Deconstructing cell determination: proneural genes and neuronal identity

Vertebrates express scores of bHLH proteins during neural development. Earl ier studies inspired by the established role of "proneural" genes in fly ne urogenesis, as well as by the vertebrate bHLH myogenic program, focused on the reconstruction of bHLH gene cascades, which are thought to control succ essive steps leading to neuronal differentiation. Little attention has been paid thus far to the relationship between the diversity of neural bHLH gen es and the diversity of neuronal phenotypes. This article reviews recent ev idence that, akin to their fly counterparts, vertebrate neural bHLH genes p robably confer not only "generic" neuronal properties, but also neuronal ty pe-specific properties, inextricably linking neural determination and the s pecification of neuronal identity. We also speculate on the relations betwe en positional information and gene activity, and on the evolutionary signif icance of the diversity of bHLH genes. BioEssays 21:313-318, 1999. (C) 1999 John Wiley & Sons, Inc.