Figure 5.

(a–d) Tbx1 is not expressed in the pharyngeal gill pores or pharyngeal arches of Saccoglossus kowalevskii, though (e–h) FoxC is expressed in the gill pore epithelium. (a) At the neurula stage, Tbx1 is expressed panectodermally, excluding the ciliary band. Expression of Tbx1 is not detected at the (b) one-, two- (not shown), (c) three- or (d) four-gill-pore stages. (e) At the neural stage, FoxC is expressed at the presumptive proboscis–collar boundary, and in the presumptive first gill pore endoderm. Expression of FoxC is subsequently detected in the epithelium of the developing (f) first, second (not shown), (g) third and (h) fourth gill pores. In all images, animals are oriented with anterior to the upper left. Scale bar in (a): 50 µm. All images to same scale.