This week there are a few really interesting papers in Cell that are about various key questions/themes in evolution. My favorite is about fins and limbs: the authors found a genetic “cassette” in fish genomes (zebrafish is their experimental system) that can be activated to induce the formation of bones that are normally associated with limb development. Two things jump out as especially interesting to me about the discovery:
- The signaling system they describe was not previously known to be involved in limb development. The authors show that it is in fact part of limb development in mice. And it was discovered in fish! Wild.
- The extra bones that develop in the activated mutants are strikingly normal; quoting the abstract, they “integrate into musculature, form joints, and articulate with neighboring elements.”
The graphical abstract is a nice way to explore what they found:
And here is the regular abstract:
Changes in appendage structure underlie key transitions in vertebrate evolution. Addition of skeletal elements along the proximal-distal axis facilitated critical transformations, including the fin-to-limb transition that permitted generation of diverse modes of locomotion. Here, we identify zebrafish mutants that form supernumerary long bones in their pectoral fins. These new bones integrate into musculature, form joints, and articulate with neighboring elements. This phenotype is caused by activating mutations in previously unrecognized regulators of appendage patterning, vav2 and waslb, that function in a common pathway. This pathway is required for appendage development across vertebrates, and loss of Wasl in mice causes defects similar to those seen in murine Hox mutants. Concordantly, formation of supernumerary bones requires Hox11 function, and mutations in the vav2/wasl pathway drive enhanced expression of hoxa11b, indicating developmental homology with the forearm. Our findings reveal a latent, limb-like pattern ability in fins that is activated by simple genetic perturbation.
In the same new batch of papers in Cell there is a paper on overall genetic factors in fish-to-land evolution, gleaned from a new set of genomes from ray-finned fish, and a paper describing primate-specific 3D genome features that may explain primate- and human-specific aspects of the cerebral cortex.
PDFs sent happily on request. I have only read the fin/limb paper and haven’t yet explored the other two.