In contrast to the "naked" Caenorhabditis dauer larvae (DL), parasitic nematode DL often retain the previous cuticle layer, likely as environmental protection while surviving outside of a host. Pristionchus pacificus, a nematode that is found to associate with beetles, is similarly ensheathed as pharate DL. To examine the genetic and developmental mechanisms that control dauer entry, cuticle formation, and responses to host cues, we characterized two P. pacificus dauer-constitutive mutants,
tu391 and
csu60. Both Daf-c alleles are recessive, temperature-sensitive, and incompletely penetrant, with a subset of the emerging DL exhibiting a transient, stage-specific molting defect wherein the retained J2 cuticle loosens completely to incarcerate the DL. Affected active DL shed this cuticle within 24 hours. Interestingly,
csu60 forms DL only at 20 deg C, but not at 15 deg C or 25 deg C. In addition,
tu391 mutants are found to be dye-filling defective in most stages. The abundance of DL in these Daf-c mutants provided us with an opportunity to investigate if P. pacificus DL and young adults differ in olfactory response to host odors or carbon dioxide, as such valence changes have been observed in response to CO2 in C. elegans. We found that unlike C. elegans, both the mutant DL and adults show repulsion to CO2. Wild-type,
tu391, and
csu60 DL all exhibit strong attraction towards the beetle host pheromone, ZTDO, but wild-type and
tu391 young adults are only mildly attracted to or repelled by ZTDO, respectively, indicating a shift in olfaction preference from DL to adulthood.
csu60 adults, however, exhibit a much stronger attraction to ZTDO, and hence,
csu60 lacks the olfactory valence change typical of the transition between DL and young adults. Using whole genome sequencing and mapping, we found that
tu391 maps to a 27 Mb region of Chromosome I that contains 17 mutations, while
csu60 is one of 11 genes found within a 95 kb deletion on Chromosome II. As a candidate for
tu391, we are investigating UMM-S207-12.31, a patched-related gene homologous to
ptr-4, which is involved in molting regulation in C. elegans. We are also interested in UMM-S10-1.4, a gene located within the
csu60 deletion that is related to C. elegans HydroxySteroid Dehydrogenase (hsd) genes. hsd genes participate in delta4-dafachronic acid (DA) synthesis, which helps prevent dauer formation through the binding of DA to DAF-12 (Patel et al. WBPaper00032624). We are currently conducting transgenic rescue to confirm if these mutations are responsible.