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Nell-1 induces acrania-like cranioskeletal deformities during mouse embryonic development
Abstract and Figures
We previously reported NELL-1 as a novel molecule overexpressed during premature cranial suture closure in patients with craniosynostosis (CS). Nell-1 overexpression also results in premature suture closure/craniosynostosis in newborn transgenic mice. On a cellular level, increased levels of Nell-1 induce osteoblast differentiation and apoptosis. In this report, mice over-expressing Nell-1 were examined during embryonic development as well as shortly after birth for further analysis of craniofacial defects including neural tube defects (NTDs). The results demonstrated that overexpression of Nell-1 could induce acrania at relatively late gestation stage (E15.5) in mouse embryos, through massive apoptosis in calvarial osteoblasts and neural cells. The induced apoptosis was associated with an increase in Fas and Fas-L production. In addition, transgenic E15.5 and newborn transgenic mice with the CS phenotype displayed distortion of the chondrocranium associated with premature hypertrophy and increased apoptosis of chondrocytes. These findings were also verified in vitro with primary chondrocytes transduced with AdNell-1. In conclusion, Nell-1 overexpression can induce craniofacial anomalies associated with neural tube defects during embryonic development and may involve mechanisms of massive apoptosis associated with the Fas/Fas-L signaling pathway. NELL-1: used when describing the human gene; NELL-1: used when describing the human protein; Nell-1: used when describing the rodent gene; Nell-1: used when describing the rodent protein.
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... (39) In addition, we also reported integrin-b1 binding to the C-terminus of Nell-1. (41,42) Integrin-b1, however, is not Nell-1-specific because integrin-b1 binds promiscuously with a broad range of molecules. (41,43,44) During the search for a specific cell surface receptor for Nell-1-mediated osteogenesis, we unexpectedly identified a high-binding affinity, ligand/receptor-like interaction between Nell-1 and Cntnap4. ...
... (41,42) Integrin-b1, however, is not Nell-1-specific because integrin-b1 binds promiscuously with a broad range of molecules. (41,43,44) During the search for a specific cell surface receptor for Nell-1-mediated osteogenesis, we unexpectedly identified a high-binding affinity, ligand/receptor-like interaction between Nell-1 and Cntnap4. Transmembrane receptor Cntnap4 has known roles in connecting pre-and post-synapses critical to synapse development and cortical interneuron function. ...
... unexpected discovery of Cntnap4 as a cell membrane binding protein for Nell-1 in osteogenic-committed cells, and Nell-1 as a ligand of Cntnap4, provides a foundational framework for the broader investigation of the Nell-1/Cntnap4 functional axis. From an osseous standpoint, Nell-1-overexpressing mice exhibit a spectrum of anomalies ranging from craniosynostosis to acrania, (41) whereas N-ethyl-N-nitrosourea (ENU)-induced Nell-1-deficient mice exhibit calvarial defects similar to human cleidocranial dysplasia (CCD) patients. (11) In this study, when we focused on calvarial skeletal development, Cntnap4 deficiency on osteogenesis was evidenced at the onset of Wnt1-Cre expression (Fig. 7). ...
... Nell1 is a large secretory glycoprotein, and was originally identified in craniosynostosis patients as being specifically upregulated within prematurely fusing sutures [53]. Nell1 deficiency severely disrupts bone growth, as mice with nonsense mutations in Nell1 die perinatally with major skeletal anomalies in the craniofacial complex, spine, and long bones [54,55]. Conversely, transgenic Nell1-overexpressing mice recapitulate craniosynostosis-like phenotypes [56]. ...
... Conversely, transgenic Nell1-overexpressing mice recapitulate craniosynostosis-like phenotypes [56]. Accordingly, several recent studies indicate that Nell1 exerts osteoinductive activity [55,57]. ...
Background:
BMP9 induces both osteogenic and adipogenic differentiation of mesenchymal stem cells (MSCs). Nell1 is a secretory glycoprotein with osteoinductive and anti-adipogenic activities. We investigated the role of Nell1 in BMP9-induced osteogenesis and adipogenesis in MSCs.
Methods:
Previously characterized MSCs iMEFs were used. Overexpression of BMP9 and NELL1 or silencing of mouse Nell1 was mediated by adenoviral vectors. Early and late osteogenic and adipogenic markers were assessed by staining techniques and qPCR analysis. In vivo activity was assessed in an ectopic bone formation model of athymic mice.
Results:
We demonstrate that Nell1 expression was up-regulated by BMP9. Exogenous Nell1 potentiated BMP9-induced late stage osteogenic differentiation while inhibiting the early osteogenic marker. Forced Nell1 expression enhanced BMP9-induced osteogenic regulators/markers and inhibited BMP9-upregulated expression of adipogenic regulators/markers in MSCs. In vivo ectopic bone formation assay showed that exogenous Nell1 expression enhanced mineralization and maturity of BMP9-induced bone formation, while inhibiting BMP9-induced adipogenesis. Conversely, silencing Nell1 expression in BMP9-stimulated MSCs led to forming immature chondroid-like matrix.
Conclusion:
Our findings indicate that Nell1 can be up-regulated by BMP9, which in turn accelerates and augments BMP9-induced osteogenesis. Exogenous Nell1 may be exploited to enhance BMP9-induced bone formation while overcoming BMP9-induced adipogenesis in regenerative medicine.
... Indeed, Nell-1 is expressed in neuroblastoma cell lines, glioblastoma cell lines, and adult brain and even at a much higher level in the embryonic inferior olive and spinal cord (Li, Zheng, Ha, et al. 2018). However, the function of Nell-1 in the neural system has not yet been well investigated, although extreme Nell-1 overexpression may cause massive apoptosis of neural cells in the developing brain (Zhang et al. 2006). The recently distinguished association between the single-nucleotide polymorphisms of Nell-1 and autism (Li, Zheng, Ha, et al. 2018), bipolar disorder (Mathieu et al. 2015), and depression ) further emphasizes the potential importance of Nell-1 in the nervous system. ...
Neural EGFL-like 1 (Nell-1) is a well-studied osteogenic factor that has comparable osteogenic potency with the Food and Drug Administration–approved bone morphogenic protein 2 (BMP-2). In this review, which aims to summarize the advanced Nell-1 research in the past 10 y, we start with the correlation of structural and functional relevance of the Nell-1 protein with the identification of a specific receptor of Nell-1, contactin-associated protein-like 4 (Cntnap4), for osteogenesis. The indispensable role of Nell-1 in normal craniofacial and appendicular skeletal development and growth was also defined by using the newly developed tissue-specific Nell-1 knockout mouse lines in addition to the existing transgenic mouse models. With the achievements on Nell-1’s osteogenic therapeutic evaluations from multiple preclinical animal models for local and systemic bone regeneration, the synergistic effect of Nell-1 with BMP-2 on osteogenesis, as well as the advantages of Nell-1 as an osteogenic protein with antiadipogenic, anti-inflammatory, and provascularized characteristics over BMP-2 in bone tissue engineering, is highlighted, which lays the groundwork for the clinical trial approval of Nell-1. At the molecular level, besides the mitogen-activated protein kinase (MAPK) signaling pathway, we emphasize the significant involvement of the Wnt/β-catenin pathway as well as the key regulatory molecules Runt-related transcription factor 2 (Runx2) in Nell-1-induced osteogenesis. In addition, the involvement of Nell-1 in chondrogenesis and its relevant pathologies have been revealed with the participation of the nuclear factor of activated T cells 1 (Nfatc1), Runx3, and Indian hedgehog (Ihh) signaling pathways, although the mechanistic insights of Nell-1’s osteochondrogenic property will be continuously evolving. With this perspective, we elucidate some emerging and novel functional properties of Nell-1 in oral-dental and neural tissues that will be the frontiers of future Nell-1 studies beyond the context of bone and cartilage. As such, the therapeutic potential of Nell-1 continues to evolve and grow with continuous pursuit.
... It is significant that Nell-1 becomes a newly identified factor in contributing to the pathogenesis of postnatal hydrocephalus. The dual role of Nell-1 in osteochondral and neural tissue development and growth as evidenced in this study may provide a new research avenue to the growing field of neuroskeletal biology [3,54,[67][68][69][70]. Fig. 6 Nell-1 inactivation significantly alters Wnt/β-catenin signaling in CNCCs and cranial bone derivatives of newborn mice. ...
Upregulation of Nell-1 has been associated with craniosynostosis (CS) in humans, and validated in a mouse transgenic Nell-1 overexpression model. Global Nell-1 inactivation in mice by N-ethyl-N-nitrosourea (ENU) mutagenesis results in neonatal lethality with skeletal abnormalities including cleidocranial dysplasia (CCD)-like calvarial bone defects. This study further defines the role of Nell-1 in craniofacial skeletogenesis by investigating specific inactivation of Nell-1 in Wnt1 expressing cell lineages due to the importance of cranial neural crest cells (CNCCs) in craniofacial tissue development. Nell-1flox/flox; Wnt1-Cre (Nell-1Wnt1 KO) mice were generated for comprehensive analysis, while the relevant reporter mice were created for CNCC lineage tracing. Nell-1Wnt1 KO mice were born alive, but revealed significant frontonasal and mandibular bone defects with complete penetrance. Immunostaining demonstrated that the affected craniofacial bones exhibited decreased osteogenic and Wnt/β-catenin markers (Osteocalcin and active-β-catenin). Nell-1-deficient CNCCs demonstrated a significant reduction in cell proliferation and osteogenic differentiation. Active-β-catenin levels were significantly low in Nell-1-deficient CNCCs, but were rescued along with osteogenic capacity to a level close to that of wild-type (WT) cells via exogenous Nell-1 protein. Surprisingly, 5.4% of young adult Nell-1Wnt1 KO mice developed hydrocephalus with premature ossification of the intrasphenoidal synchondrosis and widened frontal, sagittal, and coronal sutures. Furthermore, the epithelial cells of the choroid plexus and ependymal cells exhibited degenerative changes with misplaced expression of their respective markers, transthyretin and vimentin, as well as dysregulated Pit-2 expression in hydrocephalic Nell-1Wnt1 KO mice. Nell-1Wnt1 KO embryos at E9.5, 14.5, 17.5, and newborn mice did not exhibit hydrocephalic phenotypes grossly and/or histologically. Collectively, Nell-1 is a pivotal modulator of CNCCs that is essential for normal development and growth of the cranial vault and base, and mandibles partially via activating the Wnt/β-catenin pathway. Nell-1 may also be critically involved in regulating cerebrospinal fluid homeostasis and in the pathogenesis of postnatal hydrocephalus.
... Nell-1 is osteochondral specific for inducing premature suture closure in human craniosynostosis and chondrogenic or osteoblastic differentiation [7,8,[31][32][33]. When adenovirus-mediated (Ad-) Nell-1 and Ad-BMP2 were transferred to bone marrow stromal cells (BMSCs) from adult goats or injected into the intermuscular spaces of nude mice, Nell-1 had a promotive effect on the osteogenic differentiation of BMSCs similar to that of bone morphogenetic protein-2 (BMP2) [34]. ...
Background/aims:
This study aimed to investigate the effect of Nell-1 on the osteogenic behaviors of pre-osteoblasts on titanium (Ti) surfaces and to identify the underlying signaling pathway.
Methods:
Nell-1 at different concentrations was added to culture medium to stimulate MC3T3-E1 subclone 14 on Ti surfaces. A CCK-8 colorimetric assay was used to detect cell proliferation. Alkaline phosphatase activity (ALP) assay and enzyme-linked immunosorbent assay (ELISA) were used to evaluate ALP activity and the osteocalcin (OCN) secretion, respectively. Indicators of osteoblastic differentiation were assessed using real-time polymerase chain reaction analysis (RT-PCR). Western blot (WB) assay was used to analyze the expression changes of the osteogenic proteins and the mitogen-activated protein kinase (MAPK) pathway.
Results:
Nell-1 significantly increased the osteogenic gene and protein expression levels of ALP, OCN, Runx2, osteoprotegerin (OPG), collagen type I (Col-I), and Osterix (Osx) in pre-osteoblasts on Ti surfaces. The optimal concentration of Nell-1 was 100 ng/ ml. In addition, Nell-1 activated ERK and JNK, but not P38, in MC3T3-E1 cells on the Ti surface. Except for ALP and Col-I, the promotive effects of Nell-1 on the expression of osteogenic markers were suppressed by ERK inhibitor U0126.
Conclusion:
Certain concentrations of Nell-1 can promote the osteogenic differentiation of pre-osteoblasts on Ti surfaces by activating the MAPK/ERK signaling pathway.
... Historically, previous research has focused on revealing the role of Nell-1 in the development of craniofacial skeletons. (1,2,8,(12)(13)(14)(15) In contrast to intramembranous bone formation in craniofacial osteogenesis, endochondral ossification is an essential process for the development and elongation of the appendicular bones. Undisputedly, the epiphyseal plate is frequently subject to pathologic anomalies of skeletal growth and development. ...
NELL‐1, an osteoinductive protein, has been shown to regulate skeletal ossification. Interestingly, an interstitial 11p14.1‐p15.3 deletion involving the Nell‐1 gene was recently reported in a patient with short stature and delayed fontanelle closure. Here we sought to define the role of Nell‐1 in endochondral ossification by investigating Nell‐1‐specific inactivation in Col2α1 expressing cell lineages. Nell‐1flox/flox; Col2α1‐Cre+ (Nell‐1Col2α1KO) mice were generated for comprehensive analysis. Nell‐1Col2α1KO mice were born alive but displayed subtle femoral length shortening. At 1 and 3 months postpartum, Nell‐1 inactivation resulted in dwarfism and premature osteoporotic phenotypes. Specifically, Nell‐1Col2α1KO femurs and tibias exhibited significantly reduced length, BMD, BV/TV, trabecular number/thickness, cortical volume/thickness/density, and increased trabecular separation. The decreased bone formation rate revealed by dynamic histomorphometry was associated with altered numbers and/or function of osteoblasts and osteoclasts. Furthermore, longitudinal observations by in vivo micro‐CT showed delayed and reduced mineralization at secondary ossification centers in mutants. Histologically, reduced staining intensities of Safranin O, Col‐2, Col‐10, and fewer BrdU‐positive chondrocytes were observed in thinner Nell‐1Col2α1KO epiphyseal plates along with altered distribution and weaker expression level of Ihh, Patched‐1, PTHrP, and PTHrP receptor. Primary Nell‐1Col2α1KO chondrocytes also exhibited decreased proliferation and differentiation, and its downregulated expression of the Ihh‐PTHrP signaling molecules can be partially rescued by exogenous Nell‐1 protein. Moreover, intra‐nuclear Gli‐1 protein and gene expression of the Gli‐1 downstream target genes, Hip‐1 and N‐Myc, were also significantly decreased with Nell‐1 inactivation. Notably, the rescue effects were diminished/reduced with application of Ihh signaling inhibitors, cyclopamine or GANT61. Taken together, these findings suggest that Nell‐1 is a pivotal modulator of epiphyseal homeostasis and endochondral ossification. The cumulative chondrocyte‐specific Nell‐1 inactivation significantly impedes appendicular skeletogenesis resulting in dwarfism and premature osteoporosis through inhibiting Ihh signaling and predominantly altering the Ihh‐PTHrP feedback loop. This article is protected by copyright. All rights reserved
... Multiple NTDs within one embryo therefore would indicate that multiple sites of fusion must be present. However, in several studies it was found that neural tube defects are in fact not caused by failure of fusion but by reopening of the fused neural tube walls (Huang et al., 2002;Zhang et al., 2006). It seems that excessive apoptosis can cause reopening of the fused neural walls, which would make the presence of multiple defects still compatible with the single site closure theory. ...
Introduction Since the multi-site closure theory was first proposed in 1991 as explanation for the preferential localizations of neural tube defects, the closure of the neural tube has been debated. Although the multi-site closure theory is much cited in clinical literature, single-site closure is most apparent in literature concerning embryology. Inspired by Victor Hamburgers (1900-2001) statement that "our real teacher has been and still is the embryo, who is, incidentally, the only teacher who is always right", we decided to critically review both theories of neural tube closure. Materials and Methods To verify the theories of closure, we studied serial histological sections of 10 mouse embryos between 8.5 and 9.5 days of gestation and 18 human embryos of the Carnegie collection between Carnegie stage 9 (19-21 days) and 13 (28-32 days). Neural tube closure was histologically defined by the neuroepithelial remodeling of the two adjoining neural fold tips in the midline. Results We did not observe multiple fusion sites in neither mouse nor human embryos. A meta-analysis of case reports on neural tube defects showed that defects can occur at any level of the neural axis. Conclusions Our data indicate that the human neural tube fuses at a single site and, therefore, we propose to reinstate the single-site closure theory for neural tube closure. We showed that neural tube defects are not restricted to a specific location, thereby refuting the reasoning underlying the multi-site closure theory. This article is protected by copyright. All rights reserved.
... 13 In addition, application of Nell-1 induces hyaline cartilage regeneration, as demonstrated in a rabbit knee subchondral defect model, 14 and administration of Nell-1eoverexpressed bone marrow mesenchymal stem cells promotes articular cartilage reestablishment in critical-sized goat mandibular condyle osteochondral defects. 15 Developmentally, in comparison with wild-type (WT) littermates, newborn Nell-1 overexpression transgenic mice exhibit premature hypertrophy and apoptosis in the chondrocranium region, 16 whereas neonatal Nell-1edeficient mice have shorter and deformed rib cages and vertebral bodies with compressed intervertebral spaces accompanied with reduced cartilage extracellular matrix. 17 Moreover, Nell-1 deficiency also results in reduced expression of multiple cartilage-related genes. ...
Recent studies indicate that neural EGFL-like 1 (Nell-1), a secretive extracellular matrix molecule, is involved in chondrogenic differentiation. Herein, we demonstrated that Nell-1 serves as a key downstream target of runt-related transcription factor 2 (Runx2), a central regulator of chondrogenesis. Unlike in osteoblast lineage cells where Nell-1 and Runx2 demonstrate mutual regulation, further studies in chondrocytes revealed that Runx2 tightly regulates the expression of Nell-1; however, Nell-1 does not alter the expression of Runx2. More important, Nell-1 administration partially restored Runx2 deficiency-induced impairment of chondrocyte differentiation and maturation in vitro, ex vivo, and in vivo. Mechanistically, although the expression of Nell-1 is highly reliant on Runx2, the prochondrogenic function of Nell-1 persisted in Runx2(-/-) scenarios. The biopotency of Nell-1 is independent of the nuclear import and DNA binding functions of Runx2 during chondrogenesis. Nell-1 is a key functional mediator of chondrogenesis, thus opening up new possibilities for the application of Nell-1 in cartilage regeneration.
... Protein kinase C-binding protein Nel-like molecule-1 (NELL-1) is a growth factor originally identified in patients with craniosyntosis [59]. Since its discovery, animal studies involving overexpression as well as deficiency have confirmed its importance in bone formation [60][61][62][63]. Investigators have attempted to utilize the osteoinductive effects of NELL-1 to enhance bone repair in experimental animal models. ...
Normal bone healing is a complex process that eventually restores original structure and function to the site of trauma. However, clinical circumstances such as nonunion, critical-sized defects, systemic bone disease, and fusion procedures have stimulated a search for ways to enhance this normal healing process. Biologics are an important part of this search and many, including bone marrow aspirate concentrate, demineralized bone matrix, platelet-rich plasma, bone morphogenic proteins, and platelet-derived growth factor, are currently in clinical use. Many others, including mesenchymal stem cells, parathyroid hormone, and Nel-like molecule-1 (NELL-1) will likely be in use in the future depending on the results of preclinical and clinical trials.
Nel-like molecule-1 (Nell-1) is a recently discovered secreted protein that plays an important role in osteoblast differentiation, bone formation, and bone regeneration. However, its expression and distribution during tooth development are largely unknown. The aim of this study was to investigate the expression patterns of Nell-1 during murine molar development by immunohistochemistry. Nell-1 protein was expressed during molar development in embryonic and postnatal Kunming mice, but its expression levels and patterns at various developmental stages differed. At embryonic day 13.5 (E13.5) and E14.5, Nell-1 was found in both the entire enamel organ and the underlying mesenchyme. At E16.5, it was detected in the inner and outer enamel epithelia, stratum intermedium, secondary enamel knot, and dental papilla. At E18.5, Nell-1 was expressed in the differentiating ameloblasts, differentiating odontoblasts, and stratum intermedium. Positive staining was also found in the outer enamel epithelium. At postnatal day 2.5 (P2.5), P5, and P7, Nell-1 appeared in the secretory and mature ameloblasts and odontoblasts (odontoblastic bodies and processes) as well as immature enamel. Hertwig's epithelial root sheath also stained positively at P7. At P13.5, positive staining was restricted to the reduced dental epithelium and odontoblasts, whereas Nell-1 disappeared in the mature enamel. During tooth eruption, Nell-1 was observed only in the odontoblastic bodies, odontoblastic processes, and endothelial cells of blood vessels. The spatiotemporal expression patterns of Nell-1 during murine tooth development suggest that it might play an important role in ameloblast and odontoblast differentiation, secretion and mineralization of the extracellular enamel matrix, molar crown morphogenesis, as well as root formation.
The shape of the embryonic ectoderm of early post-implantation mouse embryos changes greatly in the period of 6·2–7·3 days post coitum. The subcellular morphology of the embryonic ectoderm remains unchanged, except in the primitive-streak region. Cell kinetics differ between ectodermal regions. These differences may be related to the changes in the shape of the ectoderm. The increase in cell number in the lateral ectoderm (the prospective surface ectoderm) exceeds that in the frontal ectoderm (the future neurectoderm). This is not due to differences in the duration of the cell cycle. It can be explained, however, by the occurrence of different relative numbers of dividing and non-dividing cells. These numbers vary between the two regions. The percentage of non-dividing cells in the frontal ectoderm may reach 45, whereas in the lateral ectoderm this percentage is not higher than 15. Autoradiography in tritiated thymidine-treated embryos combined with the mitotic indices gave us all of the parameters necessary to present a model capable of clarifying the growth of the ectoderm during gastrulation, as well as the changes in the shape of the ectoderm.
The Fas antigen (Fas) belongs to the tumor necrosis factor (TNF)/nerve growth factor receptor family, and it mediates apoptosis. Using a soluble form of mouse Fas, prepared by fusion with human immunoglobulin Fc, Fas ligand was detected on the cell surface of a cytotoxic T cell hybridoma, PC60-d10S. A cell population that highly expresses Fas ligand was sorted using a fluorescence-activated cell sorter, and its cDNA was isolated from the sorted cells by expression cloning. The amino acid sequence indicated that Fas ligand is a type II transmembrane protein that belongs to the TNF family. The recombinant Fas ligand expressed in COS cells induced apoptosis in Fas-expressing target cells. Northern hybridization revealed that Fas ligand is expressed in activated splenocytes and thymocytes, consistent with its involvement in T cell-mediated cytotoxicity and in several nonlymphoid tissues, such as testis.
Neural crest cells are multipotential stem cells that contribute extensively to vertebrate development and give rise to various cell and tissue types. Determination of the fate of mammalian neural crest has been inhibited by the lack of appropriate markers. Here, we make use of a two-component genetic system for indelibly marking the progeny of the cranial neural crest during tooth and mandible development. In the first mouse line, Cre recombinase is expressed under the control of the Wnt1 promoter as a transgene. Significantly, Wnt1 transgene expression is limited to the migrating neural crest cells that are derived from the dorsal CNS. The second mouse line, the ROSA26 conditional reporter (R26R), serves as a substrate for the Cre-mediated recombination. Using this two-component genetic system, we have systematically followed the migration and differentiation of the cranial neural crest (CNC) cells from E9.5 to 6 weeks after birth. Our results demonstrate, for the first time, that CNC cells contribute to the formation of condensed dental mesenchyme, dental papilla, odontoblasts, dentine matrix, pulp, cementum, periodontal ligaments, chondrocytes in Meckel's cartilage, mandible, the articulating disc of temporomandibular joint and branchial arch nerve ganglia. More importantly, there is a dynamic distribution of CNC- and non-CNC-derived cells during tooth and mandibular morphogenesis. These results are a first step towards a comprehensive understanding of neural crest cell migration and differentiation during mammalian craniofacial development. Furthermore, this transgenic model also provides a new tool for cell lineage analysis and genetic manipulation of neural-crest-derived components in normal and abnormal embryogenesis.
For decades, Emery and Rimoin's Principles and Practice of Medical Genetics has provided the ultimate source for practicing clinicians to learn how the study of genetics can be integrated into practice. With almost 5,000 pages of detailed coverage, this fully online 6th edition of the classic reference details a complete picture of the growing field for medical students, residents and physicians involved in the care of patients with genetic conditions. Clinically oriented information is supported by expanded sections on basic principles of genetics, research approaches, and analytics to embrace the evolving population of students, researchers, and practitioners who are integrating their work to provide advanced diagnosis, prevention and treatment of human disease. With advances in high-throughput technologies propelling the closer integration of lab and clinical work, this edition bridges the gap between high-level molecular genetics and clinical application. Features 174 review-length contributions that encompass traditional and new areas of the field - including in cancer genetics, genomic technologies, and molecular assays Provides many thousands of pertinent literature references guiding the reader in identifying related topics Fully illustrated with hundreds of colour images, supporting identification, concept illustration and method processing.
The spatial and temporal aspects of cranial neural crest cell migration in the mouse are poorly understood because of technical limitations. No reliable cell markers are available and vital staining of embryos in culture has had limited success because they develop normally for only 24 hours. Here, we circumvent these problems by combining vital dye labelling with exo utero embryological techniques. To define better the nature of cranial neural crest cell migration in the mouse embryo, premigratory cranial neural crest cells were labelled by injecting DiI into the amniotic cavity on embryonic day 8. Embryos, allowed to develop an additional 1 to 5 days exo utero in the mother before analysis, showed distinct and characteristic patterns of cranial neural crest cell migration at the different axial levels. Neural crest cells arising at the level of the forebrain migrated ventrally in a contiguous stream through the mesenchyme between the eye and the diencephalon. In the region of the midbrain, the cells migrated ventrolaterally as dispersed cells through the mesenchyme bordered by the lateral surface of the mesencephalon and the ectoderm. At the level of the hindbrain, neural crest cells migrated ventrolaterally in three subectodermal streams that were segmentally distributed. Each stream extended from the dorsal portion of the neural tube into the distal portion of the adjacent branchial arch. The order in which cranial neural crest cells populate their derivatives was determined by labelling embryos at different stages of development. Cranial neural crest cells populated their derivatives in a ventral-to-dorsal order, similar to the pattern observed at trunk levels. In order to confirm and extend the findings obtained with exo utero embryos, DiI (1,1-dioctadecyl-3,3,3′,3′-tetramethylindo-carbocyanine perchlorate) was applied focally to the neural folds of embryos, which were then cultured for 24 hours. Because the culture technique permitted increased control of the timing and location of the DiI injection, it was possible to determine the duration of cranial neural crest cell emigration from the neural tube. Cranial neural crest cell emigration from the neural folds was completed by the 11-somite stage in the region of the rostral hindbrain, the 14-somite stage in the regions of the midbrain and caudal hindbrain and not until the 16-somite stage in the region of the forebrain. At each level, the time between the earliest and latest neural crest cells to emigrate from the neural tube appeared to be 9 hours.
Human embryos and fetuses (n=25) ranging from 12 to 117 mm CRL (crown-rump-length) were serially sectioned and the mandibles were reconstructed in 3D. In addition, characteristic areas of apposition, resorption and resting zones were projected onto the surface of the mandibular reconstructions after histological evaluation of the remodeling processes. Furthermore, morphometric data were taken to describe growth processes in horizontal views. In this way the changing outlines as seen in 3D could be correlated with the remodeling patterns and with the changes in growth. In these stages the mandible showed a general appositional growth, but resorption areas were found at the posterior margins of the mental foramen and at the lateral and medial posterior bony planes at concave surfaces. The bulging of bone underneath and over Meckel's cartilage could be recognized as active appositional growth areas. Meckel's cartilage itself lay in a trough which could be characterized by less apposition and even resorption. Questions were raised in how much the gap between our present knowledge of genetic expression of signaling molecules and the precise morphologic description of the mandibles can be bridged.