Transcriptional regulation of vertebrate Hox genes during embryogenesis

The identification in transgenic mice of Hox gene DNA regulatory elements that can recapitulate certain aspects of the endogenous gene's expression pattern has proceeded with great success. However, perfect reproduction of the correct expression pattern 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. Currently, four groups of transcriptional regulators have been identified that have been shown to directly regulate Hox gene expression in the vertebrate embryo: retinoic acid receptors, Krox20, members of the Pbx/exd family, and the Hox genes themselves.