REGULATION OF VERTEBRATE NEURAL CELL FATE BY TRANSCRIPTION FACTORS

Evidence that region- and cell-type-specific transcription factors reg ulate morphogenesis and differentiation of the vertebrate nervous syst em comes from numerous studies, including descriptions of discrete pat terns of expression during neural development and analysis of mutant p henotypes. Recently published works provide insights into the roles of vertebrate transcription factors in regulating the generation of neur al precursors, regionalization of the nervous system, and subsequent d ifferentiation of specific cell types within these regions. For instan ce, misexpression studies in Xenopus embryos show that the newly isola ted basic helix-loop-helix protein NeuroD is able to promote neurogene sis, whereas analysis of mouse embryos mutant for the homeobox gene En -1 demonstrates that this transcription factor is required for proper development of the midbrain-hindbrain region. A recent study in chick shows that the combinatorial expression of Islet-1, Lim-1, and two oth er LIM homeobox genes, Islet-2 and Lim-3, defines subclasses of motor neurons in the spinal cord, supporting a model where combinatorial rep ertoires of transcription factors may act to generate diverse cell typ es.