The GLP-1/Notch transmembrane receptor is required for mitotic proliferation of germline stem cells (GSCs) and for early embryonic development in C. elegans. We identified
hsp-90(
om40), in a screen for genetic enhancers of a
glp-1 temperature sensitive allele,
glp-1(
bn18ts), which reduces but does not eliminate GLP-1/Notch signaling.
hsp-90 encodes the C. elegans ortholog of the molecular chaperone HSP90, thus the discovery of this
hsp-90-
glp-1 interaction reveals an important role for HSP90 in GLP-1/Notch signaling and germline development in C. elegans.
hsp-90 had previously been shown to be an essential gene in C. elegans that produces a variety of phenotypes when mutated or knocked down by RNAi including sterility, embryonic and larval lethality, constitutive dauer formation, defective motility, and various germline defects. Proper HSP90 function requires the activity of numerous co-chaperones; at least two dozen co-chaperones are known in various organisms and C. elegans has orthologs of 17 of them. We are examining which, if any, of these co-chaperones play a role in GLP-1/Notch signaling in C. elegans. We are using RNAi by feeding to systematically knock down the expression of all known C. elegans co-chaperone orthologs in wildtype and the sensitized
glp-1(
bn18ts) background. In the initial stage of this project, we are examining the effects on brood size and embryonic/early larval viability. To date, we have knocked down 13 co-chaperones. Preliminary results uncovered interactions between
glp-1(
bn18) and seven co-chaperone genes:
sti-1,
hip-1,
pph-5,
daf-41, D1054.3,
ttc-1,
ttc-4. The observed effects include, depending on the gene, reduced brood size, sterility, embryonic lethality, and a variety of larval defects including lethality. These data suggest roles for the HSP90 co-chaperone machinery in promoting GLP-1/Notch signaling during germline and embryonic development.
lin-12, a gene paralogous to
glp-1 and orthologous to Notch, functions redundantly with
glp-1 during late embryogenesis in C. elegans. Therefore, it is possible that the embryonic and early larval effects of co-chaperone knockdown result from reduced activity of both GLP-1 and LIN-12.