Hox genes are found throughout the animal kingdom; these regulatory genes play an important role throughout development, ensuring that our limbs grow in the right places, for example. In this study, scientists from France, the Netherlands, Portugal and the UK investigated the role of Hox genes in the development of the genes of the spine.
Normally, switching the Cdx genes off causes the growth of the embryo at the tail end to come to a halt. However, this new research shows that the Hox genes are able to take over and restore growth and ensure that the correct number of somites (and thus vertebrae) is produced. 'We now show that the activation of Hox genes is also part of how Cdx genes promote growth of the embryo at its tail end,' explained Moises Mallo of the Instituto Gulbenkian de Ciência in Portugal.
http://www.igc.gulbenkian.pt/research/unit/48