INCREASED ACTIVITY ASSOCIATED WITH THE MAST205 PROTEIN-KINASE COMPLEXDURING MAMMALIAN SPERMIOGENESIS

The morphological and biochemical changes that occur in the haploid ma le germ cell during spermiogenesis facilitate the natural delivery of the paternally imprinted chromosomes into oocytes. Despite the obvious morphological changes, little is known about the molecular events und erlying spermiogenesis. We recently cloned a novel 205-kDa manchette m icrotubule-associated serine/threonine protein kinase (MAST205) from m ouse testis. The objective of this study was to further delineate the role of MAST205 in mammalian spermiogenesis. While MAST205 RNA levels were similar in pachytene spermatocytes, round spermatids, and residua l bodies, MAST205 protein could be detected only in round spermatids a nd residual bodies. Kinase activity associated with MAST205 immunoprec ipitates was low in pachytene spermatocytes, high in round spermatids, and maximal in residual bodies, indicating that MAST205-associated ki nase activity is modified during spermatid maturation. Furthermore, MA ST205 protein and the associated kinase activity were not detected in epididymal spermatozoa, indicating that MAST205 protein is either excl uded from, or degraded in, the latter cell type. Multiple heterologous protein species were seen in immunoprecipitates from S-35-labeled mou se seminiferous tubules using an affinity-purified MAST205 antiserum. Consistent with this observation, MAST205 eluted as part of a 1-2 x 10 (6) dalton protein complex when extracts of mouse testis were fraction ated by Superose 6 column chromatography. MAST205 mRNA was detected in human testis indicative of conservation in other mammalian species. T aken together, these results indicate that the MAST205 complex functio ns in spermatid maturation in mammals.