Axial specification in higher vertebrates.

The specification of the body axis in the embryo is reflected in the structure of the vertebral column. Expression patterns of Hox genes in the prevertebrae suggest their involvement in this specification process and in the maintenance of vertebral identities. A single, ectopically expressed Hox gene can reprogramme the rostral part of the vertebral column and induce phenotypic alterations interpretable as homeotic transformations.