Mosquito ommochrome eye pigment biosynthesis is understood, except the terminal step involving 3-hydroxykynurinine (3HK) oxidation to xanthommatin. This step can proceed enzymatically or non-enzymatically, but relative contributions of these pathways are unclear. We isolated an ommochrome-deficient Culex pipiens mutant (crimson), which may serve as a model to address this question and as a marker for transgenesis studies. Addition of xanthommatin precursors to rearing water did not rescue wild-type phenotype, indicating that the mutation affects the terminal step of ommochrome biosynthesis. Crosses indicated that crimson is sex-linked and fully recessive. Crimson-homozygous embryos exhibit no eyespot; first-instar larval ocelli are colorless. Eyes progress from yellow to red through immature development. Teneral adults possess red eyes, darkening to wild-type 5 days post-emergence. Thin-layer chromatography demonstrated teneral crimson adults lacked ommochrome pigments. Wild-type and aged crimson adults had different ommochrome profiles but individual ommochromes could not be resolved. Spectrophotometric analysis of eye extracts indicated teneral crimson adults lacked xanthommatin in eye tissues, but had abnormally high levels of 3HK. Extracts of 10-day old adults had depleted levels of 3HK, but exhibited ommochrome production. Evidence indicates 3HK is transported into mutant eyes prior to adult emergence but is not enzymatically oxidized to xanthommatin, resulting in 3HK hyper-accumulation. Ommochromes are formed by non-enzymatic 3HK oxidation after emergence, but mutant ommochrome profiles differ from wild-type. Ommochrome differences may reflect differing redox environments in mutant eyes vs. wild-type. Our data indicate that terminal ommochrome biosynthesis can proceed enzymatically or non-enzymatically in vivo.
Species 1: Diptera Culicidae Culex pipiens (Northern House Mosquito)
Keywords: Ommochrome, mutant
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