19 Development of the Vulva

Abstract

I. INTRODUCTION AND OVERVIEW
Formation of the hermaphrodite vulva has been particularly amenable to genetic and developmental studies. These studies have revealed that vulva formation is a microcosm of events important in the development of all animals and that these events utilize molecules that appear to be conserved in all animals. Indeed, some of these molecules or their involvement in development were first identified through studies of vulval development in Caenorhabditis elegans.

The vulva consists of 22 cells and serves as the passageway through which sperm enter and fertilized eggs leave the gonad (Fig. 1). Vulval development may be roughly divided into four stages. First, in the L1 stage, the vulval precursor cells (VPCs) are born. The VPCs are six hypodermal cells, consecutively numbered P3.p through P8.p, each of which has the potential to contribute cells to the vulva. Second, in the early L3 stage, cell-cell interactions specify the fates of the VPCs. In wild-type hermaphrodites, three discrete signaling events specify P5.p, P6.p, and P7.p to adopt vulval fates (i.e., to undergo lineages that result in the production of vulval cells) and P3.p, P4.p, and P8.p to adopt a non-vulval fate (i.e., to produce additional hypodermal cells). Third, the VPCs execute the fates that have been specified, generating the appropriate number and types of vulval cells. Fourth, the vulval cells undergo cell movements, cell fusion, and eversion to form the mature vulva.

The somatic gonad influences vulval development. The most pervasive influence is provided by the anchor cell (AC), which...