Transcriptional control of Hox genes in the vertebrate nervous system.

The identification, in transgenic mice, of Hox gene DNA regulatory elements that can recapitulate certain aspects of the endogenous gene expression pattern has proceeded with great success. Perfect reproduction of the correct expression pattern, however, is uncommon, even when large genomic fragments spanning neighboring genes are analyzed, suggesting that important regulatory regions may be located at large distances from the genes they control or that their specific context may be important. Four classes of transcriptional regulators have been identified recently that have been shown to directly regulate Hox gene expression in the murine nervous system: retinoic acid receptors, Krox20, the Pbx/exd family, and the Hox genes themselves.