How fish got the strength to walk
Cole NJ, Hall TE, Don EK, Berger S, Boisvert CA, Neyt C, Ericsson R, Joss J, Gurevich DB, Currie PD.
Development and evolution of the muscles of the pelvic fin. PLoS Biol. 2011 Oct;9(10):e1001168.
Briefly tell us a bit about yourself, your career path over the years, and specifically what brought you to begin working on muscle development and its evolution in the limb.
How do you classify critical junctures in vertebrate phylogeny? What specific developmental characteristics led you to choose the 5 fish species that you did as representatives of muscle formation for the all fish?
Can you please compare and contrast what is known about the molecular signaling pathways regulating myotomal extension versus myoblast migration into the limb? What genes, including lbx, are known to be required for this myotomal extension or myoblast migration and are any similarly required between the two processes of limb muscle development?
You note how epithelial myotomal extension occurred during pelvic muscle formation in the two chondricthyan species (chimera and bamboo shark), but no lbx1 was expressed in the epithelial buds, suggesting that the epithelial bud myoblasts do not undergo EMT and their model for pelvic muscle formation is primitive. Do you think the myoblasts of the bamboo shark and chimera, being more basal in the vertebrate phylogeny, may utilize an altogether different transcription factor in the epithelial to mesenchymal transition (not lbx1)? To test this hypothesis, would you test for mesenchymal character of the epithelial bud tip cells by a method other than lbx1 labeling?
The somite transplantation technique you created and utilized sounds really amazing. What was the process like trying to perfect this method, and were there any morphological deformations that occurred because of potential trauma due to the somite transplant?
You state that the fully derived mode of appendicular formation would allow the pectoral and pelvic fins to develop in a synchronous manner that is not seen in the primitive mode of appendicular formation. Why is this timing of development important for tetrapod species but not in cartilaginous fish species?
I was wondering about your hypotheses regarding fin development in the transition states between the chondrichthyan species and the bony fish you examined. As you hypothesize that the bimodal state of pelvic fin development is an intermediate form, do you suppose that pectoral fins went through an intermediate bimodal form before arriving at the derived state?
Followup: If so, do suppose that the bimodal form evolved in both pectoral and pelvic fins simultaneously or consecutively? In the paper, you mention that the derived form results in fin positioning plasticity (Cole et al. 7), which I imagine would be very evolutionarily beneficial. As such, can you hypothesize why only pectoral fins display the derived form? (This obviously excludes tetrapods.) Can you hypothesize any selection pressures that would drive this result?
Pelvic girdle in early tetrapod (Acanthostega) compared to sarcopterygian fish (Eusthenopteron) is considerably larger. It has been proposed that the adoption of the “fully derived mode of appendicular muscle formation” will facilitate “the dorsal shift of the pelvic girdle location”. Is this derived mode also related to the size of the pelvic girdle?
Are there any studies comparing muscle development in the fins of whales and fish? Because whales evolved from tetrapods and therefore may have the more derived form of limb/fin muscle development, I think it would be interesting to explore the different mechanisms as evidence of convergent evolution.
I understand that fish are your research model, but frogs are an interesting representation of the transformation from fish to tetrapod. Do you think comparisons of the development of amphibian limb musculature in the larva and during metamorphosis to the developmental process you describe in zebrafish could reveal any evolutionary insights? How does the bimodel character model play out in tadpoles and frogs?
Currently in your opinion what are the most pressing questions about the development and evolution of muscle in the tetrapod limb, and what steps is your lab taking to address these questions?