Vulval morphogenesis in C. elegans hermaphrodite provides a good system to identify and study the role of genes regulating epithelial invagination and cell shape changes. During L4 stage, 22 vulval progeny differentiate to give rise to seven different cell types (vulA to vulF). This process involves cell movements, cell-shape changes and cell fusions. Among the genes regulating these processes, the LIM homeobox family member
lin-11 plays a major role. Mutations in
lin-11 were initially isolated based on their egg-laying defective phenotype. This phenotype results from differentiation defects in the vulva and vulval-uterine connection. To understand the regulation of
lin-11 during development, we have dissected its regulatory region and identified tissue-specific elements that direct
lin-11 expression in vulval cells and uterine pi lineage cells. The vulval-specific enhancer responds to LIN-17 Frizzled mediated Wnt signaling during early stages of vulval development. This expression leads to the wild-type vulval invagination. Currently, we are analyzing the role of known Wnt pathway components in mediating
lin-11 vulval expression. To study the precise function of
lin-11 in vulval cells, we have examined its spatiotemporal expression using different
lin-11::GFP transgenic strains. We find that
lin-11 is expressed in a dynamic manner in both 1o and 2o lineage cells. Thus,
lin-11 is likely to play multiple roles in vulval cells. This is also supported by the
ajm-1::GFP cell junction marker expression that reveals cell boundaries. In contrast to wild-type, where vulval cells selectively fuse to form seven concentric rings, each corresponding to one vulval cell type,
lin-11 mutant vulval cells show extensive defects in cell fusion events. To further study the fate of vulval cells in
lin-11 mutants, we have analyzed the expression of various vulval markers and show that mutant vulval cells fail to express any of the markers suggesting defects in cell fate specification. To study the effect of altered pattern of
lin-11 expression in vulval cells, we have carried out two additional experiments. First, we examined the effect of
lin-11 overexpression using a heat shock promoter. Heat shocks given during early stages (Pn.px and Pn.pxx cells) caused excessive vulval invagination suggesting that precise regulation of
lin-11 is necessary for the wild-type invagination. Second, using a conditional RNAi approach we have shown that removal of LIN-11 activity during terminal differentiation results in abnormal vulval morphology. Thus, temporal expression of
lin-11 plays a critical role during vulval morphogenesis.