Segment-specific expression of a zinc-finger gene in the developing nervous system of the mouse

The process of segmentation, in which repeated homologous structures are generated along the anterior-posterior axis of the embryo is a widespread mechanism in animal development. In vertebrates, segmentation is most apparent in the somites and the peripheral nervous system^1,2, but the existence of repetitive bulges, termed neuromeres, in the early neural epithelium of vertebrates suggests that the CNS may also be segmented^3-9. Consistent with this, cranial ganglia⁸ and certain neurons^8,10 are associated with specific hindbrain neuromeres. Here, we report that Krox-20 a zinc-finger gene, is expressed in two alternate neuromeres in the mouse early hindbrain. This pattern subsequently decays and Krox-20 is transiently expressed in specific hindbrain nuclei. In addition, Krox-20 is expressed in early neural crest cells, and then in the neural crest-derived boundary caps, glial components of the cranial and spinal ganglia. The demonstration that neuromeres are domains of gene expression provides molecular evidence for the segmentation of the CNS.