Oxidative stress, photodamage and the role of screening pigments in insect eyes

Abstract

SUMMARYUsing red-eyed mutant triatomine bugs (Hemiptera: Reduvidae), we tested the hypothesis of an alternative function of insect screening pigments against oxidative stress. To test our hypothesis, we studied the morphological and physiological changes associated with the mutation. We found that wild-type eyes possess a great amount of brown and red screening pigment inside the primary and secondary pigment cells as well as in the retinular cells. Red-eyed mutants, however, have only scarce red granules inside the pigmentary cells. We then compared the visual sensitivity of red-eyed mutants and wild types by measuring the photonegative responses of insects reared in light:dark cycles [12h:12h light:dark (LD)] or constant darkness (DD). Finally, we analyzed both the impact of oxidative stress associated with blood ingestion and photodamage of UV light on the eye retina. We found that red-eyed mutants reared in DD conditions were the most sensitive to the light intensities tested. Retinae of LDreared mutants were gradually damaged over the life cycle, while for DD-reared insects retinae were conserved intact. No retinal damage was observed in non-fed mutants exposed to UV light for 2weeks, whereas insects fed on blood prior to UV exposure showed clear signs of retinal damage. Wild-type insects exposed to UV light showed a marked increase in the amount and density of screening pigments.

Increasing the illumination slowly over several weeks protects against light damage in the eyes of the crustacean Mysis relicta

“…Faster cycling might be linked to changes in the amount or composition of proximal screening pigments or intrinsic properties of the membrane. Some screening pigments have photoprotective activity (Abu Khamidakh et al, 2010;Insausti et al, 2013) and membrane properties are universally regulated by changing lipid composition (see below). It may further be noted that polyunsaturated fatty acids formed as part of the phototransduction reactions have been shown to enhance excitation in Drosophila (Chyb et al, 1999).…”

“…Light absorption and phototransduction are associated with the release of large amounts of energy liable to cause damage through oxidative stress and several other possible mechanisms (Glickman, 2002;Organisciak and Vaughan, 2010;Insausti et al, 2013). The threat of light damage to eyes is universal and especially acute when eyes tuned for exquisite sensitivity are exposed to bright light.…”

Ommochromes in invertebrates: biochemistry and cell biology

“…The chemical properties of chromophores often make them suitable for transporting electrons or reacting with oxidants, reducers and free radicals, as well as functioning in vision (Needham, ). All these functions have been proposed to be fulfilled by ommochromes in nature (Needham, ; Stavenga, ; Insausti, Le Gall & Lazzari, ; Romero & Martínez, ), often without direct proof. Furthermore, protostomes generally lack the glutarate and nicotinamide biosynthesis pathway that catabolises the amino acid tryptophan (Linzen, ).…”

Pigmentation loci as markers for genome editing in the Chagas disease vector Rhodnius prolixus

“…In D. melanogaster [26] and Tribolium castaneum [27] w, scarlet (st) and brown (bw) loci encode ABC transporters that for heteromeric channels: proteins encoded by bw and w transport the red pteridines into cells of developing eyes, while w plus st transport brown ommochrome pigments. Eye color mutations affecting components of either pathway have been described in several insect orders [9,[27][28][29][30][31][32][33][34].…”