The interaction between GLP-1 signaling and the GLD-1 and GLD-2 pathways is important in regulating the switch from mitotic proliferation to meiosis in the germ line. The GLD-1 and GLD-2 pathways function redundantly to promote meiosis and/or inhibit mitosis. In the distal germ line, GLP-1 signaling ultimately inhibits the activities of GLD-1 and GLD-2 pathways to promote proliferation. We found that
atx-2(RNAi) causes a proliferation defect in wild type animals, enhances a weak allele of
glp-1 , and suppresses the
gld-2 gld-1 meiotic entry defect. Thus,
atx-2 activity promotes germline proliferation and represses meiosis. We also find that
atx-2(RNAi) causes a Mog ( m asculinization o f the g erm line) defect and suppresses
fog-2 , indicating that
atx-2 promotes the spermatogenesis to oogenesis switch. It has previously been shown that
atx-2 is required for early embryogenesis (Gonczy et al. 2000; Kiehl. et al. 2000; Kamath et al. 2003). Our data suggest that ATX-2 is not a positive regulator of the GLP-1 pathway, neither is GLP-1 the sole positive regulator of ATX-2. Our current hypothesis is that
atx-2 functions in parallel with
glp-1 , and represses meiosis by working in opposition to the GLD-1 and GLD-2 pathways. In addition, it acts downsteam of
fog-2 to promote the female germ cell fate. Based on analysis of mammalian ataxin-2, we hypothesize that ATX-2 regulates target genes at a post-transcriptional level to promote proliferation and the oocyte fate. Our experiments to date were done using
atx-2(RNAi). Due to the limitations of RNAi, we are screening for
atx-2 mutations. Using either UV or EMS as a mutagen, we are screening for suppressors of
fog-2 that are linked to a marker near
atx-2 . We are also collaborating with the Conradt Lab (Dartmouth College) to recover a deletion allele. ATX-2 is a 959 amino acid protein that is related to mammalian ataxin-2. Ataxin-2-like proteins are found in mammals, insects and plants and contain two conserved regions, named the ATX2-N and ATX2-C domains (Satterfield et al. 2002). The ATX2-N domain is related to a portion of S. cerevisae PBP1 ( P rotein that B inds P oly(A)-binding Protein), while the ATX2-C domain is essentially a PAM2 ( P oly( A )-Binding Protein, Cytoplasmic 1 Interacting M otif 2) sequence. Mammalian ataxin-2 has been reported to bind A2BP ( A taxin- 2 B inding P rotein), which is itself an RNA-binding protein (Pulst et al. 2000). We find that
atx-2 interacts phenotypically with two C. elegans A2BP-related genes,
fox-1 and
spn-4 . Therefore, we are now using a directed yeast two-hybrid approach to test whether FOX-1 and SPN-4 can physically interact with ATX-2. We hypothesize that these interactions may be important for regulating specific target mRNAs. Another likely interaction partner is PAB-1 ( P oly( A )- B inding P rotein), which we predict would bind to the ATX-2 PAM2 motif.
pab-1(RNAi) produces a severe germline proliferation defect. Given these results, we are also testing whether PAB-1 binds to ATX-2 in our assay. Gonczy P et al. (2000) Nature 408, 331-336 Kiehl TR et al. (2001) J MOL Neuroscience 15, 231-241. Kamath RS et al. (2003) Nature 421, 231-237. Satterfield TF et al. (2002) Genetics 162, 1687-1702. Pulst SM et al. (2000) Hum Mol Genet 9(9), 1303-1313.