Homeobox genes in the developing central nervous system.

A number of genes containing sequences coding for DNA-binding domains homologues to homeobox sequences in Drosophila have been isolated in vertebrate and their mechanism of action have been studied. In Particular Hox family genes share with Drosophila homeotic genes a genomic organization in gene clusters and an expression pattern that is similar in a number of important respects. In situ hybridization experiment have shown that there is a strict correspondence, or collinearity, between the order of the Hox genes (3' to 5') within the chromosomal cluster and that of their expression domains (anterior to posterior) in the embryo. Recent data obtained in embryonal carcinoma (EC) cells induced to differentiate by retinoic acid (RA) cast some light on the molecular mechanisms underlying the collinear expression of the Hox genes.