THE basic–helix–loop–helix (bHLH) proteins constitute a class of transcription factors thought to be important in the control of cell-type determination1. These transcription factors are believed to activate the expression of cell-type-specific genes to generate stable differentiated cell types2. The expression of bHLH proteins, in turn, is regulated by spatial cues, so that switches in cell type occur in a reproducible pattern3. We report here that the lin-32 gene of Caenorhabditis elegans which encodes a bHLH protein of the Drosophila achaete-scute family of transcription factors, is necessary and in some cells sufficient for specification of the neuroblast cell fate. Similarity in the function and structure of the lin-32 protein (LIN-32) to transcription factors of the achaete-scute gene family in Drosophila and vertebrates implies that this class of transcription factors functioned in a primitive ancestral form to specify neuronal cell fate, supporting the proposition that certain basic mechanisms of cell-type determination have been conserved through metazoan evolution1.
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