Fig. 3.

The role of SPPL2c in the murine testis. SPPL2c shows selective expression in elongated spermatids. In these cells, SPPL2c resides in the endoplasmic reticulum (ER). Two in vivo substrates of this protease have been identified: the SNARE protein syntaxin 8 (Stx8) and Phospholamban (PLN), an interactor and inhibitor of the SERCA Ca²⁺ ATPase. Both proteins accumulate in the testis of SPPL2c-deficient mice. As functional consequences of SPPL2c-deficiency, handling of Ca²⁺ and membrane trafficking in the secretory pathway are altered in spermatids. SPPL2c^−/− spermatids show a reduced cytoplasmic Ca²⁺ concentration. Furthermore, the organisation of the Golgi apparatus is less compact which may have implications for the protein delivery to the forming acrosome. Mature SPPL2c^−/− sperm cells show an altered glycosylation pattern presumably reflecting alterations of glycosyltransferase trafficking which has been characterised in SPPL2c-overexpressing HEK cells