Loss of protein phosphatase 1cγ (PPP1CC) leads to impaired spermatogenesis associated with defects in chromatin condensation and acrosome development: an ultrastructural analysis

Abstract

Human male infertility affects w5% of men, with one-third suffering from testicular failure, likely the result of an underlying genetic abnormality that disrupts spermatogenesis during development. Mouse models of male infertility such as the Ppp1cc knockout mouse display very similar phenotypes to humans with testicular failure. Male Ppp1cc mutant mice are sterile due to disruptions in spermatogenesis that begin during prepubertal testicular development, and continue into adulthood, often resulting in loss of germ cells to the point of Sertoli cell-only syndrome. The current study employs light and electron microscopy to identify new morphological abnormalities in Ppp1cc mutant seminiferous epithelium. This study reveals that germ cells become delayed in their development around stages VII and VIII of spermatogenesis. Loss of these cells likely results in the reduced numbers of elongating spermatids and spermatozoa previously observed in mutant animals. Interestingly, Ppp1cc mutants also display reduced numbers of spermatogonia compared with their wild-type counterparts. Using electron microscopy, we have shown that junction complexes in Ppp1cc mutants are ultrastructurally normal, and therefore do not contribute to the breakdown in tissue architecture seen in mutants. Electron microscopy revealed major acrosomal and chromatin condensation defects in Ppp1cc mutants. Our observations are discussed in the context of known molecular changes in Ppp1cc mutant testes.

PPP1CC2 can form a kinase/phosphatase complex with the testis-specific proteins TSSK1 and TSKS in the mouse testis

“…Mouse spermatogenesis can be divided into 12 different stages that arise in a cyclical fashion in the seminiferous tubules (Russell et al 1990). It should be noted that the loss of Ppp1cc results in a bottleneck at stages VII/VIII of spermatogenesis, as well as a prominent loss of spermatids (Forgione et al 2010). In WT seminiferous tubules, the previously described punctate expression pattern was observed for TSKS (Fig.…”

“…However, the precise role in this process, particularly that of the testis-specific isoform PPP1CC2, remains unknown. The multitude of defects within the Ppp1cc mutant seminiferous epithelium suggests the possibility of pleiotropic functions, with defects in both meiotic and post-meiotic germ cells being evident (Varmuza et al 1999, Forgione et al 2010. In an effort to learn more about the function(s) of PPP1CC2 in spermatogenesis, we carried out GST pulldown assays to identify PPP1CC2-interacting proteins in the testis.…”

“…WT and Ppp1cc mutant testes were processed and analysed by electron microscopy (EM) as described previously (Forgione et al 2010). Tssk1/2 mutant testes were processed and analysed by EM as described previously (Shang et al 2010).…”

“…When Ppp1cc is deleted by targeted mutagenesis, the only observable phenotypic consequence is homozygous male infertility, due to a failure of spermatogenesis, reminiscent of the common human condition non-obstructive azoospermia (Varmuza et al 1999). Inside the seminiferous tubules, a widespread loss of germ cells is evident, most prominently in postmeiotic spermatids, leading to a breakdown of the spermatogenic cycle (Varmuza et al 1999, Forgione et al 2010). The few surviving germ cells feature a range of morphological abnormalities, including those involving meiosis, chromatin condensation, acrosome formation and mitochondrial organization (Varmuza et al 1999, Chakrabarti et al 2007, Forgione et al 2010.…”

“…Inside the seminiferous tubules, a widespread loss of germ cells is evident, most prominently in postmeiotic spermatids, leading to a breakdown of the spermatogenic cycle (Varmuza et al 1999, Forgione et al 2010). The few surviving germ cells feature a range of morphological abnormalities, including those involving meiosis, chromatin condensation, acrosome formation and mitochondrial organization (Varmuza et al 1999, Chakrabarti et al 2007, Forgione et al 2010. In the mouse testis, a number of different proteins have been shown to interact with PPP1CC2.…”