| Vulval development in C. elegans provides a good model system for studying cell-cell interactions that specify distinct cell fates from a group of initially equivalent cells and eventually leads to the correct formation of an organ. Numerous work has been done to elaborate the signaling events during VPC fate specification, but the molecular identity of the lateral signal has been elusive for almost two decades. In this study, I took advantage of the completely sequenced C. elegans genome to carry out a computational approach to identify genes encoding the lateral signal. I demonstrate that among the ten putative dsl genes, lag-2, apx-1 and dsl-1 are functionally redundant components of the lateral signal. Transcription of all three genes is initiated or upregulated in VPCs in response to the inductive signaling; and a conserved "EBSX" motif may play an essential role in their transcriptional regulation. I also show that LIN-1, an Ets protein of the Elk-1 subfamily, is a positive regulator of lateral signal gene expression in the 1° cell. These findings lead us to propose a model of how the components of the inductive signaling, including the EGF-EGFR-Ras-MAPK cascade as well as downstream effectors LIN-1 and SUR-2, act coordinately to ensure the activation of the lateral signal at the right moment and in the right place. |
