Meeting Abstract
12.6 Sunday, Jan. 4 A molecular footprint of limb development in the HoxA-13 gene: implications for the origin of urodele limb development WAGNER, Gunter P.*; KOHLSDORF, Tiana; GRIZANTE, Mariana; KIN, Koryu; Yale University; Universidade de S Paulo; Universidade de S Paulo; Yale University gunter.wagner@yale.edu
Transcription factor genes can undergo adaptive changes in their coding sequence when recruited into a novel developmental context. We use this fact as a rational to search for a molecular footprint of limb development and limb loss in the limb developmental gene HoxA-13. This gene is expressed during limb development in the prospective autopodium, male and female reproductive track, kidney and body axis. We sequenced a fragment of exon 1 of HoxA-13 genes from various squamates amphibians and fishes and compared the inferred amino acid sequences using the random forest method to search for amino acid residues that are indicative of the presence or absence of the autopodium. The classification of sequences in those from species with autopodium and those without reliably identifies all fishes and snakes as limbless, and all classical eu-tetrapods as limbed (turtle, alligator, anuran, mouse, chicken etc). We use this sequence signature to test the idea that urodele limb development is different from that of other tetrapods because of a transient period of limb loss in the stem lineage of uroldeles. Urodeles have several unique features to their limb development: the sequence of digit development is from anterior to posterior, the gene HoxA-11, normally restricted to the zeugopod, is expressed in developing digits, the gene HoxD-11, normally strongly expressed in the developing autopod, is only weakly expressed, and Shh, normally expressed long the posterior edge of the autopod, is restricted to a small spot in the posterior margin of the limb bud. We sequenced a large sample of amphibian species to compare their HoxA-13 sequences with that of clearly limbed and limbless and discuss the implications for the origin of urodele limb development.
