FOG-1 promotes the sperm fate at the expense of oogenesis in both sexes: XO
fog-1 mutants are somatically male but make only oocytes; similarly XX
fog-1 mutants are somatically hermaphrodite but make only oocytes (1). FOG-1 is a divergent Cytoplasmic Polyadenylation Element Binding (CPEB) protein (2, 3). Xenopus CPEB binds CPEB binding elements (CPEs) in the 3'untranslated region (3'UTR) of target mRNAs to regulate translation via polyadenylation or deadenylation depending on associated cofactors. Genetically, FOG-1 acts at the end of the germline sex determination pathway as does another key regulator of sperm fate specification, FOG-3 (4). Our work provides three lines of evidence suggesting that FOG-1 controls the
fog-3 mRNA directly. First, purified recombinant FOG-1 binds the
fog-3 3'UTR in a CPE-dependent manner in vitro. Second, FOG-1 antibodies immunoprecipitate
fog-3 mRNA from L3 hermaphrodite extracts, whereas control IPs do not. Third, the abundance of an epitope-tagged and rescuing FOG-3 protein drops precipitously in
fog-1 mutants, while
fog-3 mRNA is not reduced. We suggest that FOG-1 promotes sperm fate specification by translationally activating
fog-3 expression. Experiments are in progress to test this idea with transgenes carrying either a wild-type
fog-3 3'UTR or a mutant
fog-3 3'UTR that lacks CPEs.
1. Barton MK & Kimble J (1990)
fog-1, a regulatory gene required for specification of spermatogenesis in the germ line of Caenorhabditis elegans. Genetics 125:29-39.
2. Jin S-W, Kimble J, & Ellis RE (2001) Regulation of cell fate in Caenorhabditis elegans by a novel cytoplasmic polyadenylation element binding protein. Dev. Biol. 229(2):537-553.
3. Luitjens C, Gallegos M, Kraemer B, Kimble J, & Wickens M (2000) CPEB proteins control two key steps in spermatogenesis in C. elegans. Genes Dev. 14(20):2596-2609.
4. Ellis RE & Kimble J (1995) The
fog-3 gene and regulation of cell fate in the germ line of Caenorhabditis elegans. Genetics 139:561-577.