Primers used in this study.

Meiotic sex chromosome inactivation (MSCI) is an essential event in meiotic progression in mammalian spermatogenesis. We found that La Ribonucleoprotein 7 (LARP7) is involved in MSCI. LARP7 plays a role in fetal germ cells to promote their proliferation, but is once abolished in postnatal gonocytes and re-expressed in spermatocytes at the onset of meiosis. In spermatocytes, LARP7 localizes to the XY body, a compartmentalized chromatin domain on sex chromosomes. In germline-specific Larp7-deficient mice, spermatogenesis is arrested in spermatocytes, and transcription of the genes on sex chromosomes remained active, which suggests failure of meiotic sex chromosome inactivation (MSCI). Furthermore, the XY body in spermatocytes lacking Larp7 shows accumulation of H4K12ac and elimination of H3K9me2, suggesting defective chromatin silencing by abnormal epigenetic controls. These results indicate a new functional role for LARP7 in MSCI.