Crimson: a novel sex-linked eye color mutant of Culex pipiens L. (Diptera: Culicidae).
Xanthommatin is the primary ommochrome eye pigment in mosquitoes. The terminal step in xanthommatin biosynthesis, involving oxidation of 3-hydroxykynurenine (3HK), can proceed enzymatically by phenoxazinone synthase or by nonenzymatic auto-oxidation of 3HK. The relative contributions of these pathways, however, are unclear. We isolated a novel Culex pipiens mutant (crimson) that could be used to address this question. Homozygous crimson embryos exhibit no visible eyespot; first-instar larval ocelli are colorless. Eyes gradually turn red through immature development. Teneral crimson adults possess red eyes that darken to wild-type approximately 5 d after emergence. Crosses indicate that crimson is sex-linked and fully recessive. Addition of xanthommatin precursors to rearing water did not rescue wild-type phenotype and suggested that the mutation is in the terminal step of ommochrome biosynthesis. Crimson expression was not temperature sensitive. Thin-layer chromatography demonstrated teneral crimson adults lacked xanthommatin. Teneral and aged wild-type adults exhibited low-mobility black ommochrome spots; aged crimson adults exhibited low-mobility brown-red ommochrome spots. Absorbance spectroscopy of eye extracts indicated teneral adult crimson eyes lacked xanthommatin but had abnormally high levels of 3HK, whereas extracts of 10-d-old crimson adults had depleted levels of 3HK and detectable levels of xanthommatin. Light microscopy indicated that eyes of young (3 d old) wild-type adults had a high concentration of pigment granules. Eyes of teneral crimson adults had no pigment granules. Eyes of 20-d-old crimson adults had low levels of pigment granules. We suggest two possible mechanisms for the crimson mutation: (1) transport of 3HK into the pigment cells and/or pigment granules is slow, with normal oxidation of 3HK into xanthommatin, or (2) 3HK is transported normally into pigment cells/granules but is not immediately oxidized to xanthommatin, resulting in 3HK hyper-accumulation and slow nonenzymatic production of xanthommatin after adult emergence.
Rasgon
Jason L
JL
Department of Entomology, North Carolina State University, Raleigh, NC 27695, USA.
Scott
Thomas W
TW
D000375:Aging; D000818:Animals; D003433:Crosses, Genetic; D003465:Culex / Q000235:genetics*; D005123:Eye / Q000166:cytology; D005127:Eye Color / Q000235:genetics*; D005260:Female; D006720:Homozygote; D008297:Male; D009154:Mutation; D010641:Phenotype; D014366:Tryptophan Oxygenase / Q000235:genetics
D014366:Tryptophan Oxygenase