THE ACTIVITY OF DROSOPHILA HAIRLESS IS REQUIRED IN PUPAE BUT NOT IN EMBRYOS TO INHIBIT NOTCH SIGNAL-TRANSDUCTION

Drosophila Hairless (H) encodes a negative regulator of Notch signalli ng. H activity antagonizes Notch (N) signalling during bristle develop ment at the pupal stage. We show here by clonal analysis that H acts b y inhibiting signal transduction rather than by promoting signal produ ction, during both selection of microch aete precursors in the notum a nd vein cell differentiation in the wing. Allele-specific interactions further suggest that H inhibits Notch signal transduction by interact ing directly with Suppressor of Hairless. Unexpectedly, this regulator y function of H appears to be essential only during imaginal developme nt. Using a null allele of H that corresponds to a deletion of the H c oding sequence, we show that embryos devoid of both maternal and zygot ic gene products develop similarly to wild-type embryos, Thus, H activ ity is not strictly required to regulate N-mediated cell fate choices in the embryo.