Loss of HR6B ubiquitin-conjugating activity results in damaged synaptonemal complex structure and increased crossing-over frequency during the male meiotic prophase.
The ubiquitin-conjugating enzymes HR6A and HR6B are the two mammalian homologs of Saccharomyces cerevisiae RAD6. In yeast, RAD6 plays an important role in postreplication DNA repair and in sporulation. HR6B knockout mice are viable, but spermatogenesis is markedly affected during postmeiotic steps, leading to male infertility. In the present study, increased apoptosis of HR6B knockout primary spermatocytes was detected during the first wave of spermatogenesis, indicating that HR6B performs a primary role during the meiotic prophase. Detailed analysis of HR6B knockout pachytene nuclei showed major changes in the synaptonemal complexes. These complexes were found to be longer. In addition, we often found depletion of synaptonemal complex proteins from near telomeric regions in the HR6B knockout pachytene nuclei. Finally, we detected an increased number of foci containing the mismatch DNA repair protein MLH1 in these nuclei, reflecting a remarkable and consistent increase (20 to 25%) in crossing-over frequency. The present findings reveal a specific requirement for the ubiquitin-conjugating activity of HR6B in relation to dynamic aspects of the synaptonemal complex and meiotic recombination in spermatocytes.
Baarends
Willy M
WM
Department of Reproduction and Development, Erasmus University Rotterdam, 3000 DR Rotterdam, The Netherlands. barrends@endov.fgg.eur.nl
Wassenaar
Evelyne
E
Hoogerbrugge
Jos W
JW
van Cappellen
Gert
G
Roest
Henk P
HP
Vreeburg
Jan
J
Ooms
Marja
M
Hoeijmakers
Jan H J
JH
Grootegoed
J Anton
JA
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002352:Carrier Proteins; D016923:Cell Death / Q000235:genetics; D003434:Crossing Over, Genetic; D004260:DNA Repair / Q000235:genetics; D008025:Ligases / Q000235:genetics / Q000378:metabolism*; D008297:Male; D008540:Meiosis; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D000070957:MutL Protein Homolog 1; D009154:Mutation; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins; D011418:Prophase / Q000235:genetics*; D013090:Spermatocytes / Q000502:physiology; D013573:Synaptonemal Complex / Q000235:genetics / Q000648:ultrastructure*; D016615:Telomere / Q000235:genetics / Q000378:metabolism; D013737:Testis / Q000166:cytology / Q000502:physiology; D025801:Ubiquitin / Q000378:metabolism; D044763:Ubiquitin-Conjugating Enzymes
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C501485:Mlh1 protein, mouse; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D025801:Ubiquitin; C512786:Ube2a protein, mouse; C465394:Ube2b protein, mouse; D044763:Ubiquitin-Conjugating Enzymes; D000070957:MutL Protein Homolog 1; D008025:Ligases