A branched-chain fatty acid is involved in post-embryonic growth control in parallel to the insulin receptor pathway and its biosynthesis is feedback-regulated in C-elegans

Growth and development of multicellular organisms are controlled by signaling systems that sense nutrition availability and metabolic status. We report a novel and surprising factor in Caenorhabditis elegans development, the monomethyl branched-chain fatty acid C17ISO, a product of leucine catabolism. We show here that C17ISO is an essential constituent in a novel mechanism that acts in parallel with the food-sensing DAF-2 (insulin receptor)/DAF-16 (FOXO) signaling pathway to promote post-embryonic development, and that the two pathways converge on a common target repressing cell cycle. We show that C17ISO homeostasis is regulated by a SREBP-1c-mediated feedback mechanism that is different from the SREBP-1c-mediated regulation of common fatty acid biosynthesis, as well as by peptide uptake and transport. Our data suggest that C17ISO may act as a chemical/nutritional factor in a mechanism that regulates post-embryonic development in response to the metabolic state of the organism.