biphasic hoxd gene expression in shark paired fins reveals an ancient origin of the distal limb domain两相的hoxd基因表达在鲨鱼鳍配对显示远端肢体域的一个古老的起源.pdfVIP

Biphasic Hoxd Gene Expression in Shark Paired Fins Reveals an Ancient Origin of the Distal Limb Domain 1¤ 1 1,2 Renata Freitas , GuangJun Zhang , Martin J. Cohn * 1 Department of Zoology, Cancer/Genetics Research Complex, University of Florida, Gainesville, Florida, United Sates of America, 2 Department of Anatomy and Cell Biology, Cancer/Genetics Research Complex, University of Florida, Gainesville, Florida, United States of America The evolutionary transition of fins to limbs involved development of a new suite of distal skeletal structures, the digits. During tetrapod limb development, genes at the 59 end of the HoxD cluster are expressed in two spatiotemporally distinct phases. In the first phase, Hoxd9-13 are activated sequentially and form nested domains along the anteroposterior axis of the limb. This initial phase patterns the limb from its proximal limit to the middle of the forearm. Later in development, a second wave of transcription results in 59 HoxD gene expression along the distal end of the limb bud, which regulates formation of digits. Studies of zebrafish fins showed that the second phase of Hox expression does not occur, leading to the idea that the origin of digits was driven by addition of the distal Hox expression domain in the earliest tetrapods. Here we test this hypothesis by investigating Hoxd gene expression during paired fin development in the shark Scyliorhinus canicula, a member of the most basal lineage of jawed vertebrates. We report that at early stages, 59Hoxd genes are expressed in anteroposteriorly nested patterns, consistent with the initial wave of Hoxd transcription in teleost and tetrapod paired appendages. Unexpectedly, a second phase of expression occurs at later stages of shark fin development, in which Hoxd12 and Hoxd13 are re-expressed along the distal margin of the fin buds. This second phase is similar to that obser