title: Homeosis and beyond. What is the function of the Hox genes?
abstract: What is the function of the Hox genes? At first glance, it is a curious question. Indeed, the answer seems so obvious that several authors have spoken of 'the Hox function' about some of the Hox genes, namely Hox3/zen and Hox6/ftz that seem to have lost it during the evolution of Arthropods. What these authors meant is that these genes have lost their 'homeotic' function. Indeed, 'homeotic' refers to a functional property that is so often associated with the Hox genes. However, the word 'Hox' should not be used to refer to a function, but to a group of genes. The above examples of Hox3/zen (see Schmitt-Ott's chapter, this book) and Hox6/ftz show that the homeotic function may be not so tightly linked to the Hox genes. Reversely, many genes, not belonging to the Hox group, do present a homeotic function. In the present chapter, I will first give a definition of the Hox genes. I will then ask what is the 'function' of a gene, examining its various meanings at different levels of biological organization. I will review and revisit the relation between the Hox genes and homeosis. I will suggest that their morphological homeotic function has been secondarily derived during the evolution of the Bilateria.
authors.affiliation: Developmental Biology, Pierre and Marie Curie University, Paris, France. jean.deutsch@snv.jussieu.fr
authors.forename: Jean S
authors.initials: JS
authors.lastname: Deutsch
mesh_terms: D000818:Animals; D005075:Biological Evolution; D019521:Body Patterning / Q000235:genetics*; D018507:Gene Expression Regulation, Developmental; D005801:Genes, Homeobox; D018398:Homeodomain Proteins / Q000235:genetics
chemical_list: D018398:Homeodomain Proteins