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Identification and Distribution of Dietary Precursors of The View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Vision Research 39 (1999) 219–229 Identification and distribution of dietary precursors of the Drosophila visual pigment chromophore: analysis of carotenoids in wild type and ninaD mutants by HPLC David R. Giovannucci *, Robert S. Stephenson Department of Biological Sciences, Wayne State Uni6ersity, Detroit, MI 48202, USA Received 3 July 1997; received in revised form 10 November 1997 Abstract A dietary source of retinoid or carotenoid has been shown to be necessary for the biosynthesis of functional visual pigment in flies. In the present study, the larvae or adults of Drosophila melanogaster were administered specific carotenoid-containing diets and high performance liquid chromatography was used to identify and quantify the carotenoids in extracts of wild type and ninaD visual mutant flies. When b-carotene was fed to larvae, wild type flies were shown to hydroxylate this molecule and to accumulate zeaxanthin and a small amount of b-cryptoxanthin. Zeaxanthin content was found to increase throughout development and was a major carotenoid peak detected in the adult fly. Carotenoids were twice as effective at mediating zeaxanthin accumulation when provided to larvae versus adults. In the ninaD mutant, zeaxanthin content was shown to be specifically and significantly altered compared to wild type, and was ineffective at mediating visual pigment synthesis when provided to both larval and adult mutant flies. It is proposed that zeaxanthin is the larval storage form for subsequent visual pigment chromophore biosynthesis during pupation, that zeaxanthin or b-crytoxanthin is the immediate precursor for light-independent chromophore synthesis in the adult, and that the ninaD mutant is defective in this pathway. © 1998 Elsevier Science Ltd. All rights reserved. 1. Introduction dietary source for the generation of rhodopsin in flies (Zimmerman & Goldsmith, 1971; Harris, Ready, Lip- The identification of 11-cis 3-hydroxyretinal as the son, Huspeth & Stark, 1977; Stephenson, O’Tousa, visual pigment chromophore in Calliphora (Vogt, 1983; Scarvarda, Randall & Pak, 1983; Sapp, Christianson, Vogt & Kirschfeld, 1984) and in Drosophila (Gold- Maier, Studer & Stark, 1991). smith, Marks & Bernard, 1986; Seki, Fujishita, Ito, Since Vogt’s (1983, 1984) discovery that the fly’s Matsuoka & Tsukida, 1986; Tanimura, Isono & Tsuka- retinal chromophore is 3-hydroxylated, it has been pro- hara, 1986; Giovannucci & Stephenson, 1987), and the posed (and shown definitively in Calliphora) that flies elucidation of its recycling in the dipteran retina have the ability to convert a- and b-carotene to lutein (Schwemer, 1988) has aroused interest in the uptake, and zeaxanthin, respectively (Vogt & Kirschfeld, 1984), transport, and conversion of the carotenoid precursors and to use these polar derivatives to produce functional required for the biosynthesis of this novel chromophore visual pigment (Stark, Schilly, Christianson, Bone & and visual pigment. All higher animals studied to date, Landrum, 1990) or photoprotective pigment (Zhu & including flies, lack the ability to synthesize carotenoids Kirschfeld, 1984). or retinoids de novo and, thus, must obtain them To generate 11-cis 3-hydroxyretinal directly from b- through their diet (Kayser, 1982). An extensive body of carotene, a fly must perform at least three important b literature has established that -carotene can serve as a structural modifications on the carotene molecule: (1) hydroxylation at the 3 or 3% position of the ionone ring; (2) isomerization of the hydrocarbon chain at the 11 or * Corresponding author. Present address: Department of Physiol- 11% position; and (3) cleavage to a C20 molecule. How- ogy, University of Michigan Medical School, Ann Arbor, MI 48109, USA. Tel.: +1 313 7643339; fax: +1 313 9368813; e-mail: lud- ever, the exact sequence of these manipulations is not [email protected]. known. Zeaxanthin and lutein have been shown to be 0042-6989/98/$ - see front matter © 1998 Elsevier Science Ltd. All rights reserved. PII: S0042-6989(98)00184-9 220 D.R. Gio6annucci, R.S. Stephenson / Vision Research 39 (1999) 219–229 sufficient for the formation of functional rhodopsin in Table 1 Drosophila (Stark, Schilly, Christianson, Bone & Lan- Fly growth medium composition drum, 1990). Therefore, these hydroxylated, principally Sucrose-agar medium Cornmeal-agar medium all-trans carotenoids may function as substrates for the (g/lH2O) (g/lH2O) synthesis of the chromophore via a light-independent pathway, as demonstrated by the accumulation of 11- Agar19.8 68 cis 3-hydroxretinal in the heads of Drosophila reared on Yeast 126.4 193 xanthophylls (oxidized C40 compounds including hy- Sugar54 376 Proprionic acid11 ml 40 ml droxylated carotenoids) and maintained in the dark Yellow corn-0 773 (Seki, Fujishita, Ito, Matsuoka & Tsukida, 1986; Isono, meal Tanimura, Oda & Tsukahara, 1988). This would provide an alternative pathway to the adult fly’s blue light-dependent isomerization of all-trans retinal to the 2. Materials and methods 11-cis form (Schwemer, 1984; Isono, Tanimura, Oda & Tsukahara, 1988). However, the identification, quantifi- 2.1. Flies cation, and distribution of specific carotenoid subtypes (the presumed dietary sources for this unusual chro- Wild type and ninaD mutants (P246 and TH382 mophore) in Drosophila remain largely uncharacterized. The use of mutants that are defective in chromophore alleles) of Drosophila melanogaster were of the Oregon- biosynthesis will likely aid in determining the physio- R strain. The mutants were provided by Dr William logically important dietary substrates. Pak and Dr Theodore Homyk, Jr. of Purdue Univer- The Drosophila visual mutants designated ninaA sity. Both ‘wild type’ and mutant flies carried the through ninaH are characterized by reduced rhodopsin mutation (w) and therefore lacked screening pigment in levels and defective electroretinograms, indicating that the eye. a reduction in the amount of photopigment can occur through a variety of pathways (Pak, 1995). For exam- 2.2. Carotenoid-enriched and carotenoid-free diets ple, the 11-cis isomer of retinal or 3-hydroxyretinal has been shown to be necessary for the expression of func- The flies were reared on cornmeal-agar medium (the tional rhodopsin in flies (Schwemer, 1984; Isono, Tan- standard fly growth medium) or sucrose-agar medium imura, Oda & Tsukahara, 1988), and opsins with (Sang, 1956) (see Table 1). The former contains zeaxan- specific amino acid deletions or substitutions that result thin (Table 2), whereas the latter was free of in defective 11-cis retinal binding show altered cellular carotenoids or retinoids (data not shown) and was in processing and protein trafficking (Doi, Molday & some cases supplemented with pure carotenoid (100– Khorana, 1990; Anukanth & Khorana, 1994; Ridge, 500 mg/ml). b-carotene (Fluka), xanthophyll extract Lee & Abdulaev, 1996). Recently, evidence for altered (ICN), zeaxanthin, b-cryptoxanthin (gifts from Hoff- opsin processing has been demonstrated in ninaD flies mann-LaRoche), apo-8 b-carotenal (Fluka), or can- (Colley, Baker, Stamnes & Zuker, 1991; Ozaki, Na- thaxanthin (Fluka) was dispersed in sucrose-agar gatani, Ozaki & Tokunaga, 1993). Thus, genetic lesions medium that was warmed to a liquid. In general, flies that interfere with the availability of this isomer are were raised on a 12/12 h light/dark protocol at 22– likely to have profound effects on rhodopsin levels and 24°C or, in some cases, in complete darkness. Under on the function of the fly photoreceptor. Previously, we these conditions, the dispersed b-carotene had a half- have shown that the ninaD visual mutant expresses low life greater than 4 days at 22°C as determined by levels of rhodopsin when grown on standard (cornmeal- HPLC. In earlier experiments, flies were raised on agar) fly medium, but could be rescued (restored to the yellow cornmeal extract-enriched or carrot juice-en- wild type phenotype) by feeding with high levels of riched sucrose medium which contained substantial b-carotene or all-trans retinoids (Stephenson, O’Tousa, amounts of xanthophylls, carotenoid isomers, and Scarvarda, Randall & Pak, 1983; Giovannucci & other unidentified carotenoids. For the direct demon- Stephenson, 1988). This suggested that the ninaD mu- tant was deficient in some aspect of retinoid or Table 2 carotenoid metabolism, although the precise defect was Carotenoid content of cornmeal-agar medium (n=3) not determined. In the present study, high performance liquid chromatography (HPLC) was used to identify pmol/mg dry weight and quantitate the content and the distribution of 9 potential dietary carotenoid precursors of the fly visual Zeaxanthin 229 18 Lutein 91911 pigment chromophore in extracts of both wild type b-Cryptoxanthin 5397 Drosophila and ninaD larvae and adult flies fed on b-Carotene 43925 specific diets. D.R. Gio6annucci, R.S. Stephenson / Vision Research 39 (1999) 219–229 221 Table 3 Fly heads and bodies were separated by vortexing with Key for fly dietary history notation liquid nitrogen and shaking over a c30 mesh sieve. symbol Tissue was dried by blotting on filter paper, weighed, glass homogenized, and extracted twice with hexane/ Genotype acetone 1:1. If the tissue was not immediately used, it Wild type wt was sealed and stored at −70°C. For the analysis of P246 NinaD P246 carotenoids in fly culture media, a portion of medium NinaDTH382 TH382 was ground with two volumes of anhydrous Na2SO4 Stage and extracted with methylene chloride. B\ Larva 2.5. Chromatography Pupa () Adult (imago) {} Carotenoids and xanthophylls were reverse-phase Diet Carotenoid-free sucrose-agar medium (SAM) — chromatographed by the method of Nells & DeLeen- Cornmeal-agar medium cm heer (1983). Extracts were dried (Savant Speed-Vac) Carrot juice+SAM cj and the residue dissolved in 20-100 ml of mobile phase. b-carotene+SAM b-car Samples were injected onto a Zorbax-ODS column b b -cryptoxanthin+SAM -cry (Dupont) and eluted with 20% methylene chloride in Zeaxanthin+SAM Zea acetonitrile (v/v) at a flow rate of 1 ml/min. Absorbance For example, wt: Bb-car\(){–}, means a wild-type fly raised from was monitored at 450 nm.
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