Molecular genetic control of cell patterning and fate determination in the developing ventral spinal cord.

The generation of neuronal diversity in the ventral spinal cord during development is a multistep process that occurs with precise and reproducible spatiotemporal order. The proper functioning of the central nervous system requires that this be carried out with extraordinary precision from the outset. Extrinsic influences such as the secreted Sonic hedgehog (SHH) protein provide positional cues that are read out genetically as specific patterns of gene expression in subsets of dividing progenitors, which is the first overt indication that they have begun to embark upon cell-type-specific differentiation programs. Cells generated from these segregated domains will ultimately share similar properties and functions. Recent work illustrates that SHH, which regulates target genes via the GLI transcription factors, directly controls a subset of progenitor fate determinant genes and that both derepression and activation play a role in shaping the differential response to this morphogen.