During vulval cell fate determination, the C.elegans Mi-2 chromatin remodelling proteins LET-418 and CHD-3 fulfil both shared and unique functions (1).
let-418 but not
chd-3, behaves like a synMuvB gene, but neither of them is a synMuvA gene. In
let-418;
chd-3 double mutants, 30% of the P5.p and 40 % of the P7.p descendants are detached from the hypodermal syncytium, indicating that these cells adopt a 1 or a 1/2 hybrid cell fate (1). Moreover, 25% of
let-418;
chd-3 double mutants have an induced P8.p. 30% of the
let-418 single mutants have an everted vulva, and 7% show an induced P8.p. This hyperinduced phenoptype of P5.p, P7.p and P8.p suggest that LET-418 and CHD-3 may negatively control the activity of important vulval specification genes. Since
lin-39 is known to play a key role in vulval cell fate specification, we have analysed its expression pattern in the Pn.p cells of
let-418;
chd-3 double mutants. In wild type L3 larvae, LIN-39 levels are high in P6.p, lower in P5.p/P7.p and basal in P3.p/P4.p/P8.p. Interestingly we found that in
let-418/chd-3 double mutants, LIN-39 expression was significantly increased in P5.p, P7.p and P8.p, reaching a level similar to the one of P6.p in wt animals. Furthermore, we observed that the absence of LET-418 in a
lin-39(rf) mutant background increased the frequency of animals with an everted vulva and decreased the frequency of vulvaless worms, suggesting that LET-418 acts upstream of or in parallel to LIN-39. Currently, we are testing the possibility that LET-418 and CHD-3 bind directly to the promoter region of
lin-39 to control its expression in the VPCs during vulva formation. The results will be discussed. (1) von Zelewsky, T. et al., 2000, Development 127, 5277-5287