In humans, defects in glycopeptide hormone signaling can lead to a spectrum of health problems including infertility, metabolic imbalances, and developmental defects. Ligands for these receptors include the gonadotropins, FSH and LH, and the thyroid regulator TSH. In C. elegans, the G-protein coupled receptor FSHR-1 (follicle-stimulating hormone receptor) is the sole ancestral ortholog of the human receptors for FSH, LH and TSH. Neverthelss, putative
fshr-1 null deletion mutants display no obvious plate or DIC phenotypes, although
fshr-1 has recently been shown to play a role in synaptic structure (Sieburth et al., 2005). To identify additional biological functions for FSHR-1 and to discover genes and pathways that act coordinately with FSHR-1, we have carried out a genome-wide RNAi screen in the
fshr-1 mutant background.
Completion of this screen, including the verification of all postive clones, has identified 114 genes that produce a pronounced phenotype in the
fshr-1 null background but not in wild-type. The specificity of these interactions was confirmed by several approaches including the use of a GFP-tagged rescuing construct for
fshr-1 that abrogates the mutant phenotypes. The observed synthetic phenotypes can be placed into three general categories: (1) embryonic and larval lethality, (2) fertility defects, and (3) growth retardation. Of the 114 genes identified, 29 (26%) are predicted to function in signal transduction pathways. The remainder includes genes involved in transcription, translation, protein degradation, metabolism, glycosylation, cell architecture, and intracellular transport, as well as many novel proteins. The identities of these genes as well as descriptions of the mutant phenotypes they produce in conjunction with
fshr-1 will be presented along with FSHR-1 expression studies.
Interestingly, one of the RNAi clones uncovered by our screen targets the
fbf-1 and
fbf-2 paralogs. Specifically,
fshr-1 dramatically enhances the Mog phenotype induced by the simultaneous partial depletion of both fbfs. Furthermore,
fshr-1 variably (but reproducibly) enhances the Glp phenotype of the fbfs under similar conditions. In contrast, loss of
fshr-1 function does not enhance or induce a Mog or Glp phenotype in either
fbf-1 or
fbf-2 single mutants, although
fbf-2;
fshr-1 double mutants display a higher penetrance of the Fem phenotype than do
fbf-2 single mutants. We are currently carrying out epistasis analysis to determine where in the known germline sex determination pathway
fshr-1 may exert its effects in combination with the fbfs.