No abstract

polyunsaturated fatty acids (pUfAs) play crucial roles in adaptation to cold environments in a wide variety of animals and plants. However, the mechanisms by which PUFAs affect thermoregulatory behaviour remain elusive. Thus, we investigated the roles of PUFAs in thermoregulatory behaviour of Drosophila melanogaster. To this end, we generated transgenic flies expressing Caenorhabditis elegans Δ12 fatty acid desaturase (FAT-2), which converts mono-unsaturated fatty acids to PUFAs such as linoleic acid [C18:2 (n-6)] and linolenic acid [C18:3 (n-3)]. Neuron-specific expression of FAT-2 using the GAL4/UAS expression system led to increased contents of C18:2 (n-6)-containing phospholipids in central nerve system (CNS) and caused significant decreases in preferred temperature of third instar larvae. In genetic screening and calcium imaging analyses of thermoreceptor-expressing neurons, we demonstrated that ectopic expression of FAT-2 in TRPA1-expressing neurons led to decreases in preferred temperature by modulating neuronal activity. We conclude that functional expression of FAT-2 in a subset of neurons changes the thermoregulatory behaviour of D. melanogaster, likely by modulating quantities of PUFA-containing phospholipids in neuronal cell membranes. Polyunsaturated fatty acids (PUFAs) contain multiple double bonds in their hydrocarbon chains and, as bioactive lipids, regulate various animal physiological functions, such as those relating to immunity, reproduction and energy metabolism 1,2. PUFAs have also been implicated in thermal adaptation, particularly cold adaptation, because the cis double bonds in PUFAs create the "kinks" in hydrocarbon chain structures that reduce the packing of phospholipids, thus increasing membrane fluidity at low temperatures 3,4. For instance, ectothermic fish that live in low temperatures have high PUFA contents in phospholipids 5,6 , facilitating membrane fluidity 7 and modulating the activities of membrane proteins, such as Na +-K + ATPase 8 , in cold environments. Most organisms produce mono-unsaturated fatty acids from saturated fatty acids through the actions of Δ9 fatty acid desaturases 9-13. In mammals, PUFAs such as arachidonic acid [C20:4 (n-6)] and eicosapentaenoic acid [C20:5 (n-3)] are produced from linoleic acid [C18:2 (n-6)] and α-linolenic acid [C18:3 (n-3)], respectively, by Δ5 and Δ6 fatty acid desaturases. In contrast, Δ12 fatty acid desaturases that convert oleic acid [C18:1 (n-9)] to C18:2 (n-6), such as those in nematode Caenorhabditis elegans 14 , American cockroach 15 and cricket 16 , are found in few animals. Therefore, most animals have to obtain PUFAs, such as C18:2 (n-6) and C18:3 (n-3), from their diet. In bacteria 17 , protozoa 18 , algae 19,20 and plants 21,22 , Δ12 fatty acid desaturase can be reportedly induced following exposures to low temperatures. Hence, its biosynthetic product C18:2 (n-6) is thought to play crucial roles in low-temperature acclimation. C. elegans synthesises PUFAs using seven desaturases (FAT-1, FAT-2, FAT-3, FAT-4, FAT-5, FAT-6, ...

It is commonly observed that freshwater fish contain lower amounts of omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs), such as eicosapentaenoic acid (EPA, C20:5n-3) and docosahexaenoic acid (DHA, C22:6n-3), than marine fish species. In this study, we performed a detailed comparative analysis of phospholipids (PLs) and triacylglycerols (TAGs) from Gymnogobius isaza, a freshwater goby endemic to Lake Biwa inhabiting the lake bottom, and Gymnogobius urotaenia, a related goby that inhabits the shore of Lake Biwa. We found that tissues from G. isaza contain remarkably high amounts of omega-3 LC-PUFAs in both PLs and TAGs. Mass spectrometry analysis of TAGs demonstrated that the most abundant TAG molecular species were TAG (16:0/18:1/20:5), followed by TAG (14:0/18:1/20:5), in which EPA is incorporated into TAG at either the sn-1 or sn-3 positions. We isolated cDNAs encoding acyl-CoA: diacylglycerol acyltransferase designated as GiDGAT1 and GiDGAT2, from G. isaza. Expression studies using a neutral lipid-deficient Saccharomyces cerevisiae mutant strain demonstrated that both GiDGAT1 and GiDGAT2 possessed diacylglycerol acyltransferase activity, and preferential incorporation of LC-PUFA into TAG was observed in the presence of GiDGAT1. This study revealed the novel lipid profiles of G. isaza and identified the enzymes that were involved in the production of PUFA-containing TAGs.

Commensal bacteria affect many aspects of host physiology. In this study, we focused on the role of commensal bacteria in the thermoregulatory behavior of Drosophila melanogaster. We demonstrated that the elimination of commensal bacteria caused an increase in the preferred temperature of Drosophila third-instar larvae without affecting the activity of transient receptor potential ankyrin 1 (TRPA1)-expressing thermosensitive neurons. We isolated eight bacterial strains from the gut and culture medium of conventionally reared larvae and found that the preferred temperature of the larvae was decreased by mono-association with Lactobacillus plantarum or Corynebacterium nuruki. Mono-association with these bacteria did not affect the indices of energy metabolism such as ATP and glucose levels of larvae, which are closely linked to thermoregulation in animals. Thus, we show a novel role for commensal bacteria in host thermoregulation and identify two bacterial species that affect thermoregulatory behavior in Drosophila.