Monday, April 20, 2015 -
12:00pm to 1:00pm
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MCZ 101 Seminar Room, 26 Oxford Street, Cambridge

MCZ Lunchtime Seminar

"The deep homology of the autopod: evolution of regulatory systems in vertebrate appendage development" with Andrew R. Gehrke, Graduate Student, Shubin Lab, Department of Organismal Biology and Anatomy, The University of Chicago

Abstract: The evolution of the autopod (wrist/ankle and digits) in the limbs of tetrapod vertebrates represents a key morphological innovation that was crucial for the colonization of land.  While the fossil record suggests that the wrist and digits formed though the progressive elaboration of the distal endoskeleton of the fin, there is no obvious morphological counterpart to the autopod in living fishes.  Thus, comparative molecular data may provide insight into understanding both the homology of vertebrate appendages as well as the genetic processes behind the fin to limb transition. Mammalian limbs are built by two sequential periods of Hox gene activation, referred to as "early" and "late" phases that pattern proximal (arm) and distal (hand) segments, respectively.  The regulatory systems responsible for the dual nature of Hox gene expression in limbs have been extensively studied in mouse, where early and late phase enhancers lie on opposite sides of the HoxD and HoxA clusters.  We asked if fish genomes contain orthologs of these "arm" and "digit" enhancers.  Using multiple sequence alignments with key taxa combined with epigenomic profiling, we identified both "early" and "late" phase Hox enhancers in the genome of a variety of fish species.  When tested in transgenic zebrafish, these regulatory elements drove reporter expression in pectoral fins reminiscent of the biphasic pattern in mouse limbs.  Furthermore, when tested in transgenic mice, enhancers from specific fish were able to drive expression in an identical pattern to their murine orthologs.  Altogether, these data suggest an ancient origin of the vertebrate Hox appendage developmental system, implying homology between the distal bones of fish fins and the wrist/digits of tetrapods.

Contact Name: 

Catherine Weisel

Research Areas: 

Harvard University
Center for the Environment

Address: 26 Oxford Street, 4th Floor, Cambridge
Phone: (617) 495-0368

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