lin-3 is required for vulval induction; therefore
lin-3 is either necessary for the generation of the inductive signal by the anchor cell or for the response to the inductive signal by the VPCs.
lin-3 is interesting to us because genetic experiments indicate that
lin-3 acts early in the pathway of vulval induction and because
lin-3 appears to be essential for vulval induction. Other
lin-3 phenotypes include larval lethality, hermaphrodite sterility, and a Mab defect that includes crumpled spicules. The physical location of the
lin-3 locus was identified by transposon tagging as described previously (WBG 11.3). We have defined a region sufficient for rescue of
lin-3 by microinjecting genomic subclones in the vicinity of two
lin-3 RFLPs, syP1 and syP2. lambda PS#2 rescues the lethal phenotype of the
lin-3 lethal alleles
n1059,
s751,
sy51,
sy52, and
sy53. lambda PS1, lambda PS2, and pRH9 can all rescue the vulvaless phenotype of
lin-3. Surprisingly these transgenes also cause a variable fraction of
lin-3(+), and
lin-3(null) animals to a have a multivulva (Muv) phenotype. The multivulva phenotype could be caused by over-expression of wildtype
lin-3 or some mutant effect of the transgenic
lin-3 DNA. pRH10 and pRH22 have no ability to rescue and do not cause a multivulva phenotype. pRH19, which is a truncated derivative of pRH9, rescues less well than pRH9. pRH19 was used to isolate a
lin-3 cDNA because it does not overlap the poxy and abundant
fol-1 (friend of
lin-3) transcript (which was previously detected by reverse northern analysis and shown to reside in a region not necessary for rescue of
lin-3). The
lin-3 cDNA was isolated from a library made by Chris Martin. This cDNA detects both
lin-3 RFLPs on southern blots and is single copy in the genome. The 3' end of this cDNA extends outside of pRH19 but is within pRH9. We conclude that pRH9 contains the
lin-3 coding region and that pRH19 is a crippled 3' deletion of the gene. We are sequencing
lin-3 and examining the genetic properties of the transgenic
lin-3 Muvs.[See Figure 1]