Hox homeobox genes and regionalisation of the nervous system.

The Hox family of homeobox-containing genes are intimately associated with the processes of axial patterning in vertebrate embryos. This family of transcription factors is widely conserved in evolution and by analogy with their Drosophila counterparts, the HOM-C homeotic genes, may play a role in establishing regional identity in a number of embryonic systems, including the CNS. The patterns of expression of these genes are linked with the generation of rhombomeres and neural crest in the developing hindbrain, and suggest that they provide a molecular system for generating a combinatorial patterning mechanism. Analysis of mouse Hox mutants generated by homologous recombination have clearly demonstrated that the genes have important roles in normal regionalisation of the hindbrain and branchial arches, and this has lead to interest in how their early patterns are established in the nervous system. The Hox genes and their relation to hindbrain segmentation therefore provide a means of examining the cascade of events which regulates pattern formation in early neural development.