Gill developmental program in the teleost mandibular arch

Abstract

Whereas no known living vertebrate possesses gills derived from the jaw-forming mandibular arch, it has been proposed that the jaw arose through modifications of an ancestral mandibular gill. Here we show that the zebrafish pseudobranch, which regulates blood pressure in the eye, develops from mandibular arch mesenchyme and first pouch epithelia and shares gene expression, enhancer utilization, and developmental gata3 dependence with the gills. Combined with work in chondrichthyans, our findings in a teleost fish point to the presence of a mandibular pseudobranch with serial homology to gills in the last common ancestor of jawed vertebrates, consistent with a gill origin of vertebrate jaws.

The pseudobranch of jawed vertebrates is a mandibular arch-derived gill

“…We are therefore left in the somewhat difficult position of weighing limited, indirect evidence of ancestral mandibular arch anatomy and function from fossils against the striking anatomical and developmental similarities between the mandibular and gill arches of some extant taxa. We can now confidently infer that a gill-like pseudobranch is an ancestral feature of the gnathostome mandibular arch, based on our findings here and on parallel work in zebrafish, which demonstrates a mandibular arch origin of the pseudobranch as well as shared gene expression features, cis-regulatory elements and gata3 dependence with gills ( Thiruppathy et al, 2022 ). A spiracular cartilage and branchial rays, on the other hand, can (at present) only be resolved to the chondrichthyan stem.…”