Meeting Abstract
34.5 Jan. 5 SoxE genes in development and evolution of the pharynx MCCAULEY, D.W.; University of Oklahoma dwmccauley@ou.edu
The neural crest is a defining characteristic of vertebrates that gives rise to many characters specific to vertebrates and are considered a hallmark of vertebrate evolution. In gnathostome vertebrates, derivatives of the neural crest include the jaws and pharyngeal skeleton. Since jawed vertebrates arose from a jawless ancestor, jawless lampreys provide an important proxy for the study of evolution of the pharyngeal skeleton. Cartilage of the pharyngeal skeleton in jawed vertebrates is composed of type II collagen (Col2a1) whose expression is driven by Sox9, a member of the SoxE subfamily. We have found that three SoxE paralogs are expressed in the pharynx. Although adult lamprey cartilage is not composed of Col2a1, SoxE1 and SoxE2 are expressed in the cartilage cells of the developing pharyngeal skeleton Interestingly, SoxE3, the lamprey paralog most closely related to gnathostome Sox9, is expressed in the branchial arch mesenchyme but not in the cartilage cells. The velum derived from the 1st branchial arch shows expression of SoxE3, but SoxE1 and SoxE2 expression are absent. Morpholino knockdown of the SoxE1 protein affected expression of SoxE2 and development of the pharyngeal skeleton, but development of the 1st arch was not affected. Since the 1st branchial arch forms the jaws of gnathostomes, these results suggest the duplication of SoxE genes may have been important for the evolution of jaws. We are continuing to investigate the role of SoxE genes in the development of the pharyngeal skeleton. A recent description of lamprey SoxE3 and Col2a1 expression in the pharynx suggested an ancient origin for the role of Sox9 in driving Col2a1 expression. We show here that SoxE3 expression does not overlap with that of Col2a1, suggesting further steps were required for the acquisition of Sox9 regulation of type II collagen expression in the pharyngeal skeleton of early jawed vertebrates.
