A novel WD40 protein, CHE-2, acts cell autonomously in the formation of C-elegans sensory cilia

To elucidate the mechanism of sensory cilium formation, we analyzed mutants in the Caenorhabditis elegans che-2 gene. These mutants have extremely sho rt cilia with rm abnormal posterior projection, and show defects :in behavi ors that are mediated by ciliated sensory neurons. The che-2 gene encodes a new member of the WD40 protein family, suggesting that it acts in protein- protein interaction. Analysis of mutation sites showed that both the aminot erminal WD40 repeats and the carboxyl-terminal non-WD40 domain are necessar y for the CHE-2 function. CHE-2-tagged green fluorescent protein is localiz ed at the cilia of almost all the ciliated sensory neurons. Expression of c he-2 in a subset of sensory neurons of a che-2 mutant by using a heterologo us promoter resulted in restoration of the functions and cilium morphology of only the che-2-expressing neurons. Thus, che-2 acts cell-autonomously. T his technique can be used in the future for determining the function of eac h type of che-2-expressing sensory neuron. Using green fluorescent protein, we found that the extension of cilia in wild-type animals took place at th e late embryonic stage, whereas the cilia of che-2 mutant animals remained always short during development. Hence, the abnormal posterior projection i s due to the inability of cilia to extend, rather than degeneration of cili a once correctly formed. Expression of che-2 in a che-2 mutant under a heat shock promoter showed that the extension of cilia, surprisingly, can occur even at the adult stage, and that such cilia can function apparently norma lly in behavior.