Related Experiment Videos
The origin and evolution of animal appendages
G Panganiban1, S M Irvine, C Lowe
1Department of Anatomy, University of Wisconsin, 1300 University Avenue, Madison, WI 53706, USA.
Summary
The Distal-less (Dll) gene is expressed in diverse animal appendages, suggesting its ancient role in patterning body outgrowths. This regulatory gene likely originated in a common ancestor, aiding appendage evolution across many species.
Area of Science:
- Developmental Biology
- Evolutionary Biology
- Genetics
Background:
- Appendages are crucial for animal survival, with their genetic basis studied mainly in insects and vertebrates.
- The Distal-less (Dll) homeoprotein is key in insect limb outgrowth, and its orthologs (Dlx) are in vertebrate limb/fin development.
Purpose of the Study:
- To investigate if Distal-less (Dll) gene expression is a conserved mechanism for appendage formation across diverse animal phyla.
- To explore the evolutionary origins of appendage patterning genes.
Main Methods:
- Comparative gene expression analysis of Distal-less (Dll) and its orthologs (Dlx).
- Examination of Dll/Dlx expression patterns in developing appendages of annelids, onychophorans, ascidians, and echinoderms.
Main Results:
- Dll expression was observed along the proximodistal axis in developing parapodia (annelids), lobopodia (onychophorans), ampullae (ascidians), and tube feet (echinoderms).
- This conserved expression pattern across six coelomate phyla suggests a shared ancestral origin rather than multiple independent gene co-options.
Conclusions:
- Ectodermal Dll/Dlx expression along proximodistal axes likely originated once in a common ancestor.
- This ancestral genetic machinery was subsequently utilized for patterning various body wall outgrowths, including appendages, in early bilaterians.