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pigs? Is this a concentration-dependent effect? Or are any other mol-
ecules involved in the role of OVGP1 on ZP modifications?
In mice, ZP resistance to proteases is notacquired in the oviduct (Inoue
and Wolf, 1974;Coy et al., 2008), but, after fertilization, it arises from the
cortical reaction (Barros and Yanagimachi, 1971;Ducibella et al., 1990;
Vincent et al., 1990). Moreover, mouse eggs exposed to bovine oviductal
fluid did not acquire resistance to protease (Coy et al., 2008); however,
very recently, it was demonstrated that a minor fraction of the mice
OVGP1 is able to bind the ZP (Lyng and Shur, 2009). This is another
example, in a general context, of species-specific differences for the
role of the same protein (OVGP1) on the same matrix (ZP).
Returning to the ungulate model, we have demonstrated that, at
least in the case of OVGP1, the presence of heparin in in vitro exper-
iments is necessary to keep the protein bound to the porcine ZP.
Many reports support a role for heparin, a sulfated glycosaminoglycan
(S-GAG), in the capacitation process as well as in the sperm– ZP inter-
action (Bergqvist and Rodrı
´guez-Martı
´nez, 2006). Our recent results
introduce a new role for oviductal S-GAGs. Porcine and bovine ZPs
from in vitro matured oocytes incubated in a medium with heparin
and without oviductal fluid did not acquire pronase resistance
(authors’ observations). Similarly, the presence of heparin in the
IVF medium did not reduce sperm–ZP binding. However, heparin
acts as a modulator of the ZP modifications described in oviductal
secretions. So, the ZP network that contains OVGP1 and other
elements surrounding oocytes in the oviduct is stabilized by the
binding of S-GAGs, modifying ZP solubility and consequently making
it more resistant to sperm penetration. The mean content of total
S-GAGs in tubal fluid differs among species and could partially
explain the different effects observed in different species (Tienthai
et al., 2000;Bergqvist and Rodrı
´guez-Martı
´nez, 2006).
In light of this contribution of oviductal secretions to the biological
activity of the ZP, we consider that the concept of zona maturation
(classically used to describe the changes in the ZP during the folliculo-
genesis) should be reconsidered to include two different aspects: (i)
ovarian maturation and (ii) oviductal maturation (Fig. 2).
How does OVGP1 play a different role
in different species?
This question remains unresolved but there are different hypotheses
that will need to be tested in the future. First, the different biological
activities could be due to the different protein sequence (Fig. 1).
Additionally, it was suggested that positive Darwinian selection pro-
motes the divergence of the OVGP1 in different mammals
(Swanson et al., 2001). Second, the different biological roles played
by the OVGP1 could be due to the different grade of glycosylation
and/or to different splicing and polymerization forms. Carbohydrates
mainly present in O-linked chains are a major OVGP1 component
(Malette and Bleau, 1993). Glycosylation differences detected in the
estrous cycle could be responsible for a different biological role of
the oviductal-secreted glycoproteins (McBride et al., 2004,2005).
Thus, only a minor fraction of the mouse OVGP1, recognized by
the PNA lectin, is able to bind the ZP (Lyng and Shur, 2009). Recently,
we reported that only two bovine OVGP1s of 75 and 95 kDa have
the ability to bind to porcine ZP and are responsible for the hardening
observed when the ZPs are incubated in oviductal fluid and for
increased monospermy (Coy et al., 2008). The exact role played by
the different glycoforms in the different species should therefore be
addressed. Third, the OVGP1 activity could be affected by ZP compo-
sition. The protein composition of the ZP has to be taken into con-
sideration because different mammals have different compositions.
In mammals, ZP is formed by three or four proteins (Bleil and
Wassarman, 1980;Lefievre et al., 2004;Boja et al., 2005;Hoodbhoy
et al., 2005;Goudet et al., 2008;Izquierdo-Rico et al., 2009).
Additionally, in the three proteins’ model, it was observed that ZP1
is present in mice; however, in porcine and bovine ZP, ZP4 is
present but not ZP1 (Goudet et al., 2008). The relevance of the differ-
ent composition of ZP to the OVGP1 interaction should be investi-
gated in the future. In this context, the use of oviductal fluids and
oocytes from different species and different recombinant OVGP1 pro-
teins could provide valuable new information about the role played by
the OVGP1 in fertilization, hardening of the ZP and binding to the ZP.
Oviductal secretions and embryo
development
The first week of development represents the interval called
preimplantation or pre-attachment development (depending on the
species), which is a uniquely mammalian phenomenon and encom-
passes the free-living period of mammalian development during
which the early conceptus traverses the oviduct and gains access to
the uterine environment. Blastocysts form with two cell types: the tro-
phectoderm, which develops into the embryonic portion of the pla-
centa, and the inner cell mass, which develops into the embryo
proper. The embryo in its early stage of development does not
need contact with the maternal tract to regulate its own cell division
and differentiation. Preimplantational embryos can develop in vitro
and can produce normal offspring after embryo transfer; however,
the development of preimplantation mammalian embryos in vitro is
compromised compared with those grown in vivo. In humans, it was
observed that the in vitro development of embryos to the blastocyst
stage is not an efficient process, ranging from 15% to 26% of
success (Fehilly et al., 1985;Bongso et al., 1989;Dokras et al.,
1991). Thus, in a previous study after the analysis of more than 550
bipronucleate embryos, it was reported that only 26% of the
embryos reached the blastocyst stage (Dokras et al., 1993). Other
studies performed later have observed an increase in the percentage
of blastocyst that can be higher than 50% depending on the culture
condition, the age of the oocytes and other parameters (see review
Gardner et al., 1998;Dumoulin et al., 1999;Pantos et al., 1999;
Schoolcraft et al., 1999;Smith, 2002;Van Landuyt et al., 2005).
Deprivation of some in vivo-produced maternal factors could be
responsible for impaired in vitro development and viability (Rizos
et al., 2002) and for some pathological alterations associated with in
vitro-produced embryos (Fernandez-Gonzalez et al., 2007,2008).
However, it is important to take into consideration that other
factors such as chromosome defects contribute to the low efficiency
of blastocyst formation in addition to the suboptimal culture condition
(Gekas et al., 2001).
The female reproductive tract modifies its activity in order to provide
the optimal environment for the development of the embryo (Buhi,
2002). It has been reported that cannabinoid signaling may coordinate
smooth muscle contraction and relaxation for embryo transport in
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the oviduct (Wang et al., 2004). In addition to embryo transport, the
oviduct produces a number of factors, and many of their corresponding
receptors are present in embryos (Kane et al., 1997;Lee and Yeung,
2006). Several studies have identified embryotrophic factors from the
oviduct and have analyzed the effects of such factors on the morpho-
logical development of embryos during preimplantation (Kane et al.,
1997;McCauley et al., 2003;Lee et al., 2006). Some of the oviductal
proteins and factors that display embryotrophic activity in vitro are
described in Supplementary Table S1 and reviewed by Lee and Yeung
(2006). In addition, oviductal embryotrophic factors can act during
different stages of development. We have recently shown that cleavage
and blastocyst development rates in pigs were significantly higher from
oviductal fluid-treated oocytes than from untreated oocytes. The ovi-
ductal fluid protects the embryo against adverse impacts on mtDNA
transcription/replication and apoptosis (Lloyd et al., 2009). However,
scarce information exists about the physiological role played by the
majority of the proteins present in the oviductal fluid (Supplementary
Table S1) and their contributions to the fertilization and embryonic
development, especially in humans. Animal models could play an impor-
tant role in clarifying their roles.
During the secretory phase of the estrus cycle, the oviductal epi-
thelium releases various biomolecules to the lumen to enhance
embryo development. This secretory activity of the oviduct is regu-
lated by steroid hormones and also modulated by gametes and
embryos. Interaction between preimplantation embryos and the
maternal genital tract has been suggested. The preimplantation
embryo may reveal its presence even before arrival in the uterus
because there is evidence that it can affect both the expression of ovi-
ductal genes and its own transport (Lee et al., 2006). It has been
reported that some receptors of embryonic factors affecting oviductal
physiology, like the receptor for the embryo-derived platelet-activating
factor, are present in the oviducts of humans and cows (Tiemann
et al., 2001;Velasquez et al., 2001). Oviducts maintain the production
of demilune cell parotid protein in the presence of preimplantation
mouse embryos, improving subsequent embryo development (Lee
et al., 2009). Also, the human oviduct-derived embryotrophic
factor-3 contains complement protein-3 (C3), which is not embryo-
trophic, but is converted into the embryotrophic derivate iC3b. It
has been reported that the presence of embryo and steroid hormones
regulates the synthesis and secretion of oviductal C3, phospholipid
transfer protein and amphiregulin (Lee et al., 2005,2006,2009).
Some embryotrophic factors present in the oviduct may not be
species-specific. The oviductal environment supports embryonic
growth up to the blastocyst stage across a wide range of species fol-
lowing trans-species transfer (Rizos et al., 2007). The use of such inter-
mediate hosts for the culture of zygotes fertilized in vitro or in vivo is
not a recent phenomenon but while in the early days it was a necess-
ary means of achieving development before the development of ade-
quate in vitro culture systems (Gandolfi and Moor, 1987), nowadays
such systems are used to produce embryos of superior quality
(Gutierrez-Adan et al., 2004). For example, the culture of bovine fer-
tilized oocytes in the ewe oviduct does not produce more blastocysts
than following culture in vitro; however the quality of the blastocysts is
improved significantly (Rizos et al., 2002).
Early-cleavage embryos are able to cope with environmental stress
and can grow in a wide range of culture conditions, indicating that pre-
implantation embryos can readily adapt to their culture environment.
This adaptive response to the environment operates through the
alternative activation or deactivation of developmental gene
expression and phenotypes (Fernandez-Gonzalez et al., 2007). Con-
trary to the view that early embryos are the most fragile stages of
life, mammalian preimplantation embryos exhibit remarkable plasticity
and will attempt to form blastocysts under a wide range of culture
conditions, although, presumably, at some adaptive cost to their
post-gestational development program. Such plasticity may turn out
to be unsuitable and lead to adult disease (Ecker et al., 2004;
Fernandez-Gonzalez et al., 2004). The only optimal microenvironment
for embryo development is the oviduct. Understanding the oviductal
environment and the factors secreted by the oviduct is important
for reproducing the in vivo condition in vitro and eliminating any long-
term effects produced by the in vitro conditions.
In humans, it was reported that a better implantation rate (as high
as 50%) was obtained by using the blastocyst transfers following in vivo
fertilization, uterine flushing and embryo donation (Croxatto et al.,
1972;Buster et al., 1985). Moreover, a recent study suggests that
better results are obtained when blastocysts are transferred to the
female uterus compared with the transfer of cleavage-stage embryos
(Papanikolaou et al., 2008) probably due to a better synchronization
between the embryo and the uterus. The chief advantage of producing
a superior embryo lies in the decreased risk of multiple pregnancies.
With this in mind, the studies to date suggest that further research
will result in the development of an optimal embryo culture medium
in the near future.
Concluding remarks
A universal characteristic of the mammalian oocyte is the passage of
the cell through the Fallopian tube (oviduct). Much evidence indicates
that this complex conduit plays a key role in fertilization and early
embryo development in vivo. Despite the great advances in assisted
reproductive techniques, it seems that the oviduct is necessary for
optimal gamete maturation, capacitation, selection and embryo devel-
opment. Thus, the relevance of the oviducts’ contribution seems to
differ between animal models; however, key processes are usually
conserved in different species. Detailed information about the
oviduct secretion and function is lacking, especially in humans due to
the difficulty in obtaining appropriate samples. We are convinced
that in the near future the detailed knowledge of the oviductal tran-
scriptome and secretome to be achieved through robust technology
and the use of appropriate animal models will throw further light on
the role played by the oviduct. The use of animal models will
provide us detailed information about the different components
present in the oviduct, and their effects on the gamete biology, ferti-
lization and embryo development. These experimental approaches
will allow us to develop better embryo culture medium and condition
to improve the low rate of blastocyst formation and also their quality
in humans.
Supplementary material
Supplementary material is available at http://molehr.oxfordjournals.
org/.
902 Avile
´set al.
by guest on November 22, 2010molehr.oxfordjournals.orgDownloaded from
Acknowledgements
We thank all the members of our laboratories for their scientific con-
tributions which have led to the proposal of the different ideas
expressed in this review. We thank Dr Pascale Chevret (Laboratoire
de Biome
´trie et Biologie E
´volutive, a
`l’Universite
´de Lyon 1, France) for
preparing Fig. 1.
Funding
Research carried out in the authors’ laboratory was supported
by the Spanish Ministry of Science and Innovation and FEDER
(AGL2009-12512-C02-01-02; AGL2009-11358) and Fundacio
´n
Seneca of the Comunidad Auto
´noma de la Regio
´n de Murcia
(0452/GERM/06, 11996/PI/09).
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... Oviductal environment is composed of oviductal fluid and the oviductal epithelium which is consist of cilia and secretory cells (10,12,13). While secretory cells contribute to the formation of the oviductal fluid, the cilia allows the oocytes to be transported in the oviductal fluid with the help of their hit and to form the sperm reserves in the isthmus region interacting with the spermatozoa (10,14,15,16). The content of the oviduct fluid is shaped by the secretions of oviduct secretory epithelial cells as well as blood plasma, small contributions from follicular and peritoneal fluid (10,16). ...
... While secretory cells contribute to the formation of the oviductal fluid, the cilia allows the oocytes to be transported in the oviductal fluid with the help of their hit and to form the sperm reserves in the isthmus region interacting with the spermatozoa (10,14,15,16). The content of the oviduct fluid is shaped by the secretions of oviduct secretory epithelial cells as well as blood plasma, small contributions from follicular and peritoneal fluid (10,16). Oviductal fluid consists of many different components, including different proteins, growth factors, hormones, enzymes, receptors, defense agents etc. (16). ...
... The content of the oviduct fluid is shaped by the secretions of oviduct secretory epithelial cells as well as blood plasma, small contributions from follicular and peritoneal fluid (10,16). Oviductal fluid consists of many different components, including different proteins, growth factors, hormones, enzymes, receptors, defense agents etc. (16). The protein and lipid concentrations (17,18), enzymatic activities (19,20), as well as gene expression of oviduct epithelial cells (21) change dynamically at different stages of estrus cycle. ...
... These miRNAs could possibly originate from follicular fluid (FF). FF is predicted to flux into the oviduct during ovulation because hormones found at high concentrations in FF were also detected in OF in golden hamsters [17], and hormone and protein concentrations in the ipsilateral oviduct of ovulated ovaries differ from those of their contralateral counterparts [18]. ...
... The contribution of FF to the embryonic environment has been indicated by the evidence that OF profiles [18] and gene expression in oviductal epithelial cells [10] and hormone concentration in OF [17] differ between ipsilateral and contralateral ovulation sides. Asaadi et al. [26] showed that the size and concentration of EVs are similar in OF and FF in cows; the supplementation of oocyte maturation medium with EVs of FF or OF improved embryonic development. ...
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Global methylation levels differ in in vitro- and in vivo-developed embryos. Follicular fluid (FF) contains extracellular vesicles (EVs) containing miRNAs that affect embryonic development. Here, we examined our hypothesis that components in FF affect global DNA methylation and embryonic development. Oocytes and FF were collected from bovine ovaries. Treatment of zygotes with a low concentration of FF induced global DNA demethylation, improved embryonic development, and reduced DNMT1/3A levels. We show that embryos take up EVs containing labeled miRNA secreted from granulosa cells and the treatment of zygotes with EVs derived from FF reduces global DNA methylation in embryos. Furthermore, the methylation levels of in vitro-developed blastocysts were higher than those of in their vivo counterparts. Based on small RNA-sequencing and in silico analysis, we predicted miR-29b, -199a-3p, and -148a to target DNMTs and to induce DNA demethylation, thereby improving embryonic development. Moreover, among FF from 30 cows, FF with a high content of these miRNAs demethylated more DNA in the embryos than FF with a lower miRNA content. Thus, miRNAs in FF play a role in early embryonic development.
... Moreover, dysregulation of these may be directly involved in the occurrence of TEP-like conditions affecting fertility [7,32] . The oviduct secretions have been well characterized and new components are also being identified which include growth factors, cytokines, various hormones, and their receptors, various enzymes; some of these are exclusive to the FT [33] . Since existing evidence indicates the roles of gonadotrophins in modulating the oviductal functions synergistically with steroids and other bioactive molecules highlighting the tight and fine interactions between the FT and the embryo, further applied research is warranted to use the available information to improve the in vitro embryo manipulation and in vitro fertilization and embryo transfer (IVF-ET). ...
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Human fallopian tubes (FTs) play important roles in the whole reproductive process. FTs are the site for the final maturation of gametes, fertilization, transport of preimplantation embryos, and early embryonic development before entering the uterus. All these functions are critical in the establishment of a successful pregnancy. When the embryo is in transit through the FT, the FT microenvironment changes through endocrine, paracrine, autocrine, and juxtacrine mechanisms which involve various hormones and bioactive substances mainly from the neighboring cells. Therefore, the interactions between the embryo and the FT may be the earliest embryo-maternal communications that are essential for the establishment of pregnancy. This review critically discusses the evidence of various hormonal and bioactive mediated control of the microenvironment in the FTs during the earliest embryo-maternal communications. Moreover, we highlight existing gaps in the knowledge and the importance of exploring more of the physiology of FTs which will hold the key to producing high-quality embryos for patients seeking in vitro fertilization (IVF) treatments.
... Un modo de lograr este objetivo sería mediante la adición de fluidos reproductivos de fases específicas del ciclo estral en los medios de cultivo. Los fluidos folicular, oviductal y uterino contienen diversos elementos reguladores específicos, como hormonas, factores de crecimiento y citoquinas (Block et al., 2011;Cajas et al., 2021), carbohidratos, iones, lípidos, fosfolípidos y proteínas (Avilés et al., 2010), que, al ser agregados a los medios de cultivo, son capaces de mejorar el desarrollo de los embriones preimplantatorios obtenidos por FIV (Hamdi et al., 2018). ...
... OVGP1 (oviduct-specific glycoprotein 1) is an estrogendependent protein that is found in the oviductal fluid of different mammalian species, including bovine. OVGP1 (oviduct-specific glycoprotein 1) plays an important role in the processes of fertilization, sperm capacitation, and embryonic development [69,70]. During fertilization, OVGP1 binds to the zona pellucida of oocytes and modifies the matrix structure to allow sperm penetration [71]. ...
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Infertility is a major problem in farm animals, which has a negative economic effect on farm industries. Infertility can be defined as the inability of animals to achieve a successful pregnancy. Early pregnancy is crucial to establish a successful pregnancy, and it is reported that 70-80% and 20-30% of total embryonic loss occur in cattle and pigs, respectively, during the first month of pregnancy. The advanced high-throughput proteomics techniques provide valuable tools for in-depth understanding of the implantation process in farm animals. In the present review, our goal was to compile, assess, and integrate the latest proteomic research on farm animals, specifically focused on female reproduction, which involves endometrial tissues, uterine fluids, oviductal fluids, and mi-croRNAs. The series of studies has provided in-depth insights into the events of the implantation process by unfolding the molecular landscape of the uterine tract. The discussed data are related to pregnant vs. non-pregnant animals, pregnancy vs. oestrous cycle, different days of the early pregnancy phase, and animals with uterine infections affecting reproduction health. Some of the studies have utilized non-invasive methods and in vitro models to decipher the molecular events of embryo maternal interaction. The proteomics data are valuable sources for discovering biomarkers for infertility in ruminants and new regulatory pathways governing embryo-uterine interaction, endo-metrium receptivity, and embryonic development. Here, we envisage that the identified protein signatures can serve as potential therapeutic targets and biomarkers to develop new therapeutics against pregnancy diseases.
... Until the implantation, the embryo is nourished by substances produced by oviductal and uterine epithelial cells (63). These oviductal and uterine fl uids include proteins, lipids, phospholipids, and other nutrients (64,65). Moreover, the oviduct contains the glycoprotein oviductin, which plays role in the embryo development, sperm capacitation, and oocyte binding with sperm cells (66). ...
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A 120-kDa oviduct-specific glycoprotein is synthesized and secreted into the oviductal lumen during estrogen dominance in the human. The objective of this investigation was to clone, sequence, and characterize the cDNA to this core protein. Rapid amplification of cDNA ends was used to clone a contiguous 3' CDNA end and 5' cDNA end. The total length of the cDNA was determined to be 2.2 kb by sequence analysis and exhibited a 92% sequence identity with the comparable overlapping baboon cDNA (1.2 kb). A high degree of homology was found to the N-terminal sequence of hamster oviductin and the partial sequence of a homologous baboon and bovine oviduct glycoprotein. Northern blots revealed a single mRNA species of 2.4 kb. Using RNA from various tissues of an estrogen-treated baboon, we found that the mRNA for the oviductal glycoprotein was present only in the oviduct. Hybridization was detected to an mRNA of similar size from oviductal tissue of the baboon, hamster, and mouse and to an mRNA of slightly smaller size in the rabbit, cow, and cat but not to any mRNA species from rat oviductal RNA. Slot-blot analysis showed that the message was present in significantly greater (p < 0.05) concentrations in RNA from oviductal tissue from the late follicular stage than from the early follicular, early or late luteal, or postpartum stages. In conclusion, we have isolated the complete cDNA for a human oviductal glycoprotein. The presence of significantly greater amounts of the mRNA during the late follicular phase of the menstrual cycle is consistent with the proposed estrogen control. The mRNA for the oviductal glycoprotein is present only in the oviduct of an estrogen-treated baboon, and a cross-hybridizing RNA is found in oviductal RNA from various mammals.
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During late follicular growth, oestrus, fertilization and early embryonic development, the oviduct, under specific hormonal control, produces fluid and contributes secretory macromolecules that optimize the microenvironment for gamete maturation and transport, fertilization and early cleavage-stage embryonic development. This review describes the state of knowledge concerning the physiological and biochemical characterization of the major oviduct secreted protein, the oviduct-specific, oestrogen-dependent glycoprotein. The identification, localization within the oviduct, binding and association with oocytes, embryos and spermatozoa, hormonal control of gene expression, cloning, gene organization, protein sequences and post-translational modifications of oviduct-specific, oestrogen-dependent glycoprotein are discussed. Identification of biological functions for this glycoprotein, its interactions with spermatozoa, oocytes and embryos and its potential as a paracrine regulator of fertilization and development are also discussed.
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A specific 85-97-kDa (95-kDa) glycoprotein was found in bovine oviductal tissue and fluid during the follicular phase. In this study, a 95-kDa bovine oviductal glycoprotein (95-kDa BOGP) was purified by wheat germ agglutinin affinity and Mono-Q ion-exchange column chromatography. The first 29 NH2-terminal amino acid residues were determined by gas-phase microsequencing. A cDNA expression library prepared from poly(A)+ RNA isolated from bovine oviducts was screened with a monoclonal antibody to 95-kDa BOGP. A single positive clone containing a approximately 2-kb cDNA insert was isolated. The coding region contained 1612 bp translating to 537 amino acids. The derived amino acid sequence contained a partial signal sequence of 18 amino acids followed by 29 amino acids that were identical to the NH2-terminal amino acids determined by protein sequencing of purified 95-kDa BOGP. The amino acid sequence predicted a mature protein of 519 amino acids (57,684 daltons) containing one potential N-linked glycosylation site and five cysteines. Northern blot hybridization with a digoxigenin-labeled probe indicated that a single message of approximately 2.5 kb was present in oviductal RNA, and this message was detected in significantly greater amounts in oviductal RNA during the follicular phase than during the luteal phase. The amino acid sequence of a portion of 95-kDa BOGP was highly homologous (71% identity) to that of a baboon oviduct-specific glycoprotein.
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Our objective in this study was to complete the sequence of the baboon oviductal glycoprotein, examine the hormonal regulation of the oviductal glycoprotein mRNA, and determine whether there was a regional variation within the oviduct in the level of oviductal glycoprotein mRNA expression. Finally, because of the structural similarity of the amino terminal end of the oviductal glycoprotein to chitinases, we sought to determine whether the oviductal glycoprotein functions as a glycosyl hydrolase. The total transcript length of the baboon oviductal glycoprotein was determined to be 2228 nucleotides in length plus a poly(A) tail. The largest open reading frame was 623 amino acids, which would produce a protein of 69.3 kDa. The first 420 amino acids were highly homologous to the amino acid sequence of other oviductal glycoproteins, but the remainder of the sequence differed considerably from that of all other species except the human. Although the N-terminal region exhibited sequence similarity to chitinases, the oviductal glycoprotein did not exhibit any activity towards typical chitinase substrates. The oviductal glycoprotein mRNA levels were elevated to approximately the same extent in the fimbria, ampulla, and isthmus of the oviduct after estradiol treatment and in the late follicular stage of the menstrual cycle. The oviductal glycoprotein mRNA levels were lower in the early follicular stage and early luteal stage and were not detectable in the late luteal stage or in progesterone-treated baboons. These results indicate that the oviductal glycoprotein mRNA is induced by estradiol and is present at the highest levels at the time of fertilization. Although there is structural homology with chitinases, no such glycosyl hydrolase activity could be detected. However, the common structure of the N-terminal region of the oviductal glycoproteins implies that it has the same, as yet unknown, function in all species.
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There is growing evidence that the oviduct is not a passive conduit for gamete and embryo transport but serves a function for the gametes and/or embryos. The oviductal epithelium secretes one or more specific glycoproteins that associate with the egg after ovulation. Several published reports including our preliminary studies have suggested that the egg-associating glycoprotein(s) from the oviduct exists in several mammalian species including golden hamster. However, little or almost no biochemical characterization of the hamster oviduct-specific glycoprotein (HOGP) has been reported. To analyze the molecular structure of the HOGP in detail, we have attempted molecular cloning of cDNA corresponding to HOGP. A cDNA library constructed from the hamster oviduct in the phage vector lambda ZAPII was screened with digoxigenin-labeled, baboon oviduct-specific glycoprotein cDNA as the probe. A single positive clone was isolated, and the nucleotide sequence of the isolated cDNA was determined. Rapid amplification of cDNA end was carried out to obtain a proximal 5' cDNA end of the clone. The cDNA clone consisted of 2387 bp, and the coding region contained 2013 bp translating to 671 amino acids. The amino acid sequence deduced from the cDNA sequence confirmed the chemically determined NH2-terminal sequence of a HOGP and suggested that the derived amino acid sequence contained a signal peptide region (21 amino acids) and 650 amino acids (70,890 daltons) of the mature form of the HOGP region. The amino acid sequence of HOGP appeared to have eight potential N-glycosylation sites. Northern blot analysis revealed that a single message of approximately 2.5 kb was present in oviductal RNA but not in the RNA of several other hamster tissues. The HOGP showed high amino acid sequence homology with baboon, bovine, and human oviduct-specific glycoprotein. These results demonstrate that an oviduct-specific glycoprotein homologue gene exists in various mammalian species including rodent.