A gene trap mutation of a murine homolog of the Drosophila stem cell factor Pumilio results in smaller testes but does not affect litter size or fertility

Abstract

Members of the Pumilio (also called PUF) gene family belong to a class of highly conserved developmental regulators that are present in both flies and humans. Much is known about the function of Pumilio genes in invertebrate development, in particular their role as stem cell factors required for maintenance and/or self-renewal of germline stem cells in Drosophila and Caenorhabditis elegans. It remains unknown whether Pumilio genes are also required for development in mammals; however, several lines of evidence suggest similar functions based on extensive sequence homology, similar RNA-binding properties to their invertebrate counterparts and well-documented interactions with germ cell factors required for fertility. Here we report characterization of a gene trap mutation that disrupts the mouse Pumilio-2 (Pum2) gene. Our data confirm that Pumilio-2 is expressed most abundantly in germ cells with the highest expression in undifferentiated gonocytes and spermatogonia. Furthermore, the mutation in Pum2 results in significantly smaller testes although the mutants are otherwise viable and fertile. In addition, we observed no stronger reproductive defects on a genetic background homozygous for a Pum2 null mutation and heterozygous for a Dazl mutation than Pum2 mutant alone. Thus, as in C. elegans where single members of the Pumilio gene family are dispensable for reproductive development and viability, this individual member of the Pumilio gene family in mice is also not essential for reproduction or viability.

The Puf RNA-binding proteins FBF-1 and FBF-2 inhibit the expression of synaptonemal complex proteins in germline stem cells

“…One intriguing possibility is that mRNAs activated by DAZL and CPEB are silenced in immature germ cells by FBF-like repressors. Consistent with this possibility, the mammalian FBF homolog PUM2 is expressed in undifferentiated germ cells and has been reported to interact with DAZL (Moore et al, 2003;Xu et al, 2007). It will be interesting to investigate whether mouse meiotic mRNAs are transcribed in immature germ cells but kept silenced by PUM2/FBF, as we have shown here for C. elegans.…”

The DAZL and PABP families: RNA-binding proteins with interrelated roles in translational control in oocytes

“…The PUF family protein PUM2 is expressed in human, mouse and X. laevis oocytes and is also highly expressed in human and mouse PGCs, gonocytes and spermatagonia and at lower levels in primary and secondary spermatocytes (Moore et al 2003, Xu et al 2007). xPUM2 acts as a translational repressor via binding to PBEs (see sequences required for cytoplasmic polyadenylation), and also contributes to regulated cytoplasmic polyadenylation (Table 3) (Nakahata et al 2001(Nakahata et al , 2003.…”

“…Genetic evidence for a physiologically important role in mammalian oogenesis is absent since Pum2 null mice are fertile. However, male mice do display a significant reduction in testis size (Xu et al 2007) and the lack of ovarian phenotype could be due to a level of redundancy with mouse PUM1. Thus, further work is required to clarify the functional and physiological consequences of DAZL-PUM2 interactions.…”

FBF and Its Dual Control of gld-1 Expression in the Caenorhabditis elegans Germline

“…In Drosophila and Caenorhabditis elegans, both Pumilio and FBF are required for maintenance of germline stem cells (Lin and Spradling 1997;Forbes and Lehmann 1998;Crittenden et al 2002), and PUF proteins have been implicated in stem cell controls in other organisms, including humans Salvetti et al 2005;Xu et al 2007). In addition, PUF proteins influence embryonic patterning (Barker et al 1992), germline sex determination (Zhang et al 1997), and memory formation (Dubnau et al 2003).…”