Pachytene asynapsis drives meiotic sex chromosome inactivation and leads to substantial postmeiotic repression in spermatids.
Transcriptional silencing of the sex chromosomes during male meiosis (MSCI) is conserved among organisms with limited sex chromosome synapsis, including mammals. Since the 1990s the prevailing view has been that MSCI in mammals is transient, with sex chromosome reactivation occurring as cells exit meiosis. Recently, we found that any chromosome region unsynapsed during pachytene of male and female mouse meiosis is subject to transcriptional silencing (MSUC), and we hypothesized that MSCI is an inevitable consequence of this more general meiotic silencing mechanism. Here, we provide direct evidence that asynapsis does indeed drive MSCI. We also show that a substantial degree of transcriptional repression of the sex chromosomes is retained postmeiotically, and we provide evidence that this postmeiotic repression is a downstream consequence of MSCI/MSUC. While this postmeiotic repression occurs after the loss of MSUC-related proteins at the end of prophase, other histone modifications associated with transcriptional repression have by then become established.
Division of Developmental Genetics and Stem Cell Research, MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom. jturner@nimr.nrc.ac.uk
James M A
JM
Turner
Shantha K
SK
Mahadevaiah
Peter J I
PJ
Ellis
Michael J
MJ
Mitchell
Paul S
PS
Burgoyne
D000818:Animals; D005260:Female; D020868:Gene Silencing; D017404:In Situ Hybridization, Fluorescence / Q000379:methods; D008297:Male; D008540:Meiosis / Q000235:genetics*; D051379:Mice; D049471:Pachytene Stage / Q000235:genetics*; D012730:Sex Chromosomes / Q000235:genetics* / Q000378:metabolism; D013087:Spermatids / Q000166:cytology / Q000502:physiology*; D014158:Transcription, Genetic; D014960:X Chromosome / Q000235:genetics / Q000378:metabolism; D049951:X Chromosome Inactivation / Q000235:genetics; D014997:XYY Karyotype / Q000235:genetics; D014998:Y Chromosome / Q000235:genetics / Q000378:metabolism