t-SNARE Syntaxin2 (STX2) is implicated in intracellular transport of sulfoglycolipids during meiotic prophase in mouse spermatogenesis

Syntaxin2 (STX2), also known as epimorphin, is a member of the SNARE family of proteins, with expression in various types of cells. We previously identified an ENU-induced mutation, repro34, in the mouse Stx2 gene. The Stx2(repro34) mutation causes male-restricted infertility due to syncytial multinucleation of spermatogenic cells during meiotic prophase. A similar phenotype is also observed in mice with targeted inactivation of Stx2, as well as in mice lacking enzymes involved in sulfoglycolipid synthesis. Herein we analyzed expression and subcellular localization of STX2 and sulfoglycolipids in spermatogenesis. The STX2 protein localizes to the cytoplasm of germ cells at the late pachytene stage. It is found in a distinct subcellular pattern, presumably in the Golgi apparatus of pachytene/diplotene spermatocytes. Sulfoglycolipids are produced in the Golgi apparatus and transported to the plasma membrane. In Stx2(repro34) mutants, sulfoglycolipids are aberrantly localized in both pachytene/diplotene spermatocytes and in multinucleated germ cells. These results suggest that STX2 plays roles in transport and/or subcellular distribution of sulfoglycolipids. STX2 function in the Golgi apparatus and sulfoglycolipids may be essential for maintenance of the constriction between neighboring developing spermatocytes, which ensures ultimate individualization of germ cells in later stages of spermatogenesis.