Subcellular localization of Suppressor of Hairless in Drosophila sense organ cells during Notch signalling.

During imaginal development of Drosophila, Suppressor of Hairless [Su(H)], an evolutionarily conserved transcription factor that mediates intracellular signalling by the Notch (N) receptor, controls successive alternative cell fate decisions leading to the differentiation of multicellular sensory organs. We describe here the distribution of the Su(H) protein in the wing disc epithelium throughout development of adult sense organs. Su(H) was found to be evenly distributed in the nuclei of all imaginal disc cells during sensory organ precursor cells selection. Thus differential expression and/or subcellular localization of Su(H) is not essential for its function. Soon after division of the pIIa secondary precursor cell, Su(H) specifically accumulates in the nucleus of the future socket cell. At the onset of differentiation of the socket cell, Su(H) is also detected in the cytoplasm. In this differentiating cell, N and deltex participate in the cytoplasmic retention of Su(H). Still, Su(H) does not colocalize with N at the apical-lateral membranes. These observations suggest that N regulates in an indirect manner the cytoplasmic localization of Su(H) in the socket cell. Finally, the pIIb, shaft and socket cells are found to adopt invariant positions along the anteroposterior axis of the notum. This raises the possibility that tissue-polarity biases these N-mediated cell fate choices.