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 groupâ€, 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.
