Analysis of male meiotic "sex body" proteins during XY female meiosis provides new insights into their functions

During male meiosis in mammals the X and Y chromosomes become condensed to form the sex body (XY body), which is the morphological manifestation of th e process of meiotic sex chromosome inactivation (MSCI). An increasing numb er of sex body located proteins are being identified, but their functions i n relation to MSCI are unclear. Here we demonstrate that assaying male sex body located proteins during XY female mouse meiosis, where MSCI does not t ake place, is one way in which to begin to discriminate between potential f unctions. We show that a newly identified protein, "Asynaptin" (ASY), detec ted in male meiosis exclusively in association with the X and Y chromatin o f the sex body, is also expressed in pachytene oocytes of XY females where it coats the chromatin of the asynapsed X in the absence of MSCI. Furthermo re, in pachytene oocytes of females carrying a reciprocal autosomal translo cation, ASY associates with asynapsed autosomal chromatin. Thus the locatio n of ASY to the sex body during male meiosis is likely to be a response to the asynapsis of the non-homologous regions [outside the pseudoautosomal re gion (PAR)] of the heteromorphic X-Y bivalent, rather than being related to MSCI. In contrast to ASY, the pre viously described sex body protein XY77 proved to be male sex body specific. Potential functions for MSCI and the s ex body are discussed together with the possible roles of these two protein s.