Abstract

Pharyngeal arches are an integral feature of the embryonic vertebrate head, generating much of the craniofacial skeleton. In this talk I will give a broad introduction to vertebrate pharyngeal and gill arch development and outline my recent findings on the role of Wnt signalling in the gill arches of the little skate. The gill arch skeleton of cartilaginous fishes (sharks, skates, rays and holocephalans) exhibit clear anterior–posterior polarity, with a series of appendages (branchial rays) forming in the gill arch posterior. Branchial rays derive from a posterior domain of gill arch mesenchyme, which is responsive to Shh signalling from a distal signalling centre called the gill arch epithelial ridge (GAER) (Gillis and Hall, 2016). However, how the branchial rays are specified exclusively within the posterior gill arch is not known. Using RNAseq, we discover that several Wnt genes are expressed adjacent to the GAER , and that these Wnt signals are transduced largely in the anterior gill arch. Finally, we show that loss of Wnt signalling results in the formation of ectopic anterior branchial rays. Our findings demonstrate that Wnt signalling restricts cartilage formation to the posterior gill arch, highlighting the importance of these signalling interactions for cell fate determination.