The distal end of the germline consists of a population of proliferative germ cells that switch from proliferation to meiotic development as they move proximally. The GLP-1/Notch signaling pathway regulates this switch. Previous work has shown that
gld-1 is also involved in regulating meiotic entry based on
gld-1(0) partial suppression of
glp-1(0) premature entry into meiosis phenotype, as well as the excess proliferation (germline tumor) that occurs in the
gld-2(0)
gld-1(0) double mutant. Genetic epistasis places
gld-1 and
gld-2 downstream of GLP-1/Notch signaling. We are interested in identifying additional genes involved in regulating the entry into meiosis decision, as well as determining the regulatory relationships between known and newly identified factors. GLD-1 protein levels are very low at the most distal end and increase proximally until reaching maximum levels approximately 20 cell diameters from the distal end, which is the approximate location where cells first show evidence of meiotic entry. We show that the GLP-1/Notch signaling pathway is responsible for repressing GLD-1 accumulation as GLD-1 levels are increased when signaling is eliminated. This regulation is likely not transcriptional as
gld-1 RNA in situs show roughly equivalent levels in
glp-1(+) and
glp-1(-) animals. We further show that ectopically increasing GLD-1 accumulation in the distal end causes germ cells to enter meiosis earlier. These data suggest that a major mechanism by which the GLP-1/Notch signaling pathway controls the proliferation versus meiotic development decision is by regulating the spatial pattern of GLD-1 accumulation. In an attempt to identify other factors necessary for control of meiotic entry, we conducted genetic screens and identified mutations in the
nos-3 gene, which is homologous to Drosophila Nanos. Interestingly, FBF-1 and FBF-2, two nearly identical proteins that are homologous to Drosophila Pumilio, have also been implicated in regulation of meiotic entry by inhibiting distal GLD-1 accumulation. We show that
nos-3 also affects GLD-1 accumulation, however unlike FBF,
nos-3 promotes GLD-1 accumulation, a function that is redundant with
gld-2. In a
gld-2;
nos-3 double mutant, GLD-1 accumulation is markedly reduced. Furthermore,
nos-3 suppresses the premature entry into meiosis and high distal GLD-1 accumulation phenotypes of
fbf-1 fbf-2 mutants. One model to explain these results is the GLP-1/Notch signaling represses the activities of GLD-2 and NOS-3 in the distal end to keep GLD-1 accumulation low and allow for the stem cell population to be maintained.