Regulators of the protein phosphatase PP1γ2, PPP1R2, PPP1R7, and PPP1R11 are involved in epididymal sperm maturation

The serine/threonine protein phosphatase 1 (PP1) inhibitors PPP1R2, PPP1R7, and PPP1R11 are evolutionarily ancient and highly conserved proteins. Four PP1 isoforms, PP1 alpha, PP1 beta, PP1 gamma 1, and PP1 gamma 2, exist; three of them except PP1 gamma 2 are ubiquitous. The fact that PP1 gamma 2 isoform is present only in mammalian testis and sperm led to the notion that isoform-specific regulators for PP1 gamma 2 in sperm may be responsible for its function. In this report, we studied these inhibitors, PPP1R2, R7, and R11, to determine their spatial and temporal expression in testis and their regulatory functions in sperm. We show that, similar to PP1 gamma 2, the three inhibitors are expressed at high levels in developing spermatogenic cells. However, the transcripts for the regulators are expressed as unique sizes in testis compared with somatic tissues. The three regulators share localization with PP1 gamma 2 in the head and the principal piece of sperm. We show that the association of inhibitors to PP1 gamma 2 changes during epididymal sperm maturation. In immotile caput epididymal sperm, PPP1R2 and PPP1R7 are not bound to PP1 gamma 2, whereas in motile caudal sperm, all three inhibitors are bound as heterodimers or heterotrimers. In caudal sperm from male mice lacking sAC and glycogen synthase kinase 3, where motility and fertility are impaired, the association of PP1 gamma 2 to the inhibitors resembles immature caput sperm. Changes in the association of the regulators with PP1 gamma 2, due to their phosphorylation, are part of biochemical mechanisms responsible for the development of motility and fertilizing ability of sperm during their passage through the epididymis.