The ubiquitin-conjugating enzyme HR6B is required for maintenance of X chromosome silencing in mouse spermatocytes and spermatids.
BACKGROUND
The ubiquitin-conjugating enzyme HR6B is required for spermatogenesis in mouse. Loss of HR6B results in aberrant histone modification patterns on the trancriptionally silenced X and Y chromosomes (XY body) and on centromeric chromatin in meiotic prophase. We studied the relationship between these chromatin modifications and their effects on global gene expression patterns, in spermatocytes and spermatids.


RESULTS
HR6B is enriched on the XY body and on centromeric regions in pachytene spermatocytes. Global gene expression analyses revealed that spermatid-specific single- and multicopy X-linked genes are prematurely expressed in Hr6b knockout spermatocytes. Very few other differences in gene expression were observed in these cells, except for upregulation of major satellite repeat transcription. In contrast, in Hr6b knockout spermatids, 7298 genes were differentially expressed; 65% of these genes was downregulated, but we observed a global upregulation of gene transcription from the X chromosome. In wild type spermatids, approximately 20% of the single-copy X-linked genes reach an average expression level that is similar to the average expression from autosomes.


CONCLUSIONS
Spermatids maintain an enrichment of repressive chromatin marks on the X chromosome, originating from meiotic prophase, but this does not interfere with transcription of the single-copy X-linked genes that are reactivated or specifically activated in spermatids. HR6B represses major satellite repeat transcription in spermatocytes, and functions in the maintenance of X chromosome silencing in spermatocytes and spermatids. It is discussed that these functions involve modification of chromatin structure, possibly including H2B ubiquitylation.
Mulugeta Achame
Eskeatnaf
E
Department of Reproduction and Development Erasmus MC, Rotterdam, The Netherlands.
Wassenaar
Evelyne
E
Hoogerbrugge
Jos W
JW
Sleddens-Linkels
Esther
E
Ooms
Marja
M
Sun
Zu-Wen
ZW
van IJcken
Wilfred F J
WF
Grootegoed
J Anton
JA
Baarends
Willy M
WM
D000818:Animals; D018797:Cell Cycle Proteins / Q000235:genetics; D002503:Centromere / Q000235:genetics / Q000378:metabolism; D002843:Chromatin / Q000235:genetics / Q000378:metabolism; D018628:Gene Dosage / Q000235:genetics; D020869:Gene Expression Profiling; D055786:Gene Knockout Techniques; D050172:Genes, X-Linked / Q000235:genetics; D006657:Histones / Q000235:genetics / Q000378:metabolism; D008297:Male; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000235:genetics; D009928:Organ Specificity; D010750:Phosphoproteins / Q000235:genetics; D013087:Spermatids / Q000378:metabolism*; D013090:Spermatocytes / Q000378:metabolism*; D013737:Testis / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D044763:Ubiquitin-Conjugating Enzymes / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D054875:Ubiquitination; D015854:Up-Regulation; D014960:X Chromosome / Q000235:genetics* / Q000378:metabolism; D049951:X Chromosome Inactivation; D014998:Y Chromosome / Q000235:genetics
D018797:Cell Cycle Proteins; D002843:Chromatin; D006657:Histones; D008869:Microtubule-Associated Proteins; D010750:Phosphoproteins; C104434:spindlin; C512786:Ube2a protein, mouse; C465394:Ube2b protein, mouse; D044763:Ubiquitin-Conjugating Enzymes; C511160:UBR2 protein, mouse; D044767:Ubiquitin-Protein Ligases