Germ cell sex determination in Caenorhabditis nematodes is regulated by a network of translational repressors [1]. In species where the XX female has evolved self-fertility, this network is reconfigured to allow limited spermatogenesis. This is achieved by changes to both properties of repressor proteins and in the cis-regulatory sites of their client mRNAs [e.g. 2]. Here, we focus on a highly conserved mRNA-binding protein, GLD-1, and its C. elegans-specific cofactor, FOG-2. Previous work has implicated both proteins in the translational regulation of C. elegans tra-2, a key promoter of female fate [3-5]. The STAR family protein GLD-1 targets hundreds of mRNAs in addition to tra-2 [6]. Consistent with this, GLD-1 is not only required for XX spermatogenesis, but for other aspects of meiosis and oocyte differentiation. These oocyte-related roles are conserved across the Caenorhabditis genus. In contrast to this pleiotropy, the function of FOG-2 is restricted to specification of XX spermatogenesis [7]. fog-2 is the product of a recent gene duplication, and is found only in C. elegans, consistent with it representing an essential player in the emergence of the novel self-fertile phenotype [8,9]. We seek to understand the molecular mechanism of how FOG-2 affects sex determination, and in particular how it modifies the activity of GLD-1 and/or its target mRNAs. We used CRISPR/Cas9 to introduce small epitope tags into the endogenous TRA-2 and FOG-2 proteins, and are currently using these to examine expression in wild-type and mutant contexts. We are also working to identify proteins that bind to FOG-2, and to compare mRNAs associated with FOG-2 to those already known for GLD-1.
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