egl-18 and
elt-6, adjacent genes encoding GATA factors, are redundantly required for seam cell development and vulval development.1,2
egl-18 chromosomal mutants, in which
elt-6 is presumably active, show partially penetrant lethality and relatively mild defects in vulval development. In contrast, RNA-mediated interference (RNAi) of both
egl-18 and
elt-6 activity results in fully penetrant lethality, and animals rescued for lethality by a transgene with a partial promoter show a strong vulvaless phenotype: vulval precursor cells (VPCs) often fuse with the surrounding epidermis or undergo fewer than normal number of cell divisions. nT1 was isolated in a screen for vulvaless mutants, and is a reciprocal translocation between chromosomes IV and V.3 Examination of nT1 homozygous animals carrying a transgenic
ajm-1::GFP adherens junction marker indicates that most VPCs fuse with the surrounding epidermis in the late L2 and early L3 stages. nT1 mutants are thin and grow slowly, but exhibit only a small percentage of lethality. Because the nT1 vulval phenotype resembled that observed in
egl-18/elt-6 RNAi animals, and because an nT1 breakpoint was mapped near
egl-18/elt-6 on LGIV,4 we hypothesized that the nT1 phenotypes might be due to a disruption of
egl-18 and
elt-6 function in the vulva. Two lines of evidence support the hypothesis. First, nT1 does not complement
egl-18: nT1/egl-18 animals exhibit an intermediate level of vulval defects. Second, through a series of PCR analyses and a subsequent inverse-PCR analysis, we have located the breakpoints of nT1 near
egl-18 on LGIV, approximately 12Kb upstream of the
egl-18 ATG, and in the
act-3 gene on LGV. Our hypothesis is that there is an important vulval enhancer for
egl-18/elt-6 further upstream of the nT1 breakpoint. We are currently attempting to find the possible vulval enhancer by examining expression patterns of a series of enhancer constructs and testing
egl-18 transgenes for rescue of the nT1 vulvaless phenotype. If nT1 indeed represents a vulva-specific
egl-18 elt-6 double mutant, it will confirm previous RNAi results suggesting that EGL-18 and ELT-6 are important regulators of cell fusion and fates in the vulva,2 and will be very useful in helping us understand the role these GATA factors play during vulval development.