Novel function of the class I bHLH protein Daughterless in the negative regulation of proneural gene expression in the Drosophila eye

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

Proximal–distal axis formation in the Drosophila leg

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Role of the TAB2-related protein TAB3 in IL-1 and TNF signaling

The cytokines IL-1 and TNF induce expression of a series of genes that regulate inflammation through activation of NF-κB signal transduction pathways. TAK1, a MAPKKK, is critical for both IL-1- and TNF-induced activation of the NF-κB pathway. TAB2, a TAK1-binding protein, is involved in IL-1-induced NF-κB activation by physically linking TAK1 to TRAF6. However, IL-1-induced activation of NF-κB is not impaired in TAB2-deficient embryonic fibroblasts. Here we report the identification and characterization of a novel protein designated TAB3, a TAB2-like molecule that associates with TAK1 and can activate NF-κB similar to TAB2. Endogenous TAB3 interacts with TRAF6 and TRAF2 in an IL-1- and a TNF-dependent manner, respectively. Further more, IL-1 signaling leads to the ubiquitination of TAB2 and TAB3 through TRAF6. Cotransfection of siRNAs directed against both TAB2 and TAB3 inhibit both IL-1- and TNF-induced activation of TAK1 and NF-κB. These results suggest that TAB2 and TAB3 function redundantly as mediators of TAK1 activation in IL-1 and TNF signal transduction