MOLECULAR MECHANISMS OF SEGMENTAL PATTERNING IN THE VERTEBRATE HINDBRAIN AND NEURAL CREST

Recent work has shown that segmentation underlies the patterning of th e vertebrate hindbrain and its neural crest derivatives. Several genes have been identified with segment-restricted expression, and evidence is now emerging regarding their function and regulatory relationships . The expression patterns of Hox genes and the phenotype of null mutan ts indicate roles in specifying segment identity. A zinc finger gene K rox-20 is a segment-specific regulator of Hox expression, and it seems probable that retinoic acid receptors also regulate Hox genes in the hindbrain. The receptor tyrosine kinase gene Sek may mediate cell-cell interactions that lead to segmentation. These studies provide a start ing point for understanding the molecular basis of segmental patternin g in the hind-brain.