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Meiotic Consequences of Aneuploidy: Mouse Models of Down Syndrome

ABSTRACT: Aneuploidy, and especially the presence of unpaired chromosomal axes during meiosis, can cause infertility. However, it is not known if extra, unpaired autosomal chromosome segments acquire characteristic protein modifications and undergo transcriptional silencing (meiotic silencing of unpaired chromatin, or MSUC) similar to the unpaired regions of the X and Y chromosomes during spermatogenesis. We used three mouse models of Down syndrome, involving either an extra chromosome or translocation trisomy, to test requirements and consequences of meiotic protein modification and gene silencing in spermatocytes. These models reveal that copy number alone is not sufficient for up-regulation of genes in the trisomic interval, and that MSUC-promoting modifications are not sufficient for down-regulation of genes that reside in unpaired chromatin during meiosis. The position of a trisomic region relative to a centromere, the pairing status of the centromere, and the physical extent of the unpaired chromosomal region all affected assembly of meiotic protein modifications typical of MSUC. One key determinant to modification of unpaired chromatin and infertility in trisomy male mice appears to be proximity of unpaired chromatin to a centromere. Furthermore, the presence of an extra, unpaired centromere, but not translocation trisomy, causes global misregulation of transcription in spermatocytes. Thus, neither trisomy per se, nor chromatin modifications of unpaired chromosomal segments, have major effects on gene expression or meiotic success, but an intact unpaired chromosome has profoundly negative effects on meiotic gene expression.

ORGANISM(S): Mus musculus

PROVIDER: GSE13123 | GEO | 2008/10/11

SECONDARY ACCESSION(S): PRJNA109663

REPOSITORIES: GEO

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Project description:Dynamic nuclear architecture and chromatin organizations are the key features of the mid- prophase I in mammalian meiosis. Where the chromatin undergoes major changes, including meiosis-specific spatiotemporal arrangements and remodelling, the establishment of chromatin loop–axis structure, pairing, and crossing over between homologous chromosomes, any deficiencies in these events may induce genome instability, subsequently leading to failure to produce gametes and infertility. Despite the significance of chromatin structure, little is known about the location of chromatin marks and the necessity of their balance during meiosis prophase I. Here, we show a thorough cytological study of the surface-spread meiotic chromosomes of mouse spermatocytes for H3K9,14,18,23,27,36, H4K12,16 acetylation, and H3K4,9,27,36 methylation. Active acetylation and methylation marks on H3 and H4, such as H3K9ac, H3K14ac, H3K18ac, H3K36ac, H3K56ac, H4K12ac, H4K16ac, and H3K27me3 and H3K36me3 exhibited pan-nuclear localization away from heterochromatin. In comparison, repressive marks like H3K9me3 are localized to heterochromatin. In addition, we found that the intensities of H3K23ac, H3K27ac, and H3K9me3 enhanced during meiotic prophase I. Further, taking advantage of the delivery of small-molecule chemical inhibitors Methotrexate (MTX; heterochromatin enhancer), HMS-I1 (heterochromatin inhibitor), Anacardic acid (AA; histone acetyltransferase inhibitor), Trichostatin A (TSA; histone deacetylase inhibitor), IOX1 (JmjC demethylases inhibitor), and AZ505 (methyl transferase inhibitor) in seminiferous tubules through the rete testis route, revealed that alteration in histone modifications enhanced the centromere mislocalization, chromosome breakage, altered meiotic recombination and reduced sperm count. Notably, an imbalance in the histone modifications influences the chromosome axis length and chromatin loop size via transcriptional regulation of meiosis- specific genes. Our findings highlight the importance of balanced chromatin modifications in meiotic prophase I chromosome organization and instability.

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Meiotic Consequences of Aneuploidy: Mouse Models of Down Syndrome

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