Contrary to a long-held belief, zebrafish larvae can see with their rod photoreceptors
Zebrafish develop their eyes rapidly. In just three days, zebrafish eyes form all major classes of retinal neurons including rod photoreceptors and the young larvae begin to see. Their rods, however, were deemed immature and not functional until two to three weeks by early studies. This notion has limited the utility of larval zebrafish to study rod function and disease for more than 20 years.
This long-standing notion has recently been revisited by Leung lab. They developed tests to study vision of young zebrafish larvae under very dim light that only rods could respond. They then used the test to study a mutant that lacked functional cones but still possessed functional rods. They found that 6-day-old larvae of the mutant could sense dim-light change and track moving objects under very dark environment. Their results show that zebrafish larvae can see with their rods at a much younger stage than previously thought.
Leung lab members who contributed to this study include Prahatha Venkatraman, a Schlumberger Foundation Graduate Fellow; Menna Hassan, a West Lafayette Jr./Sr. High School student; and Yuk Fai Leung. Their study was published in the October issue of Investigative Ophthalmology and Visual Science, a leading eye-research journal.
This discovery will make zebrafish an even better model for studying rod-degenerative diseases, including retinitis pigmentosa. Using their unique dim-light tests, Leung lab students have been screening drugs on zebrafish larvae with rod degeneration. They have identified drug candidates that improve rod response and preserve dying rods in these rod-degeneration larvae. These drugs may ultimately become new treatments for patients who suffered from rod degeneration.
Venkatraman P, Mills-Henry I, Padmanabhan KR, Pascuzzi P, Hassan M, Zhang J, Zhang X, Ma P, Pang CP, Dowling JE, Zhang M, Leung YF. Rods contribute to visual behaviour in larval zebrafish. Invest Ophthalmol Vis Sci. 2020;61(12):11.