SPOC1 (PHF13) is required for spermatogonial stem cell differentiation and sustained spermatogenesis

Abstract

Summary SPOC1 (PHF13) is a recently identified protein that has been shown to dynamically associate with somatic chromatin, to modulate chromatin compaction and to be important for proper cell division. Here, we report on the expression of SPOC1 in promyelocytic leukaemia zinc finger (PLZF)-positive undifferentiated spermatogonial stem cells (SSCs) of the mouse testis. To investigate further the biological function of SPOC1 in germ cells we generated Spoc1 mutant mice from a gene-trap embryonic stem cell clone. Postpubertal homozygous Spoc1 2/2 animals displayed a pronounced progressive loss of germ cells from an initially normal germ epithelium of the testis tubules leading to testis hypoplasia. This loss first affected non-SSC stages of germ cells and then, at a later time point, the undifferentiated spermatogonia. Remarkably, successive loss of all germ cells (at .20 weeks of age) was preceded by a transient increase in the number of undifferentiated A aligned (A al ) spermatogonia in younger mice (at .10 weeks of age). The number of primary Spoc1 2/2 gonocytes, the proliferation of germ cells, and the initiation and progression of meiosis was normal, but we noted a significantly elevated level of apoptosis in the Spoc1 2/2 testis. Taken together, the data argue that SPOC1 is indispensable for stem cell differentiation in the testis and for sustained spermatogenesis.

SPOC1 modulates DNA repair by regulating key determinants of chromatin compaction and DNA damage response

“…In particular, both SPOC1 (4) and KAP-1 knockout (73) as well as a HP1-binding deficient KAP-1 mutant (74) all lead to progressive depletion of spermatogonial stem cells and their differentiated derivatives. The similar phenotypes of KAP-1 and SPOC1 knockout in testis argues for a cooperative physiological relationship in vivo in stem-cell maintenance and differentiation.…”

“…The ability of SPOC1 to associate with, and structurally alter chromatin depends on its plant homeodomain (PHD) (2), predicted to bind to H3K4me2/3 (3). In a mouse SPOC1 knockout model, SPOC1 protein expression was also recently shown to be indispensable for testis stem-cell differentiation and sustained spermatogenesis (4). These findings imply that SPOC1 plays a role in stem-cell maintenance, chromatin structure, and presumably also in oncogenesis.…”

Histone H3.3 regulates dynamic chromatin states during spermatogenesis

“…Notably, the majority of apoptotic events in null testes occurred in or around stage IX (supplementary material Fig. S2), a period where spermatogonia stem cells differentiating into spermatocytes cross the tightly regulated blood-testis barrier (BTB) (Bordlein et al, 2011;Cheng and Mruk, 2012;Morales et al, 2007;Mruk and Cheng, 2004;Oishi et al, 2004). Downregulated genes in null testes are expressed normally in spermatogonia, a cell type that in null mice also displayed increases in H3K9me3, indicating that an aberrant repressive chromatin state established in the early stages of null spermatogonia development might impede the expression of genes necessary for differentiation into pre-leptotene spermatocytes and the BTB transition.…”

PHF13: A new player involved in RNA polymerase II transcriptional regulation and co-transcriptional splicing

“…Knockout (KO) of either PHF13 or core PRC2 factors results in defects in stem cell differentiation and maintenance arguing for their importance in these state transitions. 20,21 Furthermore, PHF13 forms a common complex with H3K4me2/3, PRC2 and RNAPII S5P in mouse ESCs as was demonstrated by their co-elution and co-precipitation in column chromatography. 1 Consistently, PHF13 co-localized at a subset of PRC2 bound genes and its depletion led to increased expression from these bivalent targets, arguing that it acts as a transcriptional co-regulator at a subset of polycomb regulated genes.…”

“…RNAPII-mediated transcription is severely impaired in bivalent chromatin landscapes due to reduced histone acetylation 18 and the absence of the elongating S2P. 14 Coincidentally, PHF13 is highest expressed in stem cells, 20 where PRC2 repression of developmental promoters is important for pluripotency and likewise where PRC2-mediated repression of pluripotency factors is required for differentiation. Knockout (KO) of either PHF13 or core PRC2 factors results in defects in stem cell differentiation and maintenance arguing for their importance in these state transitions.…”