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The sex chromosome pairing was normal in the 48, XYY, + sSMC patient. Early pachytene spermatocyte spreads from the control (a-b) and the patient (c-d) were immunostained for SYCP3 (red), MLH1 (green), and CREST (blue). Representative images of early pachytene spermatocytes showing associated (b
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Small supernumerary marker chromosomes (sSMCs) are structurally abnormal rare chromosomes, difficult to characterize by karyotyping, and have been associated with minor dysmorphic features, azoospermia, and recurrent miscarriages. However, sSMC with a gonosomal trisomy has never been reported. Spermatocyte spreading and immunostaining were applied...
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... ation and recombination between the sex chromosomes were also determined and compared with the control. In the patient, X-Y chromosomes were found to be asso- ciated in 83.7 % cells, while in 16.3 % spermatocytes, they were not associated. In control individuals, X and Y were associated in 80.4 % cells and were not associ- ated in 19.5 % cells (Fig. 3), which is not statistically different from the patient (P>0.05, chi-square test). In the patient, recombination between the sex chromo- somes (represented by MLH1 focus) was observed to be present always in the PAR1 region as in controls; however, it occurs in 57.5 % cells, which is significantly lower than that in control individuals ...
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... (1997) reported that a 47, XYY male with extremely low sperm count contained the extra Y in all the pachy- tene nuclei analyzed. Using immunocytogenetic tech- nique, we observed that only one Y chromosome was present in spermatocytes of the 48, XYY, +sSMC (Fig. 2). Moreover, the patient was normal for the pairing between the X and Y chromosomes (Fig. 3), although their recombination rate was lower in the pa- tient than in normal controls (Table ...
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... These sSMCs arise from the A chromosomes and are present in 1 out of 2300 newborns (Liehr and Weise 2007). Many are connected to specific syndromes, such as Emanuel, cat eye, and Pallister-Killian syndromes, or are associated with intellectual disabilities and infertility (Liehr 2012;Armanet et al. 2015;Jafari-Ghahfarokhi et al. 2015;Wang et al. 2015). Improved molecular characterization is beginning to reveal more about the genomic organization of supernumerary chromosomes (Breman et al. 2011;Sun et al. 2017). ...
In addition to a defined number of essential chromosomes, extra chromosomes called “B chromosomes” are present in roughly 15% of eukaryotic species. In this study, Hanlon et al. analyzed the recently discovered Drosophila melanogaster...
The number of chromosomes carried by an individual species is one of its defining characteristics. Some species, however, can also carry supernumerary chromosomes referred to as B chromosomes. B chromosomes were recently identified in a laboratory stock of Drosophila melanogaster—an established model organism with a wealth of genetic and genomic resources—enabling us to subject them to extensive molecular analysis. We isolated the B chromosomes by pulsed-field gel electrophoresis and determined their composition through next-generation sequencing. Although these B chromosomes carry no known euchromatic sequence, they are rich in transposable elements and long arrays of short nucleotide repeats, the most abundant being the uncharacterized AAGAT satellite repeat. Fluorescent in situ hybridization on metaphase chromosome spreads revealed this repeat is located on chromosome 4, strongly suggesting the origin of the B chromosomes is chromosome 4. Cytological and quantitative comparisons of signal intensity between chromosome 4 and the B chromosomes supports the hypothesis that the structure of the B chromosome is an isochromosome. We also report the identification of a new B chromosome variant in a related laboratory stock. This B chromosome has a similar repeat signature as the original but is smaller and much less prevalent. We examined additional stocks with similar genotypes and did not find B chromosomes, but did find these stocks lacked the AAGAT satellite repeat. Our molecular characterization of D. melanogaster B chromosomes is the first step toward understanding how supernumerary chromosomes arise from essential chromosomes and what may be necessary for their stable inheritance.
... The spermiogram of the carrier in a recent study showed OAT (oligoasthenoteratozoospermia) and seems to also confirm previous findings of the higher incidence of sSMC in males with decreased seminology 2,6,35,38,40 . Disruption of spermatogenesis may also occur when the sSMC associates with the bivalent XY, which may lead to a drop in semen parameters [40][41][42] . Kirkpatrick et al. 40 observed that sperm concentration was 10× decreased in a carrier of 46,XY,rob(13;21),+ mar when compared to a 45,XY,rob(13;21) without the Scientific RepoRts | 5:17408 | DOI: 10.1038/srep17408 marker chromosome. ...
Chromosomes occupy specific distinct areas in the nucleus of the sperm cell that may be altered in males with disrupted spermatogenesis. Here, we present alterations in the positioning of the human chromosomes 15, 18, X and Y between spermatozoa with the small supernumerary marker chromosome (sSMC; sSMC+) and spermatozoa with normal chromosome complement (sSMC−), for the first time described in the same ejaculate of an infertile, phenotypically normal male patient. Using classical and confocal fluorescent microscopy, the nuclear colocalization of chromosomes 15 and sSMC was analyzed. The molecular cytogenetic characteristics of sSMC delineated the karyotype as 47,XY,+der(15)(pter->p11.2::q11.1->q11.2::p11.2->pter)mat. Analysis of meiotic segregation showed a 1:1 ratio of sSMC+ to sSMC− spermatozoa, while evaluation of sperm aneuploidy status indicated an increased level of chromosome 13, 18, 21 and 22 disomy, up to 7 × (2.7 − 15.1). Sperm chromatin integrity assessment did not reveal any increase in deprotamination in the patient’s sperm chromatin. Importantly, we found significant repositioning of chromosomes X and Y towards the nuclear periphery, where both chromosomes were localized in close proximity to the sSMC. This suggests the possible influence of sSMC/XY colocalization on meiotic chromosome division, resulting in abnormal chromosome segregation, and leading to male infertility in the patient.
The number of chromosomes carried by an individual species is one of its defining characteristics. Some species, however, can also carry supernumerary chromosomes referred to as B chromosomes. B chromosomes were recently identified in a laboratory stock of Drosophila melanogaster — an established model organism with a wealth of genetic and genomic resources — enabling us to subject them to extensive molecular analysis. We isolated the B chromosomes by pulsed-field gel electrophoresis and determined their composition through next-generation sequencing. Although these B chromosomes carry no known euchromatic sequence, they are rich in transposable elements and long arrays of short nucleotide repeats, the most abundant being the uncharacterized AAGAT satellite repeat. Fluorescent in-situ hybridization on metaphase chromosome spreads revealed this repeat is located on Chromosome 4 , strongly suggesting the origin of the B chromosomes is Chromosome 4 . Cytological and quantitative comparisons of signal intensity between Chromosome 4 and the B chromosomes supports the hypothesis that the structure of the B chromosome is an isochromosome. We also report the identification of a new B chromosome variant in a related laboratory stock. This B chromosome has a similar repeat signature as the original but is smaller and much less prevalent. We examined additional stocks with similar genotypes and did not find B chromosomes, but did find these stocks lacked the AAGAT satellite repeat. Our molecular characterization of D. melanogaster B chromosomes is the first step towards understanding how supernumerary chromosomes arise from essential chromosomes and what may be necessary for their stable inheritance.
