From skin to nerve: flies, vertebrates and the first helix

Vertebrate and invertebrate nervous tissue is derived from early embryonic ectoderm, which also gives rise to epidermal derivatives such as skin. Proneural basic helix-loop-helix (bHLH) transcription factors are the key players in the formation of peripheral nervous system (PNS) and central nervous system (CNS) from naive ectoderm to differentiated postmitotic neurons. The comparative approach and the use of a wide range of animal models have led to increasingly comprehensive investigations of this issue in the last decade. This review will focus on current studies of neural development in vertebrate and invertebrate PNS and on understanding how the bHLH domain structure encodes multiple functions required for neural specification.