ABSTRACT: BACKGROUND: In the nematode, Caenorhabditis elegans, a conserved insulin-like signaling pathway controls larval development, stress resistance and adult lifespan. AGE-1, a homolog of the
p110 catalytic subunit of phosphoinositide 3-kinase (PI3K), comprises the major effector pathway downstream of the insulin receptor, DAF-2. Phospholipid products of AGE-1/PI3K activate AKT/PKB kinase signaling via PDK-1. AKT/PKB signaling antagonizes nuclear translocation of the DAF-16/ FOXO transcription factor. Reduced AGE-1/PI3K signaling permits DAF-16 to direct dauer larval arrest and promote long lifespan in adult animals. In order to study the downstream effectors of AGE-1/PI3K signaling in C. elegans, we conducted a genetic screen for mutations that suppress the constitutive dauer arrest phenotype of
age-1(
mg109) animals. RESULTS: This report describes mutations recovered in a screen for suppressors of the constitutive dauer arrest (daf-C) phenotype of
age-1(
mg109). Two mutations corresponded to alleles of
daf-16. Two mutations were gain-of-function mutations in the genes,
akt-1 and
pdk-1, encoding phosphoinositide-dependent serine/threonine kinases. A fifth mutation,
mg227, located on chromosome X, did not correspond to any known dauer genes, suggesting that
mg227 may represent a new component of the insulin pathway. Genetic epistasis analysis by RNAi showed that reproductive development in
age-1(
mg109);
akt-1(
mg247) animals was dependent on the presence of
pdk-1. Similarly, reproductive development in
age-1(
mg109);
pdk-1(
mg261) animals was dependent on
akt-1. However, reproductive development in
age-1(
mg109);
mg227 animals required only
akt-1, and
pdk-1 activity was dispensable in this background. Interestingly, while
mg227 suppressed dauer arrest in
age-1(
mg109) animals, it enhanced the long lifespan phenotype. In contrast,
akt-1(
mg247) and
pdk-1(
mg261) did not affect lifespan or stress resistance, while both
daf-16 alleles fully suppressed these phenotypes. CONCLUSIONS: An
age-1(
mg109) suppressor screen identified activating mutations in two known pathway components which provided insights into their regulation. In particular, the interdependence of
akt-1 and
pdk-1, even in activated forms, supports the existence of AGE-1-independent pathways for these phospholipid-dependent kinases. Phenotypic analysis of these alleles shows that the larval and adult outputs of AGE-1/PI3K are fully separable in these mutants.