Meeting Abstract

65.1  Wednesday, Jan. 6  Of mice and fish: expression of lung morphogenesis genes in the actinopterygian swimbladder CASS, AN*; SERVETNICK, MD; MCCUNE, AR; Cornell University; University of Washington, Bothell; Cornell University anc24@cornell.edu

A defining but often ignored synapomorphy of osteichthyes is the presence of an air-filled organ, either lungs as in tetrapods and several fishes or swimbladders of certain rayfin and lobefin fishes. Lungs and swimbladders have long been hypothesized to be homologous because of their similar function, development, anatomy and phylogenetic distribution. Though the molecular development of lungs is well studied, swimbladder development remains largely ignored. Here we ask to what extent is the gene regulatory network deployed during early lung development also involved in early swimbladder development? We have investigated the expression of the zebrafish homologs to mouse TTF-1 (Danio Nkx2.1a and Nkx2.1b), HNF3β (Danio FoxA2) and Wnt7b, three integral factors which synergistically modulate early lung development. Using reverse-transcriptase PCR and whole-mount in situ hybridization, we show that these factors have the same expression pattern in developing and adult zebrafish swimbladder as in tetrapod lungs. Preliminary results show the same basic, but somewhat modified, pattern of gene expression in other phylogenetically relevant fishes. Similar patterns of expression in mouse lung and zebrafish swimbladder suggest that at least the same genetic “cassette” is involved in the early budding of these two kinds of air-filled organ. The phylogenetic distribution of the same basic expression pattern in both swimbladders and lungs across both the Sarcopterygii and Actinopterygii, is consistent with the previously postulated phylogenetic hypothesis that lungs and swimbladders are homologous at the level of Osteichthyes.