Molecular limb development in the basal squamate Hemidactylus

• Applicant: Dr. Constanze Bickelmann
• Subject Area: Evolutionary Cell and Developmental Biology (Zoology) ; Developmental Biology
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 274695956

The vertebrate limb has traditionally formed one of the cornerstones in evolutionary developmental biology, greatly contributing to our understanding of developmental processes and the deep homology of organ systems. In recent years, our knowledge of the origin, evolution and development of the vertebrate limb has gained a new scope due to a much broader taxonomic sampling of study animals of various vertebrate clades in addition to the well-known traditional model organisms mouse and chicken. Therein, taxa with extraordinary morphologies related to ecological specializations have immensely improved our knowledge of the origin and molecular basis of limb diversity. However, although constituting an essential and ecologically highly diverse part of modern ecosystems, squamate reptiles remain yet poorly studied in limb evo-devo, especially with respect to basal taxa.In the proposed research project, the gekkotan Hemidactylus will be developed as a new non-traditional model organism and provides the basis for a detailed study of the developmental patterning of the limbs by means of gene expression. Hemidactylus is ideally suited for studying molecular limb development, on the one hand due to its basal squamate position, on the other hand because it displays a breadth of morphological modifications related to ecological specialisation in its autopods, including size reduction in phalangeal elements, presence of adhesive toepads and paraphalanges.An existing successful captive breeding colony of Hemidactylus produces fresh embryonic tissue needed. A normal table of development, documenting early and late pattern formation of the limbs, will be produced via histological staining and microCT scans, describing the development of morphological modifications in Hemidactylus autopods and comparing it to other squamates. Further, it provides a fundamental basis for concurrent gene expression analyses. The temporal and spatial expression patterns of nine candidate genes known to be involved in limb development in the traditional model organisms mouse and chicken, will be studied via in situ hybridisation on histological serial sections. Results will be compared to the ones obtained from the closely related Madagascar ground gecko Paroedura picta and the lacertid, endemic to the Canary islands Gallotia galloti, and will contribute key data to broaden our understanding of limb developmental trajectories in the squamate limb.

• DFG Programme: Research Grants