THE TERMINAL DIFFERENTIATION FACTOR LIN-29 IS REQUIRED FOR PROPER VULVAR MORPHOGENESIS AND EGG-LAYING IN CAENORHABDITIS-ELEGANS

Caenorhabditis elegans vulval development culminates during exit from the L4-to-adult molt with the formation of an opening through the adul t hypodermis and cuticle that is used for egg laying and mating, Vulva formation requires the heterochronic gene lin-29, which triggers hypo dermal cell terminal differentiation during the final molt. lin-29 mut ants are unable to lay eggs or mate because no vulval opening forms; i nstead, a protrusion forms at the site of the vulva, We demonstrate th rough analysis of genetic mosaics that lin-29 is absolutely required i n a small subset of lateral hypodermal seam cells, adjacent to the vul va, for wild-type vulva formation and egg laying. However, lin-29 func tion is not strictly limited to the lateral hypodermis. First, LIN-29 accumulates in many non-hypodermal cells with known roles in vulva for mation or egg laying, Second, animals homozygous for one lin-29 allele , ga94, have the vulval defect and cannot lay eggs, despite having a t erminally differentiated adult lateral hypodermis, Finally, vulval mor phogenesis and egg laying requires lin-29 activity within the EMS line age, a lineage that does not generate hypodermal cells.