Dauer

Patrick J. Hu
2007 WormBook  
In response to harsh environmental conditions, C. elegans larvae undergo dauer arrest at the second molt. The past decade has yielded many insights into the signaling pathways and the molecular mechanisms that govern this developmental transition. Dauer pheromone, the major physiologic signal promoting dauer arrest, has been purified, identified, and synthesized. The molecular identities of the vast majority of dauer regulatory genes isolated in initial genetic screens are now known.
more » ... ligands for DAF-12, a nuclear receptor that is the final common target of dauer regulatory pathways, have been identified. The discovery of the Hid (high temperature induction of dauer) phenotype and the results of enhancer screens have greatly expanded the repertoire of dauer regulatory genes. Genomic analysis of dauer arrest has highlighted the role of pathway crosstalk in dauer regulation. Nonetheless, critical questions remain about the mechanistic underpinnings of dauer arrest. Conversely, a heat-stable, hydrophilic "food signal" that provides information about food availability inhibits dauer arrest and promotes dauer recovery. The relative amounts of pheromone and food signal, rather than absolute levels, are critical in determining whether an animal undergoes dauer arrest (Golden and Riddle, 1982) . Increased temperature enhances pheromone-induced dauer arrest (Golden and Riddle, 1984a) , and some temperature-sensitive dauer-constitutive mutants are suppressible by an amber nonsense suppressor (Golden and Riddle, 1984b) , suggesting that dauer arrest is intrinsically dependent upon ambient temperature. Dauer morphology Dauer larvae are morphologically distinct from larvae that develop in replete conditions. Dauers are radially constricted and possess a specialized cuticle with alae (Cassada and Russell, 1975) . Their oral orifices are closed by an internal plug , and their pharynxes are constricted (Vowels and Thomas, 1992) and do not pump (Cassada and Russell, 1975) . Dauers are easily distinguishable from L3 larvae under a dissecting microscope. The dauerspecific cuticle and the lack of pharyngeal pumping confer resistance to many environmental insults, including 1% SDS (Cassada and Russell, 1975) . SDS resistance provides a convenient method for isolating dauers and has greatly facilitated the genetic analysis of dauer formation. Dauer metabolism C. elegans undergoes a metabolic shift between L1 and L2 stages; embryos and L1 larvae use the glyoxylate cycle to generate carbohydrates from lipid stores, whereas L2 and later stages shift toward aerobic respiration and exhibit a relative increase in TCA cycle activity. Dauers do not undergo this shift toward aerobic respiration (Wadsworth and Riddle, 1989) . Relative to growing larvae, dauers also appear to be transcriptionally quiescent but have elevated levels of mRNA encoding the heat shock protein Hsp90 (Dalley and Golomb, 1992; Snutch and Baillie, 1983) and elevated superoxide dismutase (Larsen, 1993; Vanfleteren and De Vreese, 1995) and catalase (Vanfleteren and De Vreese, 1995) activities. This suggests that dauers are adapted to resist metabolic stress and is consistent with the observation that they are long-lived (Klass and Hirsh, 1976) .
doi:10.1895/wormbook.1.144.1 pmid:17988074 pmcid:PMC2890228 fatcat:3lbwzbjxifaehegmnerrtqqdvq