The animal nervous system contains many different types of neurons, but what mechanisms underpin the generation of such diversity? Now, Oliver Hobert and colleagues reveal that in C. elegans, the Tailless/TLX transcription factor (TF) NHR-67 controls both the neuronal cell fate and left-right (L/R) identity of the ASE class of gustatory neurons (see ). ASE neurons differentiate in stages: first, overall ASE identity is adopted; then,distinct left-hand (ASEL) and right-hand (ASER) cell types are specified. The authors isolate nhr-67 from a screen for mutants with perturbed L/R asymmetry and discover, surprisingly, that it also regulates overall ASE identity, in conjunction with the fate determinant che-1. Subsequently, nhr-67 promotes ASER specification by activating the homeobox gene cog-1 in both prospective ASER and ASEL neurons; in ASEL neurons, however, cog-1 activity is inhibited by the microRNA lsy-6. Such reiterative deployment of TFs, the authors suggest, might constitute a general feature of TF activity in the specification of neuronal subtypes.
