Hox Genes and Segmental Patterning of the Vertebrate Hindbrain

SYNOPSIS. Pattern formation in the developing hindbrain and cranio-facial region has been studied in a range of vertebrate organisms. The developing hindbrain is transiently segmented into units termed rhombomeres which correspond with domains of gene expression, lineage restriction and neuronal organization and serve to coordinate the migration of cranial neural crest into the adjacent branchial arches. In this paper I review the cellular and molecular events underlying both hindbrain segmentation and the acquisition of segmental identity, consolidating recent results from different model systems. Data suggesting that the vertebrate Hox genes play an important role in specifying positional value to the rhombomeres and cranial neural crest are also examined. I compare expression patterns of the Hox genes between species and consider the mechanisms involved in controlling their appropriate spatial regulation. In addition I describe a recently characterized zebraflsh hindbrain segmentation mutant, Valentino; morphological, cellular and gene expression data for this mutant are helping to further our understanding of hindbrain patterning.