The emergence of the evo-devo discipline is largely due to the characterization of the Hox gene family in several animal species. In this sixth lecture, after a brief history of the milestones that led to the cloning of these genes in insects and then in vertebrates, I review current knowledge of their phylogenetic origin, appearance, evolution and presence in metazoans.
These Hox genes, which belong to a subfamily of genes containing a "homeobox", are unique in their regulation in that the temporal and spatial specificities of their expression are determined by their respective positions within genomic clusters (four dense groups of genes distributed on different chromosomes), a phenomenon often referred to as "spatial and temporal colinearities". This phenomenon is described, along with its impact on both the structural evolution of this Hox gene family and the constraints it imposes on embryo development. The theoretical importance of this system is analyzed, in particular concerning the effects of such in-cis meta-regulations on genome evolutionary dynamics.
