Isolation and characterization of mutations causing abnormal eversion of the vulva in Caenorhabditis elegans.

In Caenorhabditis elegans hermaphrodites, morphogenesis of the vulva culminates in a process called vulval eversion, whereby a passageway is made from the uterus through the vulva to the outside of the animal. We have screened for mutations causing abnormal eversion of the vulva (evl mutations) to identify new genes involved in vulval development, and found that evl mutants are relatively common after EMS mutagenesis. We also hoped to identify genes involved in lin-12-mediated cell fate decisions, since lin-12 null mutants have abnormally everted vulvae, but none of the 68 evl mutations recovered in our screen appeared to be good candidates for genes that function with lin-12. Initial genetic and phenotypic analysis of 30 evl mutations revealed that all affect the development of the uterus, but only some affect the vulval precursor cell lineages. We used laser ablation to show that the uterus and anchor cell are important for correct vulval eversion in wild type; the anchor cell is important early in the L3 stage, before the vulval cells have been generated, but not later, when vulval eversion occurs. We conclude that certain evl mutations may influence vulval eversion by primarily affecting the development of the somatic gonad, while others may affect processes required in the development of both structures.