Anterior Hox Genes and the Process of Cephalization

© 2021 Hombría, García-Ferrés and Sánchez-Higueras.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.This work was supported by grant P20-00003 of the Junta de Andalucía, and grants BFU2016-76528-P and PID2019-104656GB-I00 of the Spanish MICINN/MINECO/FEDER to JH and by the MDM-2016-0687 María de Maeztu Research Excellence Award from the Agencia Estatal de Investigación to the Department of Gene Regulation and Morphogenesis at the CABD. MG-F was supported by FPI studentship BES-2017-081120 from MICINN.Peer reviewe