New candidate targets of protein phosphatase-1c-gamma-2 in mouse testis revealed by a differential phosphoproteome analysis

Reversible phosphorylation has been implicated in many developmental processes. Dephosphorylation is mediated by several families of phosphatases, including type 1 serine/threonine phosphatases (protein phosphatase-1 or PP1). The loss of the murine Ppp1cc gene causes male infertility as a result of impaired spermatogenesis. Ppp1cc encodes two splice isoforms, PPP1CC1 and PPP1CC2, with the latter being the most abundant isoform in the testis. However, the details of PPP1CC2's involvement in spermatogenesis are still unknown. As a phosphatase has been removed from the mutant mouse, a search for hyperphosphorylated proteins in the mutant testis may reveal the direct downstream targets of PPP1CC2. Using a whole tissue proteomics approach to identify testis-specific dephosphorylation targets of PPP1CC2, we found that two-dimensional electrophoresis identified 10 potential targets in the Ppp1cc null testis several of which are factors known to be important for spermatogenesis, such as HSPA2. Another potential target, tubulin, was found to be misregulated during Ppp1cc(-/-) spermatogenesis, disrupting manchette development. This work represents the first survey of the testicular phosphoproteome under pathological conditions.