A NEW FORM OF INHERITED RED-BLINDNESS IDENTIFIED IN ZEBRAFISH

A red-blind zebrafish mutant, partial optokinetic response b (pob), ha s been isolated by measuring eye movements of larvae in a three-genera tion screen for recessive mutations affecting the visual system. pob l arvae exhibit eye movements in response to rotating black and white st ripes illuminated with white light, but they do not move their eyes wh en the stripes are illuminated with red light. Physiological, immunohi stochemical, and in situ hybridization analyses of pob retinas showed a selective loss of red-sensitive cones at 5 days postfertilization (d pf). At 3 dpf, cells expressing red opsin are present, suggesting that red-sensitive cones form initially but then disappear rapidly, wherea s other photoreceptors remain, Linkage analysis indicated that the mut ation identified in the pob mutant is not at the red opsin locus, Beca use red opsin is the only known molecule unique to red cones, these da ta suggest that a novel gene is required for the maintenance or functi on of red cones.