The many roads to C. elegans dauer arrest: A review and perspective

The Caenorhabditis elegans dauer stage is an alternative developmental stage to the third larval stage of the nematode. The decision to enter the dauer stage instead of continuing development into reproductive adults is triggered during the late larval stage 1 (L1)/early larval stage 2 (L2) by environmental stressors such as starvation, crowding, or extreme temperatures. Several regulatory pathways can trigger the dauer decision. These pathways, which include the insulin signaling pathway (ILS), the TGF-ꞵ pathway, and the more recently discovered cytokine interleukin ILC-17.1 pathway, appear to act as independent and parallel inputs into the C.elegans developmental program. In this review, we discuss these regulatory pathways and their possible interactions, with a focus on the lesser-studied ILC-17.1 pathway. We then briefly discuss the intriguing possibility that the many routes into dauer can drive differences in gene expression in dauer larvae, which, if they persist, could allow dauers to survive in and exploit different niches upon their exit from the dauer state.