We describe the phenotypic analysis and molecular characterization of a C. elegans gene
evl-20 .
evl-20 was identified in a screen for mutants that phenocopy
lin-12 loss-of-function phenotype and produce sterile animals with everted vulva (Seydoux et al., 1993). We have cloned
evl-20 and shown that it encodes a developmentally conserved ARF-like (ARL) protein most closely homologous to human ARL2. ARFs are small guanidine-nucleotide binding proteins that belong to the Ras GTPase superfamily, and our analysis represents the first mutational study of a metazoan member of the ARF gene family. We show that a mutation in
evl-20 results in a highly abnormal vulval lineage. The lineage defects are not caused by misspecification of vulval cell fates since
evl-20 fails to show genetic interactions with the Ras signaling pathway responsible for vulval induction and expression of a vulval differentiation marker,
egl-17::gfp , appears normal in
evl-20 mutant animals.
evl-20 mutants also display underproliferation of somatic gonad and germ line tissues, as well as male tail morphogenesis defects. Results of phenotypic and germ line mosaic analyses combined with data obtained in intestinal cell DNA quantification experiments demonstrate that the underproliferation phenotype of
evl-20 mutants is not caused by DNA replication or karyokinesis defects, but is produced by defective cytokinesis. Germ line mosaic analysis also shows that
evl-20 is not required for germ line proliferation, progression through meiosis, or sperm and oocyte development, and that the germ line defects result from aberrant somatic gonad development. Maternal contribution is necessary for embryogenesis, and elimination of both maternal and zygotic functions of
evl-20 by RNAi disrupts several aspects of embryonic development including proliferation, hypodermal enclosure and elongation. A GFP expression reporter construct driven by
evl-20 promoter is expressed in the affected tissues and in most if not all neurons, which show no detectable phenotype in
evl-20 animals. Using yeast two hybrid system, we also show that EVL-20 ARL interacts with several components of focal adhesions. Based on our data, we propose that
evl-20arl plays a conserved role in cytokinesis and morphogenesis and may function in regulating actin- or microtubule-based cytoskeleton dynamics. Seydoux, G., Savage, C., and Greenwald, I. (1993). Isolation and characterization of mutations causing abnormal eversion of the vulva in Caenorhabditis elegans, Dev Biol 157 , 423-36.