Under specific circumstances, skin cells can change their differentiated state from a skin to a neuronal state. This is observed in several systems, from worms to flies to vertebrates. For example, in the L2 stage of C. elegans, the differentiated skin cell V5 generates a neuroblast that then forms two mechanoreceptor neurons, PVD and PDE. Emmons and co-workers previously described that a loss of the conserved bHLH transcription factor lin- 32 (Atoh1 in mouse) results in a failure of this skin-to-neuron transformation (Zhao, et al., 1995); instead, the neuroblast converts into a skin cell, like all other V cells do. Using forward genetic screens, we have identified additional genes required in this skin-to-neuron transformation. Our mutant collection contains a subset of conserved transcription factors that may have similar roles in vertebrates. As proof of principle, we have isolated several lin-32 alleles: one of which is a regulatory mutation in a region that is completely conserved between 5 species of nematode and contains a C2H2-type zinc finger binding site. In another mutant, dopy-1, lin-32::gfp expression fails to be induced in the V5 lineage, suggesting that we isolated a regulator of lin-32 expression. dopy-1 is a C2H2 zinc finger transcription factor and while it may control lin-32 directly, it is broadly expressed, suggesting that other activators of lin-32 remain to be identified. Another gene we have implicated in the skin-to-neuron transition is hlh-2, a gene encoding a highly conserved protein known to heterodimerize with LIN-32 and play a role in male ray neurogenesis (Portman, et al., 2000). The allele of hlh-2 that we retrieved also appears to be a regulatory allele that deletes upstream promoter elements. Using a parallel candidate gene approach, we identified vab-15 as another mutant where the skin-to-neuron transformation fails to occur. vab-15 was previously found to encode the C. elegans homolog of the vertebrate Msx homeobox genes (Du, et al., 2001). We find that vab-15 also controls lin-32 expression. From a collection of over 30 mutant alleles in which neurons in the postdeirid lineage fail to be induced, we expect to find more genes that act to induce lin-32 expression and/or cooperate with lin-32 to control induction of the postdeirid lineage. We will present our analysis of these additional mutant loci.

Affiliations:
- Hubrecht Institute, Utrecht, The Netherlands
- Department of Biochemistry & Biophysics, Columbia University, New York City, NY.