Relationships between extramacrochaetae and Notch signalling in Drosophilawing development

The function of extramacrochaetae is required during the development of the Drosophila wing in processes such as cell proliferation and vein different iation. extramacrochaetae encodes a transcription factor of the HLH family, but unlike other members of this family, Extramacrochaetae lacks the basic region that is involved in interaction with DNA, Some phenotypes caused by extramacrochaetae in the wing are similar to those observed when Notch sig nalling is compromised. Furthermore, maximal levels of extramacrochaetae ex pression in the wing disc are restricted to places where Notch activity is higher, suggesting that extramacrochaetae could mediate some aspects of Not ch signalling during wing development, We have studied the relationships be tween extramacrochaetae and Notch in wing development, with emphasis on the processes of vein formation and cell proliferation. We observe strong gene tic interaction between extramacrochaetae and different components of the N otch signalling pathway, suggesting a functional relationship between them. We show that the higher level of extramacrochaetae expression coincides wi th the domain of expression of Notch and its downstream gene Enhancer of sp lit-m beta. The expression of extramacrochaetae at the dorso/ventral bounda ry and in boundary cells between veins and interveins depends on Notch acti vity. We propose that at least during vein differentiation and wing margin formation, extramacrochaetae is regulated by Notch and collaborates with ot her Notch-downstream genes such as Enhancer of split-m beta.