The nervous system consists of strikingly diverse cell types, which can be classified by first grouping together neurons with shared features, and then subdividing these groups according to specific characteristics. But is the specification of neuronal types and subtypes linked and, if so, how? On , Oliver Hobert and colleagues reveal that, in C. elegans, the transcription factor CHE-1, which specifies the two ASE taste receptor neurons, is also required for their subsequent subtype specialisation into ASEL and ASER. By analysing the promoter regions of four genes differentially expressed in ASEL and ASER,the authors show that the cis-regulatory regions of several of these genes act as repressors or co-activators of CHE-1. In addition, the affinity of CHE-1 for its targets plays a role in restricting its activity to ASEL or ASER, and thus in controlling neuronal subtype specification. The cis-regulatory mechanisms involved are surprisingly diverse, and future work should shed light on the upstream events that lead to their differential activity.
