A SCREEN FOR GENETIC-LOCI REQUIRED FOR HYPODERMAL CELL AND GLIAL-LIKECELL-DEVELOPMENT DURING CAENORHABDITIS-ELEGANS EMBRYOGENESIS

The Caenorhabditis elegans lin-26 gene is expressed in all nonneuronal ectodermal cells. To identify genes required to specify the fates of ectodermal cells, we have conducted screens designed to identify loci whose zygotic function would be required for normal lin-26 expression. First, we examined 90 deficiencies covering 75% of the genome; second , we examined the progeny of 3600 genomes after EMS mutagenesis. We id entified six loci that appear to be required for normal lin-26 express ion. We argue that the deficiency eDf19 deletes a gene involved in spe cifying hypodermal cell fates. The genes emb-29 (previously known) and ale-1 (newly found) could be involved in a cell cycle function and/or in specifying the fates of some precursors within different lineages that generate hypodermal cells and nonectodermal cells. We argue that the overlapping deficiencies qDf7, qDf8 and qDf9 delete a gene require d to limit the number of nonneuronal ectodermal cells. We suggest that the deficiencies ozDf2, itDf2 and nDf42 delete genes required, direct ly or indirectly, to repress lin-2G expression in cells that normally do not express lin-26. We discuss the implications of these findings c oncerning the generation of the ectoderm.