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Developing an ancient epithelial appendage: FGF signalling regulates early tail denticle formation in sharks
Rory L Cooper1, Kyle J Martin1, Liam J Rasch1
1Department of Animal and Plant Sciences, and the Bateson Centre, University of Sheffield, Sheffield, S10 2TN UK.
Evodevo
|May 5, 2017
Summary
The study shows that shark dermal denticles (placoid scales) develop using a conserved gene network, suggesting homology with amniote skin appendages like feathers and hair. This indicates a 450-million-year-old shared evolutionary origin for vertebrate integumentary organs.
Area of Science:
- Developmental Biology
- Evolutionary Biology
- Comparative Genomics
Background:
- Vertebrate integumentary organs (scales, feathers, hair) develop from epithelial placodes.
- Homology of placode development in amniotes is established, but less is known in basal vertebrates.
- Shark dermal denticles (odontodes) are ancient integumentary appendages.
Purpose of the Study:
- To test the homology of shark dermal denticles with amniote integumentary organs.
- To investigate the conservation of gene regulatory networks (GRNs) in placode development.
- To examine the role of fibroblast growth factor (FGF) signaling in shark denticle formation.
Main Methods:
- Used the shark *Scyliorhinus canicula* as a model organism.
- Analyzed expression of conserved developmental genes (FGFs, *shh*, *bmp4*).
- Inhibited FGF signaling using small molecules during caudal denticle development.
Main Results:
- Shark denticle placodes express conserved amniote placode GRN genes (FGFs, *shh*, *bmp4*).
- Denticle placodes exhibit characteristics of amniote skin appendage development, including reduced proliferation.
- FGF signaling inhibition disrupted placode development and downregulated *shh* and *bmp4* expression.
Conclusions:
- The core GRN for vertebrate integumentary appendages is highly conserved over 450 million years.
- Provides evidence for the evolutionary homology of epithelial placodes across jawed vertebrates.
- Epithelial placodes represent a foundational developmental unit for diverse vertebrate skin structures.
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