The presence of an embryonic opercular flap in amniotes

Richardson, Jo, Shono, Takanori, Okabe, Masataka and Graham, Anthony (2012) The presence of an embryonic opercular flap in amniotes. Proceedings of the Royal Society B: Biological Sciences, 279 (1727). ISSN 0962-8452

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The operculum is a large flap consisting of several flat bones found on the side of the head of bony fish. During development, the opercular bones form within the second pharyngeal arch, which expands posteriorly and comes to cover the gill-bearing arches. With the evolution of the tetrapods and the assumption of a terrestrial lifestyle, it was believed that the operculum was lost. Here, we demonstrate that an embryonic operculum persists in amniotes and that its early development is homologous with that of teleosts. As in zebrafish, the second pharyngeal arch of the chick embryo grows disproportionately and comes to cover the posterior arches. We show that the developing second pharyngeal arch in both chick and zebrafish embryos express orthologous genes and require shh signalling for caudal expansion. In amniotes, however, the caudal edge of the expanded second arch fuses to the surface of the neck. We have detailed how this process occurs and also demonstrated a requirement for thyroid signalling here. Our results thus demonstrate the persistence of an embryonic opercular flap in amniotes, that its fusion mirrors aspects of amphibian metamorphosis and gives insights into the origin of branchial cleft anomalies in humans.

Item Type: Article
Keywords: Operculum, Pharyngeal apparatus, Zebrafish
Schools and Departments: School of Life Sciences > Biochemistry
Subjects: Q Science > QL Zoology > QL0951 Embryology
Depositing User: Joanna Richardson
Date Deposited: 27 Jul 2016 15:28
Last Modified: 08 Mar 2017 05:05

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