In the nematode C. elegans, the vulva forms from agroup of six vulval precursor cells (VPCs). These cells give riseto the three vulval lineages: 1º (central vulva), 2º (lateralvulva), and 3º (hypodermis). Experiments have determined that thesecells constitute an “equivalence group”, meaning that they are eachcapable of forming all three vulval lineages. The crucial factor intheir fate decision turns out to be their proximity to the anchorcell, which is a cell located in the central region of the gonad ofthe developing worm:
These experiments suggest that some signal produced by theanchor cell is required to specify vulval fates. You have decidedto carry out a study to identify the molecular basis for thissignal. You begin by performing a genetic screen for mutants thatlack a vulva (“vulvaless” mutants). One of the mutations youidentify in this screen affects a gene called lin-3, whichencodes a secreted protein related to the epidermal growth factor(EGF) family.
Propose a hypothesis about the possible role oflin-3 in vulval specification in the C. elegansembryo.
