gon-2 encodes a TRPM family cation channel that is required for the initiation of postembryonic divisions by the gonadal precursor cells. Our working hypothesis is that GON-2 protein is expressed in the somatic gonadal cells and mediates the uptake of cations such as calcium and magnesium that are required for cell cycle progression. To begin to test this hypothesis, we generated rabbit polyclonal antibodies against a peptide corresponding to part of the C-terminal cytoplasmic region of GON-2. Based on western blots with these antibodies, we find that GON-2 is expressed in multiple tissues, including the adult gonad and intestine. Through mosaic analysis we found that
gon-2 activity is required within the MS lineage, but not the E lineage, in order for gonad development to proceed normally. This suggests that
gon-2 function within the somatic gonad, but not the intestine, is likely to be required for gonad development. Hypomorphic mutations in
gon-2 cause a maternal effect gonadless phenotype, but strong loss-of-function alleles cause zygotic sterility. These animals produce both sperm and oocytes, but very few fertilized eggs. Fertility cannot be rescued by mating with wild type males, suggesting that the oocytes may be refractory to fertilization or the ovulation program may be defective. We are examining the ovulation program of the zygotic sterile animals and testing the ability of an
ipp-5 mutation that suppresses the ovulation defect of
let-23(lf) to rescue sterility caused by
gon-2(lf) . We conducted a large scale reversion screen using
gon-2(
q388ts) in order to search for intragenic and extragenic suppressor mutations. We identified four loci that can mutate to suppress
gon-2(
q388) ,
gem-1-4 ( g on-2 e xtragenic m odifier). Gain-of-function mutations in
gem-1 are capable of suppressing
gon-2(0) . Since
gem-1 encodes a multi-pass transmembrane protein, we suspect that GEM-1(gf) may bypass the requirement for GON-2 by providing an alternative pathway for cation uptake. We also identified six potential intragenic revertants of
gon-2(
q388) . We are examining the sequence of
gon-2 from these mutants in order to determine whether they suggest an interaction between the
q388 -containing region and another portion of the protein.