AUTHOR=Hombría James C.-G. , García-Ferrés Mar , Sánchez-Higueras Carlos TITLE=Anterior Hox Genes and the Process of Cephalization JOURNAL=Frontiers in Cell and Developmental Biology VOLUME=Volume 9 - 2021 YEAR=2021 URL=https://www.frontiersin.org/journals/cell-and-developmental-biology/articles/10.3389/fcell.2021.718175 DOI=10.3389/fcell.2021.718175 ISSN=2296-634X ABSTRACT=During evolution, bilateral animals have experienced a progressive process of cephalisation with the anterior concentration of nervous tissue, sensory organs and the appearance of dedicated feeding structures surrounding the mouth. Cephalisation has been achieved by the specialisation 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-Hox5 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 specialised head in both groups, indicating that Hox gene involvement in the control of cephalic structures was acquired independently during evolution in vertebrates and invertebrates to regulate the genes required for head innovation.