Studies of vulval development would be greatly aided by the availability of promoters that drive gene expression specifically in vulval precursor cells (VPCs). One not quite VPC-specific but still useful promoter is that of the
lin-31 gene (Tan et al., 1998). P. Tan and S. Kim generously provided us with the PB255 version of the
lin-31 promoter, which drives heterologous gene expression in Pn.p cells (including the VPCs) and a limited number of additional cells (mostly neurons). We have been using this promoter ("
plin-31") to drive the vulval expression of various
ksr-1 variants (*), and as a control, we have also analyzed a
plin-31::GFP transgene. When injected into N2 at concentrations of 50-100 ng/l, these transgenes dont have many obvious detrimental effects. However, we find that integrated arrays of our experimental and control transgenes sometimes cause a
bar-1-like phenotype (Eisenmann et al., 1998) in which some VPCs never divide but rather adopt a "quaternary" or "fused" fate. The severity of this phenotype varies from line to line, but can be quite strong in some cases (e.g. one
plin-31::KSR-1* line had 88% abnormal animals, n=36). Since we also see a weak
bar-1 like phenotype in a control
plin-31::GFP line (9% abnormal animals, n=22), we suspect that this phenotype could have less to do with
ksr-1 than with high levels of
lin-31 regulatory sequences (perhaps titrating out other factors such as BAR-1 or LIN-39). We advise other users to be cautious in interpreting similar defects caused by other
plin-31 constructs.