Fatty acid composition of Drosophila photoreceptor light-sensitive microvilli

Abstract

Phototransduction, the mechanism underlying the electrical response to light in photoreceptor cells, has been thoroughly investigated in Drosophila melanogaster, an essential model in signal transduction research. These cells present a highly specialized photosensitive membrane consisting of thousands of microvilli forming a prominent structure termed a rhabdomere. These microvilli encompass the phototransduction proteins, most of which are transmembrane and exclusively rhabdomeric. Rhabdomere membrane lipids play a crucial role in the activation of the transient receptor potential ionic channels (TRP and TRPL) responsible for initiating the photoresponse. Despite its importance, rhabdomere lipid composition has not been established. We developed a novel preparation enriched in rhabdomere membranes to perform a thorough characterization of the lipidomics of Drosophila rhabdomeres. Isolated eyes (500) were homogenized and subjected to a diff erential centrifugation protocol that generates a fraction enriched in rhabdomere membrane. Lipids extracted from this preparation were identifi ed and quantifi ed by gas chromatography coupled to mass spectrometry. We found an abundance of low sterol esters (C16:0, C18:0), highly abundant and diverse triglycerides, free fatty acids, a moderate variety of mono and diacyglycerols (C:16:0, 18:0, C18:1) and abundant phospholipids (principally C18:2). This preparation opens a new avenue for investigating essential aspects of phototransduction.

Lipidome Unsaturation Affects the Morphology and Proteome of the Drosophila Eye

“…We conclude that the dietary supply of TAGs with medium-chain saturated fatty acid moieties, which are compositionally similar to common TAGs in Drosophila , 3 , 19 neither impacts the eye morphology nor the content of major lipid classes in the eye. However, these supplemented TAGs affected several metabolic pathways and decreased the molar abundance of major phototransduction proteins.…”

“…Since both phototransduction and morphology-related proteins were quantified in the same experiment, this indicates that the same rate of decrease in the abundance of the former proteins was not because of normalization or sample processing errors. We conclude that the dietary supply of TAGs with mediumchain saturated fatty acid moieties, which are compositionally similar to common TAGs in Drosophila, 3,19 neither impacts the eye morphology nor the content of major lipid classes in the eye. However, these supplemented TAGs affected several metabolic pathways and decreased the molar abundance of major phototransduction proteins.…”

“…Consistent with this dietary similarity, medium-chain saturated TAGs are common in D. melanogaster . 3 , 19 In contrast, M2-food supplied unsaturated fatty acids that flies cannot generate de novo but that can be metabolically derived from C22:6. 4 In both M2- and M3- foods, the relative (w/w) content of the TAGs was the same.…”

“…Drosophila lacks the ability to synthesize long-chain PUFAs from shorter-chain precursors (such as linoleic acid, C18:2), and the rhabdomere membranes lack lipids with PUFA moieties of more than 18 carbon atoms. 4 , 19 The TAG that we added in the case of M2 food supplied the omega-3 PUFA DHA, which has not been detected in Drosophila ( 4 , 49 ) but is present at high levels in the rhabdomere-equivalent outer segments of mammalian photoreceptors. 50 − 52 Unexpectedly, we discovered that once the supplied DHA was metabolized to various shorter-chain polyunsaturated GPLs, the lipid class composition of the eye remained unchanged.…”

Hydroxylated sphingolipid biosynthesis regulates photoreceptor apical domain morphogenesis

“…Despite the fact that a huge amount of membrane is required to generate the rhabdomere, information about the role of lipids in this process are lacking. So far, studies on lipids in the fly eye have concentrated on their role in phototransduction mostly in mature PRCs ( Muñoz et al, 2013 ; Raghu et al, 2009 ; Randall et al, 2015 ), but how rhabdomere morphogenesis is coupled to lipids and their metabolism has not been addressed.…”