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In mammalian male gametogenesis the sex chromosomes are distinctive in both gene activity and epigenetic strategy. At first meiotic prophase the heteromorphic X and Y chromosomes are placed in a separate chromatin domain called the XY body. In this process, X,Y chromatin becomes highly phosphorylated at S139 of H2AX leading to the repression of gonosomal genes, a process known as meiotic sex chromosome inactivation (MSCI), which has been studied best in mice. Post-meiotically this repression is largely maintained. Disturbance of MSCI in mice leads to harmful X,Y gene expression, eventuating in spermatocyte death and sperm heterogeneity. Sperm heterogeneity is a characteristic of the human male. For this reason we were interested in the efficiency of MSCI in human primary spermatocytes. We investigated MSCI in pachytene spermatocytes of seven probands: four infertile men and three fertile controls, using direct and indirect in situ methods. A considerable degree of variation in the degree of MSCI was detected, both between and within probands. Moreover, in post-meiotic stages this variation was observed as well, indicating survival of spermatocytes with incompletely inactivated sex chromosomes. Furthermore, we investigated the presence of H3K9me3 posttranslational modifications on the X and Y chromatin. Contrary to constitutive centromeric heterochromatin, this heterochromatin marker did not specifically accumulate on the XY body, with the exception of the heterochromatic part of the Y chromosome. This may reflect the lower degree of MSCI in man compared to mouse. These results point at relaxation of MSCI, which can be explained by genetic changes in sex chromosome composition during evolution and candidates as a mechanism behind human sperm heterogeneity. 相似文献
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Molecular aspects of XY body formation 总被引:1,自引:0,他引:1
Hoyer-Fender S 《Cytogenetic and genome research》2003,103(3-4):245-255
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Turner JM Mahadevaiah SK Benavente R Offenberg HH Heyting C Burgoyne PS 《Chromosoma》2000,109(6):426-432
During male meiosis in mammals the X and Y chromosomes become condensed to form the sex body (XY body), which is the morphological manifestation of the process of meiotic sex chromosome inactivation (MSCI). An increasing number of sex body located proteins are being identified, but their functions in relation to MSCI are unclear. Here we demonstrate that assaying male sex body located proteins during XY female mouse meiosis, where MSCI does not take place, is one way in which to begin to discriminate between potential functions. We show that a newly identified protein, "Asynaptin" (ASY), detected in male meiosis exclusively in association with the X and Y chromatin of the sex body, is also expressed in pachytene oocytes of XY females where it coats the chromatin of the asynapsed X in the absence of MSCI. Furthermore, in pachytene oocytes of females carrying a reciprocal autosomal translocation, ASY associates with asynapsed autosomal chromatin. Thus the location of ASY to the sex body during male meiosis is likely to be a response to the asynapsis of the non-homologous regions [outside the pseudoautosomal region (PAR)] of the heteromorphic X-Y bivalent, rather than being related to MSCI. In contrast to ASY, the previously described sex body protein XY77 proved to be male sex body specific. Potential functions for MSCI and the sex body are discussed together with the possible roles of these two proteins. 相似文献
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Namekawa SH Park PJ Zhang LF Shima JE McCarrey JR Griswold MD Lee JT 《Current biology : CB》2006,16(7):660-667
In mammals, the X and Y chromosomes are subject to meiotic sex chromosome inactivation (MSCI) during prophase I in the male germline, but their status thereafter is currently unclear. An abundance of X-linked spermatogenesis genes has spawned the view that the X must be active . On the other hand, the idea that the imprinted paternal X of the early embryo may be preinactivated by MSCI suggests that silencing may persist longer . To clarify this issue, we establish a comprehensive X-expression profile during mouse spermatogenesis. Here, we discover that the X and Y occupy a novel compartment in the postmeiotic spermatid and adopt a non-Rabl configuration. We demonstrate that this postmeiotic sex chromatin (PMSC) persists throughout spermiogenesis into mature sperm and exhibits epigenetic similarity to the XY body. In the spermatid, 87% of X-linked genes remain suppressed postmeiotically, while autosomes are largely active. We conclude that chromosome-wide X silencing continues from meiosis to the end of spermiogenesis, and we discuss implications for proposed mechanisms of imprinted X-inactivation. 相似文献
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Royo H Polikiewicz G Mahadevaiah SK Prosser H Mitchell M Bradley A de Rooij DG Burgoyne PS Turner JM 《Current biology : CB》2010,20(23):2117-2123
The mammalian X and Y chromosomes share little homology and are largely unsynapsed during normal meiosis. This asynapsis triggers inactivation of X- and Y-linked genes, or meiotic sex chromosome inactivation (MSCI). Whether MSCI is essential for male meiosis is unclear. Pachytene arrest and apoptosis is observed in mouse mutants in which MSCI fails, e.g., Brca1(-/-), H2afx(-/-), Sycp1(-/-), and Msh5(-/-). However, these also harbor defects in synapsis and/or recombination and as such may activate a putative pachytene checkpoint. Here we present evidence that MSCI failure is sufficient to cause pachytene arrest. XYY males exhibit Y-Y synapsis and Y chromosomal escape from MSCI without accompanying synapsis/recombination defects. We find that XYY males, like synapsis/recombination mutants, display pachytene arrest and that this can be circumvented by preventing Y-Y synapsis and associated Y gene expression. Pachytene expression of individual Y genes inserted as transgenes on autosomes shows that expression of the Zfy 1/2 paralogs in XY males is sufficient to phenocopy the pachytene arrest phenotype; insertion of Zfy 1/2 on the X chromosome where they are subject to MSCI prevents this response. Our findings show that MSCI is essential for male meiosis and, as such, provide insight into the differential severity of meiotic mutations' effects on male and female meiosis. 相似文献
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Pairing of the sex chromosomes during mammalian meiosis is characterized by the formation of a unique heterochromatin structure
at the XY body. The mechanisms underlying the formation of this nuclear domain are reportedly highly conserved from marsupials
to mammals. In this study, we demonstrate that in contrast to all eutherian species studied to date, partial synapsis of the
heterologous sex chromosomes during pachytene stage in the horse is not associated with the formation of a typical macrochromatin
domain at the XY body. While phosphorylated histone H2AX (γH2AX) and macroH2A1.2 are present as a diffuse signal over the
entire macrochromatin domain in mouse pachytene spermatocytes, γH2AX, macroH2A1.2, and the cohesin subunit SMC3 are preferentially
enriched at meiotic sex chromosome cores in equine spermatocytes. Moreover, although several histone modifications associated
with this nuclear domain in the mouse such as H3K4me2 and ubH2A are conspicuously absent in the equine XY body, prominent
RNA polymerase II foci persist at the sex chromosomes. Thus, the localization of key marker proteins and histone modifications
associated with the XY body in the horse differs significantly from all other mammalian systems described. These results demonstrate
that the epigenetic landscape and heterochromatinization of the equine XY body might be regulated by alternative mechanisms
and that some features of XY body formation may be evolutionary divergent in the domestic horse. We propose equine spermatogenesis
as a unique model system for the study of the regulatory networks leading to the epigenetic control of gene expression during
XY body formation. 相似文献
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Structure and pairing behavior of sex chromosomes in females of four T(W;Z) lines of the Mediterranean flour moth, Ephestia kuehniella, were investigated using light and electron microscopic techniques and compared with the wild type. In light microscopic preparations of pachytene oocytes of wild-type females, the WZ bivalent stands out by its heterochromatic W chromosome strand. In T(W;Z) females, the part of the Z chromosome that was translated onto the W chromosome was demonstrated as a distal segment of the neo-W chromosome, displaying a characteristic non-W chromosomal chromomere-interchromomere pattern. This segment is homologously paired with the corresponding part of a complete Z chromosome. In contrast with the single ball of heterochromatic W chromatin in highly polyploid somatic nuclei of wild-type females, the translocation causes the formation of deformed or fragmented W chromatin bodies, probably owing to opposing tendencies of the Z and W chromosomal parts of the neo-W. In electron microscopic preparations of microspread nuclei, sex chromosome bivalents were identified by the remnants of electron-dense heterochromatin tangles decorating the W chromosome axis, by the different lengths of the Z and W chromosome axes, and by incomplete pairing. No heterochromatin tangles were attached to the translocated segment of the Z chromosome at one end of the neo-W chromosome. Because of the homologous pairing between the translocation and the structurally normal Z chromosome, pairing affinity of sex chromosomes in T(W;Z) females is significantly improved. Specific differences observed among T(W;Z)1-4 translocations are probably due to the different lengths of the translocated segments. 相似文献
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The chromatin organization in developing germ cells of Drosophila hydei males was studied with the highly sensitive DNA stain DAPI (4, 6-diamidino-2-phenylindole dichloride). The prophase of meiosis I is characterized by decondensed chromosomes and only late during this stage do they condense rapidly. The sex chromosomes show allocycly. During postmeiotic development the final condensation of chromatin is preceded by a cycle of condensation and subsequent decondensation. Meiotic chromosomes were studied in more detail after orcein staining. Pairing sites of the sex chromosomes could be localized in the distal end of the heterochromatic arm of the X chromosome and distally in both arms of the Y chromosome. The various heterochromatic parts of the genome condense differentially in meiosis. Chromatin reorganization was studied cytochemically with antibodies raised against histones H1 and H2A of D. melanogaster. The core histone H2A is present in spermatid nuclei until the late elongation stage. However, histone H1 is not found in the chromatin later than the early primary spermatocyte stage. Thus, chromatin reorganization during spermatogenesis in D. hydei is complex. The process is discussed with regard to possible functions. 相似文献
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Sam Schoenmakers Evelyne Wassenaar Joop S. E. Laven J. Anton Grootegoed Willy M. Baarends 《Chromosoma》2010,119(3):311-324
During male meiotic prophase in mammals, X and Y are in a largely unsynapsed configuration, which is thought to trigger meiotic
sex chromosome inactivation (MSCI). In avian species, females are ZW, and males ZZ. Although Z and W in chicken oocytes show
complete, largely heterologous synapsis, they too undergo MSCI, albeit only transiently. The W chromosome is already inactive
in early meiotic prophase, and inactive chromatin marks may spread on to the Z upon synapsis. Mammalian MSCI is considered
as a specialised form of the general meiotic silencing mechanism, named meiotic silencing of unsynapsed chromatin (MSUC).
Herein, we studied the avian form of MSUC, by analysing the behaviour of the peculiar germline restricted chromosome (GRC)
that is present as a single copy in zebra finch spermatocytes. In the female germline, this chromosome is present in two copies,
which normally synapse and recombine. In contrast, during male meiosis, the single GRC is always eliminated. We found that
the GRC in the male germline is silenced from early leptotene onwards, similar to the W chromosome in avian oocytes. The GRC
remains largely unsynapsed throughout meiotic prophase I, although patches of SYCP1 staining indicate that part of the GRC
may self-synapse. In addition, the GRC is largely devoid of meiotic double strand breaks. We observed a lack of the inner
centromere protein INCENP on the GRC and elimination of the GRC following metaphase I. Subsequently, the GRC forms a micronucleus
in which the DNA is fragmented. We conclude that in contrast to MSUC in mammals, meiotic silencing of this single chromosome
in the avian germline occurs prior to, and independent of DNA double strand breaks and chromosome pairing, hence we have named
this phenomenon meiotic silencing prior to synapsis (MSPS). 相似文献
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Cabrero J Teruel M Carmona FD Jiménez R Camacho JP 《Cytogenetic and genome research》2007,119(1-2):135-142
The facultative heterochromatic X chromosome in leptotene spermatocytes of the grasshopper Eyprepocnemis plorans showed marked hypoacetylation for lysine 9 in the H3 histone (H3-K9) with no sign of histone H2AX phosphorylation. Since H3-K9 hypoacetylation precedes the meiotic appearance of phosphorylated H2AX (gamma-H2AX), which marks the beginning of recombinational DNA double-strand breaks (DSBs), it seems that meiotic sex-chromosome inactivation (MSCI) in this grasshopper occurs prior to the beginning of recombination and hence synapsis (which in this species begins later than recombination). In addition, all constitutively heterochromatic chromosome regions harbouring a 180-bp tandem-repeat DNA and rDNA (B chromosomes and pericentromeric regions of A chromosomes) were H3-K9 hypoacetylated at early leptotene even though they will synapse at subsequent stages. This also suggests that meiotic silencing in this grasshopper might be independent of synapsis. The H3-K9 hypoacetylated state of facultative and constitutive heterochromatin persisted during subsequent meiotic stages and was even apparent in round spermatids. Finally, the fact that B chromosomes are differentially hypoacetylated in testis and embryo interphase cells suggests that they might be silenced early in development and remain this way for most (or all) life-cycle stages. 相似文献
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Meiotic sex chromosome inactivation 总被引:12,自引:0,他引:12
Turner JM 《Development (Cambridge, England)》2007,134(10):1823-1831
X chromosome inactivation is most commonly studied in the context of female mammalian development, where it performs an essential role in dosage compensation. However, another form of X-inactivation takes place in the male, during spermatogenesis, as germ cells enter meiosis. This second form of X-inactivation, called meiotic sex chromosome inactivation (MSCI) has emerged as a novel paradigm for studying the epigenetic regulation of gene expression. New studies have revealed that MSCI is a special example of a more general mechanism called meiotic silencing of unsynapsed chromatin (MSUC), which silences chromosomes that fail to pair with their homologous partners and, in doing so, may protect against aneuploidy in subsequent generations. Furthermore, failure in MSCI is emerging as an important etiological factor in meiotic sterility. 相似文献