Abstract
During evolution, bilateral animals have experienced a progressive process of cephalization with the anterior concentration of nervous tissue, sensory organs and the appearance of dedicated feeding structures surrounding the mouth. Cephalization has been achieved by the specialization of the unsegmented anterior end of the body (the acron) and the sequential recruitment to the head of adjacent anterior segments. Here we review the key developmental contribution of Hox1–5 genes to the formation of cephalic structures in vertebrates and arthropods and discuss how this evolved. The appearance of Hox cephalic genes preceded the evolution of a highly specialized head in both groups, indicating that Hox gene involvement in the control of cephalic structures was acquired independently during the evolution of vertebrates and invertebrates to regulate the genes required for head innovation.
Highlights
Centro Andaluz de Biología del Desarrollo (Consejo Superior de Investigaciones Científicas/Junta de Andalucía/Universidad Pablo de Olavide), Seville, Spain
Comparative analyses indicate that well developed clusters comprising at least seven Hox genes were already present more than 550 million years ago, suggesting their evolution was concurrent with the diversification of the main animal body plans that appeared during the Cambrian explosion
Additional structural and biochemical studies will help to decipher whether the CTM’s modulatory effect on HoxB1-Pbx interactions either creates a new range of binding preferences, or forces Labial to operate preferentially as a monomer in a context-dependent manner. Another case of paralog specificity has been described for the Sex combs reduced (Scr)/Hox5 paralog group, where it has been found that the interaction of Scr with their main DNA binding cofactor (Exd/Pbx) is necessary to recognize the DNA sequence, and the specific DNA shape of its target DNA backbone, which has a strong impact on both DNA binding strength and specificity
Summary
Centro Andaluz de Biología del Desarrollo (Consejo Superior de Investigaciones Científicas/Junta de Andalucía/Universidad Pablo de Olavide), Seville, Spain. Edited by: Ernesto Sánchez-Herrero, Severo Ochoa Molecular Biology Center (CSIC-UAM), Spain. Bilateral animals have experienced a progressive process of cephalization with the anterior concentration of nervous tissue, sensory organs and the appearance of dedicated feeding structures surrounding the mouth. We review the key developmental contribution of Hox genes to the formation of cephalic structures in vertebrates and arthropods and discuss how this evolved. The appearance of Hox cephalic genes preceded the evolution of a highly specialized head in both groups, indicating that Hox gene involvement in the control of cephalic structures was acquired independently during the evolution of vertebrates and invertebrates to regulate the genes required for head innovation
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