The protein phosphatase 1 regulator NIPP1 is essential for mammalian spermatogenesis

Abstract

NIPP1 is one of the major nuclear interactors of protein phosphatase PP1. The deletion of NIPP1 in mice is early embryonic lethal, which has precluded functional studies in adult tissues. Hence, we have generated an inducible NIPP1 knockout model using a tamoxifen-inducible Cre recombinase transgene. The inactivation of the NIPP1 encoding alleles (Ppp1r8) in adult mice occurred very efficiently in testis and resulted in a gradual loss of germ cells, culminating in a Sertoli-cell only phenotype. Before the overt development of this phenotype Ppp1r8 −/− testis showed a decreased proliferation and survival capacity of cells of the spermatogenic lineage. A reduced proliferation was also detected after the tamoxifen-induced removal of NIPP1 from cultured testis slices and isolated germ cells enriched for undifferentiated spermatogonia, hinting at a testis-intrinsic defect. Consistent with the observed phenotype, RNA sequencing identified changes in the transcript levels of cell-cycle and apoptosis regulating genes in NIPP1-depleted testis. We conclude that NIPP1 is essential for mammalian spermatogenesis because it is indispensable for the proliferation and survival of progenitor germ cells, including (un)differentiated spermatogonia.

Functions and therapeutic potential of protein phosphatase 1: Insights from mouse genetics

“…In contrast, the liver-specific NIPP1 KO showed a rather mild phenotype associated with bile-duct hyperplasia through enhanced biliary epithelial cell proliferation [112]. Collectively, the NIPP1 mouse models indicate that the functions of NIPP1 may be cell-type dependent [107,108,112]. NIPP1-null embryos at embryonic day E6.5 showed increased global phospho-threonine signals [113], in line with a substrate-specifying role of NIPP1 (Table 3) [26,110].…”

“…NIPP1, encoded by the Ppp1r8 gene, is a major nuclear PIP that is ubiquitously expressed, but its expression level is cell-type dependent [107,108]. The N-terminal forkhead-associated domain of NIPP1 recruits PP1 substrates that are phosphorylated at threonine-proline dipeptide motifs, including the pre-mRNA splicing factor SAP155 and the methyltransferase EZH2 [38,94,109,110].…”

“…The global deletion of NIPP1 in mice resulted in early embryonic lethality associated with reduced cell proliferation (Table 3) [107]. Similarly, the postnatal tamoxifen-induced deletion of NIPP1 in the testis resulted in a progressive loss of germ cells, culminating in a Sertoli-cell-only phenotypes [108]. This can be attributed to the decreased proliferation and survival capacity of cells of the spermatogenic lineage.…”

The deletion of the protein phosphatase 1 regulator NIPP1 in testis causes hyperphosphorylation and degradation of the histone methyltransferase EZH2

“…The animals were sacrificed 2 weeks from the beginning of this treatment, when they reached the age of 6 weeks. At this stage, a histological phenotype cannot yet be discerned in the iKOs (27). However, the NIPP1 protein level in their testis was already reduced by about 70%, as compared with its level in CTR mice (Fig.…”

“…Using an inducible NIPP1 knockout (iKO) model, we have demonstrated that NIPP1 is essential for mammalian spermatogenesis and, more specifically, is required for the transcriptional regulation of genes implicated in germ cell proliferation and survival (27). In this study, we used this iKO model to show that the deletion of NIPP1 in testis is associated with the loss of EZH2 and a reduced histone H3K27 trimethylation at target genes.…”