A hypothesis for the tissue specificity of nematode parasites.

Recent work from Riddle and coworkers has shown that in the free-living soil nematode, Caenorhabditis elegans, the decision to become a developmentally arrested, dispersal form known as the dauer ("enduring") larva is controlled, at least in part, by transcription of a wild-type allele at the daf-7 locus. daf-7 mutants are "constitutive dauers." Using this model as a general paradigm for nematode development, I propose that many nematode parasites behave as though they were daf-7 mutants. This will ensure developmental arrest at the L3 stage. I further propose that these organisms obtain the daf-7 gene product required for reentry into the developmental pathway from the mammalian host and that their tissue localization is dictated by the daf-7 homologue that is uniquely recognized by the cognate receptor.