STRA8-deficient spermatocytes initiate, but fail to complete, meiosis and undergo premature chromosome condensation.

We analysed the phenotypic outcome of a Stra8-null mutation on male meiosis. Because the mutant spermatocytes (1) underwent premeiotic DNA replication, (2) displayed cytological features attesting initiation of recombination and of axial-element assembly, and (3) expressed Spo11 and numerous other meiotic genes, it was concluded that STRA8 is dispensable for meiotic initiation. The few mutant spermatocytes that progressed beyond leptonema showed a prolonged bouquet-stage configuration, asynapsis and heterosynapsis, suggesting function(s) of STRA8 in chromosome pairing. Most importantly, a large number of mutant leptotene spermatocytes underwent premature chromosome condensation, within 24 hours following the meiotic S phase. This phenomenon yielded aberrant metaphase-like cells with 40 univalent chromosomes, similar to normal mitotic metaphases. From these latter observations and from the wild-type pattern of Stra8 expression, we propose that, in preleptotene spermatocytes, STRA8 is involved in the process that leads to stable commitment to the meiotic cell cycle.