Intestinal fat is derived from different sources including dietary fatty acids, new (de novo) synthesis and cell compartments called lysosomes (LYS). In wildtype hermaphrodite worms (left), lipids are packaged into yolk particles (YP), which are then secreted into a cavity called the pseudocoelom and taken up by egg cells (oocytes) in the germ line. The signals that promote yolk production have not yet been identified, but are likely to come from cells in the somatic gonad (dotted arrow). In the glp-1 mutants (right), the stem cells that give rise to the egg cells are absent: however, these sterile worms still produce yolk particles, which accumulate in the body and trigger a stress response. This response involves lipase enzymes (not shown) within the lysosomes that produce metabolites of oleic acid (OA). These molecules act as signaling molecules to activate, either directly or indirectly, the transcription factors NHR-80 and SKN-1, which promote longevity. One of the roles of SKN-1 is to limit the accumulation of fat and yolk.