Fig. 1.

Vulval development in C. elegans. a) A cartoon of a C. elegans hermaphrodite in the third larval (L3) stage, illustrating the relative position of VPCs and some adjacent mesodermal cells: somatic gonad (including the AC) and (ventral) body wall muscle. VPC lineages in wild type (let-60(+)) (b) and a representative animal with an activated Ras genotype (let-60(n1046gf)) (c). Normally, through coordination of several cell signals, 3 of 6 VPCs are “induced” to divide and produce cells of the vulva. In most let-60(n1046gf) animals, more than 3 (and up to 6) VPCs divide to produce vulval cells. Mid-body region of fourth larval stage (L4) hermaphrodites, identifying the vulval structures produced from VPC descendants in let-60(+) (d) and let-60(n1046gf) (e) animals. A single vulval structure forms from the offspring of 3 induced VPCs (white arrow), and additional structures result if ectopic VPCs divide to produce vulval cells (black arrow).