The regulation of the decision between proliferation and differentiation in the C. elegans germline has been well characterized. Central to this inductive cell signaling pathway is the
glp-1 (germline proliferation defective) gene, which codes for a Notch-type receptor protein. GLP-1 receives a signal (LAG-2) from a pair of somatic cells called the distal tip cells (DTC). If the DTCs are killed, or if GLP-1 is not functioning, all the germ cells enter meiosis, leaving no proliferating cells.
ego-3 was isolated from a screen for genetic enhancers of
glp-1. Mutants of
ego-3 are characterized by an early germline defect; in L3 and L4 larvae, the germ cells arrest either in mitosis or early meiosis, their cell cycle state being difficult to interpret. The later germline phenotype is more variable and includes proximal proliferation and defects in oogenesis. Previous three-factor mapping places
ego-3 between
daf-21 and
sdc-3, just to the left of
unc-61. Through SNP (single nucleotide polymorphism) mapping, we have now localized
ego-3 to a region of approximately 118 kb, predicted to include 23 genes. SNP mapping is being continued, while cDNAs of predicted genes in this area are also beginning to be tested by RNA interference.