The insulin/IGF-I receptor-like protein, DAF-2, and the PI3K
p110 catalytic subunit AGE-1, regulate development, fertility and lifespan in C. elegans. The major downstream target of DAF-2/insulin receptor signaling is the FOXO transcription factor, DAF-16. DAF-2 and AGE-1 negatively regulate DAF-16 by preventing its translocation to the nucleus. In the absence of DAF-2/insulin receptor signaling, DAF-16 promotes increased expression of stress response genes and reduced expression of metabolically costly genes, resulting in lifespan extension. This suggests that organisms can control the allocation of metabolic resources to influence longevity. One group of genes reported to be down-regulated in long lived
daf-2 mutants are the vitellogenin (vit) genes, which encode yolk proteins that transport lipids into developing oocytes. To investigate the molecular pathways required for resource allocation to reproduction, we assessed vit expression levels after mating with wildtype males and in sterile mutants. We found that introduction of sperm to
fem-1 mutants that lack sperm rescues fertility and induces vit expression, while introduction of sperm to
daf-2 mutants induces vit expression without affecting fertility. In
fem-3, a mutant that only makes sperm, and in
spe-11, a sperm mutant that affects embryonic divisions after fertilization, vit expression levels were comparable to WT. However, in
spe-9, a fertilization defective sperm mutant, vit expression remained low throughout adulthood. These results suggest that sperm induces vit expression in the intestine of adult hermaphrodites in a
spe-9 dependent manner. This induction is not dependent on gamete production, presence of oocytes, or the early embryogenesis factor,
spe-11. We propose that in long lived
daf-2 mutants DAF-16 acts to inhibit germline functions, which subsequently affects sperm, and specifically
spe-9, leading to vit repression. These findings provide new insight about mechanisms that regulate the balance between resource allocation to reproduction and longevity.