Meeting Abstract

135.6  Monday, Jan. 7  Are swimbladders inverted lungs? Evidence from developmental genetics CASS, AN*; MCCUNE, AR; Cornell University; Cornell University anc24@cornell.edu

The homology of lungs and swimbladders has been accepted to varying degrees by the great morphologists of the 19th and 20th centuries. We have recently shown that a shared developmental regulatory network underlies the early development of tetrapod lungs and the zebrafish swimbladder. This is the first genetic evidence supporting this proposed structural homology. One major unresolved incongruity regarding lung and swimbladder homology is that lungs bud ventrally from the gut while swimbladders bud dorsally, leading some to the conclusion that lungs and swimbladders are not structurally homologous, but rather independent modifications of the posterior pharynx. However, comparative developmental biology has shown that a seeming structural inversion, such as the ventral to dorsal inversion of the nervous system in bilaterian invertebrates and chordates, can be due to an inversion of the ancestral patterning mechanism and not an independent structural origin. The developmental genetic mechanism specifying the ventral location of the tetrapod lung bud is well understood, and involves the mutual antagonism of the lung-specifying gene Nkx2.1 and its mutual antagonist Sox2. Our study examines the expression pattern of these two genes in the posterior pharynx and swimbladder bud in zebrafish. An inversion of the ancestral lung patterning mechanism would be strong evidence for the structural homology of these two structures and addresses a longstanding and controversial issue in comparative anatomy.