Hox genes control homocercal caudal fin development and evolution

• Published in: Science advances 2024-01, Vol.10 (3), p.eadj5991-eadj5991
• Main Authors: Cumplido, Nicolás, Arratia, Gloria, Desvignes, Thomas, Muñoz-Sánchez, Salomé, Postlethwait, John H, Allende, Miguel L
• Format: Article
• Language: English
• Subjects: Animal Fins; Animals; Biological Evolution; Genes, Homeobox; Spine; Zebrafish - genetics
• ISSN: 2375-2548; 2375-2548
• DOI: 10.1126/sciadv.adj5991

Ancient bony fishes had heterocercal tails, like modern sharks and sturgeons, with asymmetric caudal fins and a vertebral column extending into an elongated upper lobe. Teleost fishes, in contrast, developed a homocercal tail characterized by two separate equal-sized fin lobes and the body axis not extending into the caudal fin. A similar heterocercal-to-homocercal transition occurs during teleost ontogeny, although the underlying genetic and developmental mechanisms for either transition remain unresolved. Here, we investigated the role of genes in caudal fin formation as these genes control posterior identity in animals. Analysis of expression profiles of zebrafish paralogs and phenotypes of CRISPR/Cas9-induced mutants showed that double and mutants fail to form a caudal fin. Furthermore, single mutants display heterocercal-like morphologies not seen since Mesozoic fossil teleosteomorphs. Relaxation of functional constraints after the teleost genome duplication may have allowed duplicates to neo- or subfunctionalize, ultimately contributing to the evolution of a homocercal tail in teleost fishes.