Expression of and in dipnoan and teleost fins provides new insights into the evolution of vertebrate appendages.

Background: The concerted activity of and transcription factors is essential for the subdivision of tetrapod limbs into proximo-distal (PD) domains; however, little is know about the evolution of this patterning mechanism. Here, we aim to study the expression of and orthologues in the median and paired rayed fins of zebrafish and in the lobed fins of the Australian lungfish.

Results: First, a late phase of expression of and in zebrafish dorsal and anal fins relates with segmentation of endochondral elements in proximal and distal radials. Second, our zebrafish in situ hybridization results reveal spatial and temporal changes between pectoral and pelvic fins. Third, in situ analysis of , and genes in pectoral fins identifies decoupled domains of expression along the PD axis.

Conclusions: Our data raise the possibility that the origin of stylopod and zeugopod lies much deeper in gnathostome evolution and that variation in and expression has played a substantial role in the transformation of appendage anatomy. Moreover, these observations provide evidence that the / profile considered a hallmark of stylopod/zeugopod patterning is present in .