title: Novel function of the class I bHLH protein Daughterless in the negative regulation of proneural gene expression in the Drosophila eye.
abstract: Two types of basic helix-loop-helix (bHLH) family transcription factor have functions in neurogenesis. Class II bHLH proteins are expressed in tissue-specific patterns, whereas class I proteins are broadly expressed as general cofactors for class II proteins. Here, we show that the Drosophila class I factor Daughterless (Da) is upregulated by Hedgehog (Hh) and Decapentaplegic (Dpp) signalling during retinal neurogenesis. Our data suggest that Da is accumulated in the cells surrounding the neuronal precursor cells to repress the proneural gene atonal (ato), thereby generating a single R8 neuron from each proneural cluster. Upregulation of Da depends on Notch signalling, and, in turn, induces the expression of the Enhancer-of-split proteins for the repression of ato. We propose that the dual functions of Da--as a proneural and as an anti-proneural factor--are crucial for initial neural patterning in the eye.
authors.affiliation: Department of Molecular and Cellular Biology, University of Texas Health Science Center at Houston, Houston, Texas 77030, USA.
authors.forename: Janghoo
authors.initials: J
authors.lastname: Lim
authors.forename: Hamed
authors.initials: H
authors.lastname: Jafar-Nejad
authors.forename: Ya-Chieh
authors.initials: YC
authors.lastname: Hsu
authors.forename: Kwang-Wook
authors.initials: KW
authors.lastname: Choi