Understanding Fish Fins

One of the great transformations required for the descendants of fish to become creatures that could walk on land was the replacement of long, elegant fin rays by fingers and toes. In the Aug. 17, 2016 issue of Nature, scientists from the University of Chicago show that the same cells that make fin rays in fish play a central role in forming the fingers and toes of four-legged creatures.

After three years of painstaking experiments using novel gene-editing techniques and sensitive fate mapping to label and track developing cells in fish, the researchers describe how the small flexible bones found at the ends of fins are related to fingers and toes, which are more suitable for life on land.

"When I first saw these results you could have knocked me over with a feather," said the study's senior author, Neil Shubin, PhD, the Robert R. Bensley Distinguished Service Professor of Organismal Biology and Anatomy at the University of Chicago. Shubin is an authority on the transition from fins to limbs.

"For years," he said, "scientists have thought that fin rays were completely unrelated to fingers and toes, utterly dissimilar because one kind of bone is initially formed out of cartilage and the other is formed in simple connective tissue. Our results change that whole idea. We now have a lot of things to rethink."

To unravel how fins might have transformed into wrists and fingers, the researchers worked mostly with a standard fish model: the zebrafish.

Tetsuya Nakamura, PhD, a postdoctoral scholar in Shubin's lab, used a gene-editing technique, CRISPR/Cas, in zebrafish to delete important genes linked to limb-building, and then selectively bred zebrafish with multiple targeted deletions. He spent more than two years building and cross breeding the fish mutants, a project that began at the Marine Biological Laboratories in Woods Hole, Massachusetts.