The tiny zebrafish also has the ability to regenerate parts that humans can’t that could provide important clues for regenerative medicine, Dr. John E. Dowling said.
Dowling was the keynote speaker at the fourth annual Georgia Health Sciences University Vision Discovery Institute Scientific Retreat. He is the Gordon and Llura Gund Professor of Neuroscience, Ophthalmology, and Molecular and Cellular Biology at Harvard.
He turned to the versatile zebrafish in the early 1990s, around the time when the fish were gaining attention as a research vehicle for their ability to reproduce quickly and cheaply, as a way to study development, mutations and the genetics of vision.
In some of Dowling’s current work, for instance, one mutant model of zebrafish appeared to be completely blind in standard tests yet physically normal.
Further examination found a distinct defect in a visual system called ON that senses light increasing but not in a visual system called OFF that senses light decreasing, which appeared to be responding normally.
“That brought us to the conclusion that maybe it is the ON pathway you need to see movement,” Dowling said.
Zebrafish possess an abundant amount of cones in the eye, more than humans, that correspond to four color categories – red, green, blue and ultraviolet, Dowling said. Most mammals can sense only two and humans get only three: red, green and blue.
“They have a richer color vision system than we do,” Dowling said.
For instance, zebrafish have some color-sensing cells in the retina that in primates and humans are found back in the brain in the cortex, which would make those cells easier to study in zebrafish, he said.
Citing questions raised by Dr. Jeffrey Mumm at GHSU, Dowling said more work should focus on the ability of zebrafish to regenerate body parts that humans cannot, such as the whole retina in the eye.