Tue 15 Jul 2014
By Laurel Hamers
Our arms and legs normally work so fluidly that we may forget that their size and location were determined by complex genetic control during early development.
Keys to the precise regulatory ballet that makes our limbs look the way they do may be found in a seemingly dissimilar group of organisms: sharks and skates.
Cartilaginous fish like sharks and skates are the oldest fish to have pectoral fins: paired appendages that are the evolutionary predecessor of our arms. Tetsuya Nakamura, a postdoctoral researcher at the University of Chicago, is spending the summer at the MBL investigating these cartilaginous fish. He hopes to elucidate the molecular mechanisms responsible for the diversity of fin shapes in this single group of fish and, on a broader scale, the evolution of appendage shapes across species.
“The best way to understand the diversity of fin types is to study an extremely strange fish, like the skate,” says Nakamura. “The pectoral fins of skate are very wide—they’re totally different from other animals.”
Nakamura is focusing on Hox genes, which control body patterning during embryonic development; they are responsible, for example, for making sure your arms attach below your shoulders and not out the top of your head. Researchers can manipulate individual Hox genes and readily see structural differences in the body parts influenced by that gene.
By comparing expression patterns of Hox genes in the fins of skates and closely related sharks, Nakamura is identifying specific genes that may be responsible for the skate’s elongated pectoral fins compared to the shark’s narrower ones. He will then manipulate the expression of these genes in an attempt to alter fin shape.
“My opinion is that fin width is very important in deciding fin shape,” he says. “If I can control fin width, for example, to make narrower fin bases in skate, I think their fin shape would be like a shark’s.”
Nakamura, who is spending his first summer at MBL, is a member of Neil Shubin’s lab in the Department of Organismal Biology and Anatomy at UChicago.