Under conditions of starvation and extreme crowding C. elegans enters the dauer larva, a duration stage alternative to the third larval stage. Dauer larva exhibit a unique morphology, an extended life span and are resistant to many environmental stresses. The decision to form dauer larva is controlled by TGF-beta and insulin signaling pathways, which are defined by a large number of daf mutants and well characterized. However, the subsequent genetic control and the molecular nature of the dramatic morphological changes characterizing dauer larva formation is largely unknown. We used systematic RNA interference (1) ( Julie Ahringer's Chromosome 1 RNAi library and further additional clones) in two different daf-c background strains (
daf-2(
m41) and
daf-1(
m40)) to identify genes specifically required for the dauer molt, dauer morphogenesis, or dauer recovery. Two genes were identified, which are essential for the survival of the dauer molt, a phenotype observed here for the first time. These are the patched related ligand
ptr-23 and the G- protein coupled chemorezeptor
srh-49, which both are potentially involved in signaling events. Both depletion experiments do not cause phenotypes in daf-c backgrounds at the permissive temperature or in the wild type at 25C. Morphogenetically incomplete dauer larva developed when the
p66 subunit of the Mi-2 histone deacetylase complex was depleted. The Mi-2 complex has been implicated in chromatin remodeling and transcriptional repression. This suggests that global transcriptional regulation caused by histone deacetylation and chromatin remodeling is important for dauer larva formation. Depletion of the ras related protein
rab-11.2 interfered with the dauer specific shrinkage of the pharynx, whereas depletion of the developmentally regulated actin gene Y71F9AL.16 resulted in dauer larva with a twisted buccal cavity. These and further observations indicate that systematic RNA interference is an efficient and promising tool to identify genes involved in dauer morphogenesis. Interestingly, we also identified genes, which were essential for hermaphrodite fertility when the animal was passed through the dauer stage, but which did not influence hermaphrodite fertility when the animal had developed as a normal L3 larva.