Bioproduction of n-3 polyunsaturated fatty acids by nematode fatty acid desaturases and elongase in Drosophila melanogaster.

n-3 polyunsaturated fatty acids (n-3 PUFAs), including α-linolenic acid and eicosapentaenoic acid (EPA), are essential nutrients for vertebrates including humans. Vertebrates are n-3 PUFA-auxotrophic; hence, dietary intake of n-3 PUFAs is required for their normal physiology and development. Although fish meal and oil have been utilized as primary sources of n-3 PUFAs by humans and aquaculture, these traditional n-3 PUFA sources are expected to be exhausted because of the increasing consumption requirements of humans. Hence, it is necessary to establish alternative n-3 PUFA sources to reduce the gap between the supply and demand of n-3 PUFAs. Here, we investigated whether insects, which are considered as a novel source of essential nutrients, could store n-3 PUFAs by the forced expression of n-3 PUFA biosynthetic enzymes. We utilized Drosophila as an insect model to generate transgenic strains expressing Caenorhabditis elegans PUFA biosynthetic enzymes and examined their effects on the proportion of fatty acids. The ubiquitous expression of methyl-end desaturase FAT-1 prominently enhanced the proportions of α-linolenic acid, indicating that FAT-1 is useful for metabolic engineering to fortify α-linolenic acid in insect. Furthermore, the ubiquitous expression of nematode front-end desaturases (FAT-3 and FAT-4), PUFA elongase (ELO-1), and FAT-1 led to EPA bioproduction. Hence, nematode PUFA biosynthetic genes may serve as powerful genetic tools for enhancing the proportion of EPA in insects. This study represents the first step toward the establishment of n-3 PUFA-producing insects.

Chaperonin TRiC/CCT supports mitotic exit and entry into endocycle in Drosophila.

Endocycle is a commonly observed cell cycle variant through which cells undergo repeated rounds of genome DNA replication without mitosis. Endocycling cells arise from mitotic cells through a switch of the cell cycle mode, called the mitotic-to-endocycle switch (MES), to initiate cell growth and terminal differentiation. However, the underlying regulatory mechanisms of MES remain unclear. Here we used the Drosophila steroidogenic organ, called the prothoracic gland (PG), to study regulatory mechanisms of MES, which is critical for the PG to upregulate biosynthesis of the steroid hormone ecdysone. We demonstrate that PG cells undergo MES through downregulation of mitotic cyclins, which is mediated by Fizzy-related (Fzr). Moreover, we performed a RNAi screen to further elucidate the regulatory mechanisms of MES, and identified the evolutionarily conserved chaperonin TCP-1 ring complex (TRiC) as a novel regulator of MES. Knockdown of TRiC subunits in the PG caused a prolonged mitotic period, probably due to impaired nuclear translocation of Fzr, which also caused loss of ecdysteroidogenic activity. These results indicate that TRiC supports proper MES and endocycle progression by regulating Fzr folding. We propose that TRiC-mediated protein quality control is a conserved mechanism supporting MES and endocycling, as well as subsequent terminal differentiation.

The presence of odd-chain fatty acids in Drosophila phospholipids.

Most fatty acids in phospholipids and other lipid species carry an even number of carbon atoms. Also odd-chain fatty acids (OCFAs), such as C15:0 and C17:0, are widespread throughout the living organism. However, the qualitative and quantitative profiles of OCFAs-containing lipids in living organisms remain unclear. Here, we show that OCFAs are present in Drosophila phosphatidylcholine (PC) and phosphatidylethanolamine (PE) and that their level increases in accordance with progression of growth. Furthermore, we found that food-derived propionic acid/propanoic acid (C3:0) is utilized for production of OCFA-containing PC and PE. This study provides the basis for understanding in vivo function of OCFA-containing phospholipids in development and lipid homeostasis.

Autocrine regulation of ecdysone synthesis by ß3-octopamine receptor in the prothoracic gland is essential for Drosophila metamorphosis.

In Drosophila, pulsed production of the steroid hormone ecdysone plays a pivotal role in developmental transitions such as metamorphosis. Ecdysone production is regulated in the prothoracic gland (PG) by prothoracicotropic hormone (PTTH) and insulin-like peptides (Ilps). Here, we show that monoaminergic autocrine regulation of ecdysone biosynthesis in the PG is essential for metamorphosis. PG-specific knockdown of a monoamine G protein-coupled receptor, ß3-octopamine receptor (Octß3R), resulted in arrested metamorphosis due to lack of ecdysone. Knockdown of tyramine biosynthesis genes expressed in the PG caused similar defects in ecdysone production and metamorphosis. Moreover, PTTH and Ilps signaling were impaired by Octß3R knockdown in the PG, and activation of these signaling pathways rescued the defect in metamorphosis. Thus, monoaminergic autocrine signaling in the PG regulates ecdysone biogenesis in a coordinated fashion on activation by PTTH and Ilps. We propose that monoaminergic autocrine signaling acts downstream of a body size checkpoint that allows metamorphosis to occur when nutrients are sufficiently abundant.

Polymorphism in microRNA-binding site in HNF1B influences the susceptibility of type 2 diabetes mellitus: a population based case-control study.

BACKGROUND: Recent genome-wide association studies (GWAS) have identified many SNPs associated with type 2 diabetes mellitus (T2DM). However, the functional roles for most of the SNPs have not been elucidated. MicroRNAs (miRNAs) are key regulators of gene expression involved in the development and progression of various diseases including T2DM. In this study, we investigated whether commonly occurring SNPs modulate miRNA-directed regulation of gene expression, and whether such SNPs in miRNA-binding sites are associated with the susceptibility for T2DM. METHODS: Genotypes of eleven 3' untranslated region (UTR) SNPs of seven susceptibility genes for T2DM were determined in 353 T2DM patients and 448 control subjects. In addition, the interactions of miRNAs with the 3'UTR in the hepatocyte nuclear factor 1ß (HNF1B) gene were investigated using luciferase reporter assays. RESULTS: One 3'UTR SNP (rs2229295) in the HNF1B gene was significantly associated with T2DM, and the frequency of an A allele (rs2229295) in T2DM patients was decreased compared with that in controls. Luciferase reporter assays showed that the SNP (rs2229295) altered the binding of two miRNAs (hsa-miR-214-5p and hsa-miR-550a-5p). CONCLUSIONS: We have detected the interactions of hsa-miR-214-5p/hsa-miR-550a-5p and the 3'UTR SNP of the HNF1B gene by in vitro luciferase reporter assays, and propose that the binding of such miRNAs regulates the expression of the HNF1B gene and the susceptibility of T2DM.

A heteroallelic Drosophila insulin-like receptor mutant and its use in validating physiological activities of food constituents.

Here we report an additional Drosophila transheterozygote InR(GS15311)/InR(GS50346) carrying two different P-element-inducible alleles of insulin-like receptor gene (InR). InR(GS15311)/InR(GS50346) flies exhibit the following phenotypes previously reported in InR and insulin/IGF-1 signaling (IIS) pathway-related gene mutants: small bodies, developmental delay, shortened lifespan, and increased fasting resistance. All of these characteristics are shared among flies carrying mutated genes implicated in the pathway. This heteroallelic combination exhibited fertility but resulted in male semilethality, while females were viable and grew into adults. Furthermore, an experimental model employing the InR(GS15311)/InR(GS50346) strain confirmed negligible involvement of royal jelly in IIS. Thus, the heteroallelic InR mutant, discovered in this study, will serve as a good model for multiple purposes: investigating the IIS mechanisms; identifying and validating the ingredients that prevent type II diabetes; and screening of food constituents associated with IIS.

Effect of a dipeptide-enriched diet in an adult Drosophila melanogaster laboratory strain.

Here we present free amino acid profiles for Drosophila melanogaster adults. Imidazol dipeptides anserine and carnosine, which are abundant in mammalian muscle tissue, are not present in Drosophila. Dipeptide-enriched food altered the amino acid balance, suggesting that the free amino acid content is nutrition-dependent and probably mediated by dipeptides.

The combined effects of genetic variation in the SIRT1 gene and dietary intake of n-3 and n-6 polyunsaturated fatty acids on serum LDL-C and HDL-C levels: a population based study.

BACKGROUND: Dyslipidemia due to high total cholesterol, LDL-cholesterol, triglycerides, or low HDL-cholesterol is an important risk factor for coronary heart disease (CHD). Both SIRT1 and PUFAs can influence the expression of genes for nuclear receptors and transcription factors related to lipid metabolism such as LXRα, LXRß, PPARα, SREBP-1c. METHODS: A total of 707 Japanese males and 723 females were randomly selected from the participants who visited a medical center for routine medical check-ups. We analyzed the combined effects of the genotype/haplotype of the SIRT1 gene and dietary n-6/n-3 PUFA intake ratio on the determination of serum lipid levels. RESULTS: We found that the SIRT1 gene marked with haplotype 2 was associated with decreased serum LDL-cholesterol and increased HDL-cholesterol levels. In addition, the associations between the SIRT1 haplotype 2 and decreased LDL-C and increased HDL-C levels were only observed in the low n-6/n-3 PUFA intake ratio group, but not in the high n-6/n-3 PUFA intake ratio group. CONCLUSIONS: Our findings indicate that the combination of genetic variation in the SIRT1 gene and dietary n-6 and/or n-3 PUFA intake influence the determination of inter-individual variations of serum levels of LDL-C and HDL-C.

The combined effect of the T2DM susceptibility genes is an important risk factor for T2DM in non-obese Japanese: a population based case-control study.

BACKGROUND: Type 2 diabetes mellitus (T2DM) is a complex endocrine and metabolic disorder. Recently, several genome-wide association studies (GWAS) have identified many novel susceptibility loci for T2DM, and indicated that there are common genetic causes contributing to the susceptibility to T2DM in multiple populations worldwide. In addition, clinical and epidemiological studies have indicated that obesity is a major risk factor for T2DM. However, the prevalence of obesity varies among the various ethnic groups. We aimed to determine the combined effects of these susceptibility loci and obesity/overweight for development of T2DM in the Japanese. METHODS: Single nucleotide polymorphisms (SNPs) in or near 17 susceptibility loci for T2DM, identified through GWAS in Caucasian and Asian populations, were genotyped in 333 cases with T2DM and 417 control subjects. RESULTS: We confirmed that the cumulative number of risk alleles based on 17 susceptibility loci for T2DM was an important risk factor in the development of T2DM in Japanese population (P<0.0001), although the effect of each risk allele was relatively small. In addition, the significant association between an increased number of risk alleles and an increased risk of T2DM was observed in the non-obese group (P<0.0001 for trend), but not in the obese/overweight group (P=0.88 for trend). CONCLUSIONS: Our findings indicate that there is an etiological heterogeneity of T2DM between obese/overweight and non-obese subjects.

Expression of ß-adrenergic-like octopamine receptors during Drosophila development.

An invertebrate biogenic amine, octopamine, plays diverse roles in multiple physiological processes (e.g. neurotransmitter, neuromodulator, and circulating neurohormone). Octopamine is thought to function by binding to G-protein-coupled receptors. In Drosophila, three ß-adrenergic-like octopamine receptors (Octß1R, Octß2R, and Octß3R) have been identified. We investigated the expression of three OctßR genes in embryos, larvae, and adults. These OctßRs showed distinct expression patterns in the central nervous system (CNS) throughout development, and Octß3R expression was evident in an endocrine organ, the ring gland, in larvae. In larvae, Octß1R, Octß2R, and Octß3R were expressed in salivary glands and imaginal discs, Octß2R and Octß3R in midgut, and Octß3R in gonads. In adult, besides in the CNS, each OctßR was strongly expressed in ovary and testis. Our findings provide a basis for understanding the mechanisms by which OctßRs mediate multiple diverse octopaminergic functions during development.

Freeze-dried royal jelly maintains its developmental and physiological bioactivity in Drosophila melanogaster.

Royal jelly (RJ), a honeybee-derived product, has been found to possess developmental and physiological bioactivity in the fruit fly, Drosophila melanogaster, but little is known about the in vivo bioactivity of freeze-dried RJ (FDRJ) powder, which is another form of RJ processed for human use. To address this, we used Drosophila as a model animal to examine the effects of FDRJ in multicellular organisms. When flies were reared on food supplemented with FDRJ, the developmental time from larva to adult was shortened, the adult male lifespan was prolonged, and female fecundity was increased without any significant morphological alterations. Moreover, the expression of dilp5, an insulin-like peptide, its receptor InR, and the nutrient sensing molecule TOR, the target of rapamycin, was significantly increased in FDRJ-fed female flies as compared with ones reared on standard and on protein-enriched food. These findings suggest that like RJ, FDRJ maintains its bioactivity even after processing from RJ, what is expected to have bioactivity for multicellular organisms, including humans.

Su(var)2-10- and Su(var)205-dependent upregulation of the heterochromatic gene neverland is required for developmental transition in Drosophila.

Animals develop from juveniles to sexually mature adults through the action of steroid hormones. In insect metamorphosis, a surge of the steroid hormone ecdysone prompts the transition from the larval to the adult stage. Ecdysone is synthesized by a series of biosynthetic enzymes that are specifically expressed in an endocrine organ, the prothoracic gland. At the late larval stage, the expression levels of ecdysone biosynthetic enzymes are upregulated through the action of numerous transcription factors, thus initiating metamorphosis. In contrast, the mechanism by which chromatin regulators support the expression of ecdysone biosynthetic genes is largely unknown. Here, we demonstrate that Su(var)2-10 and Su(var)205, suppressor of variegation [Su(var)] genes encoding a chromatin regulator Su(var)2-10 and nonhistone heterochromatic protein 1a, respectively, regulate the transcription of one of the heterochromatic ecdysone biosynthetic genes, neverland, in Drosophila melanogaster. Knockdown of Su(var)2-10 and Su(var)205 in the prothoracic gland caused a decrease in neverland expression, resulting in a defect in larval-to-prepupal transition. Furthermore, overexpression of neverland and administration of 7-dehydrocholesterol, a biosynthetic precursor of ecdysone produced by Neverland, rescued developmental defects in Su(var)2-10 and Su(var)205 knockdown animals. These results indicate that Su(var)2-10- and Su(var)205-mediated proper expression of neverland is required for the initiation of metamorphosis. Given that Su(var)2-10-positive puncta are juxtaposed with the pericentromeric heterochromatic region, we propose that Su(var)2-10- and Su(var)205-dependent regulation of inherent heterochromatin structure at the neverland gene locus is essential for its transcriptional activation.

Influences of the Interactions of Genetic Variations of Seven Core Circadian Clock Genes with Lifestyle Factors on Metabolic Parameters.

INTRODUCTION: In mammals, circadian rhythms regulate many behavioral and physiological processes. Genetic and epidemiological studies have shown that dysregulation of the circadian rhythm induces chronic metabolic diseases, such as obesity, diabetes, and dyslipidemia. We aimed to know the interactions of genetic variations of seven core circadian clock genes with lifestyle factors on the determination of metabolic parameters. METHODS: We have analyzed the impacts of genotype of seven core circadian clock genes (i.e., CLOCK, BMAL1, PER1, PER2, PER3, CRY1, and CRY2) and lifestyle factors (i.e., physical activity and sleep duration) in 575 Japanese males on the determination of metabolic parameters (i.e., body mass index [BMI], serum glucose, glycated hemoglobin [HbA1c], low-density lipoprotein cholesterol [LDL-C], and high-density lipoprotein cholesterol [HDL-C] levels). RESULTS: We have detected the associations between genotypes of PER3 and serum HbA1c level and genotypes of CRY1 and serum LDL-C level. Additionally, the interactions of the genotypes of PER1 and PER3 with physical activity for determining BMI, the genotypes of CLOCK with physical activity for determining serum HbA1c levels were observed. Furthermore, for determining serum HDL-C levels, the interactions of the genotypes of CRY2 with physical activity or sleep duration were observed. DISCUSSION/CONCLUSION: Our findings indicate that the interactions of genotypes for core circadian clock genes and lifestyle factors (i.e., physical activity and sleep duration) are important for determining metabolic parameters.

The Nutrient-Responsive Molecular Chaperone Hsp90 Supports Growth and Development in Drosophila.

Animals can sense internal nutrients, such as amino acids/proteins, and are able to modify their developmental programs in accordance with their nutrient status. In the fruit fly, Drosophila melanogaster, amino acid/protein is sensed by the fat body, an insect adipose tissue, through a nutrient sensor, target of rapamycin (TOR) complex 1 (TORC1). TORC1 promotes the secretion of various peptide hormones from the fat body in an amino acid/protein-dependent manner. Fat-body-derived peptide hormones stimulate the release of insulin-like peptides, which are essential growth-promoting anabolic hormones, from neuroendocrine cells called insulin-producing cells (IPCs). Although the importance of TORC1 and the fat body-IPC axis has been elucidated, the mechanism by which TORC1 regulates the expression of insulinotropic signal peptides remains unclear. Here, we show that an evolutionarily conserved molecular chaperone, heat shock protein 90 (Hsp90), promotes the expression of insulinotropic signal peptides. Fat-body-selective Hsp90 knockdown caused the transcriptional downregulation of insulinotropic signal peptides. IPC activity and systemic growth were also impaired in fat-body-selective Hsp90 knockdown animals. Furthermore, Hsp90 expression depended on protein/amino acid availability and TORC1 signaling. These results strongly suggest that Hsp90 serves as a nutrient-responsive gene that upregulates the fat body-IPC axis and systemic growth. We propose that Hsp90 is induced in a nutrient-dependent manner to support anabolic metabolism during the juvenile growth period.

Loss of CNDP causes a shorter lifespan and higher sensitivity to oxidative stress in Drosophila melanogaster.

Increasing oxidative stress seems to be the result of an imbalance between free radical production and antioxidant defenses. During the course of aging, oxidative stress causes tissue/cellular damage, which is implicated in numerous age-related diseases. Carnosinase (CN or CNDP) is dipeptidase, which is associated with carnosine and/or glutathione (GSH) metabolism, those are the most abundant naturally occurring endogenous dipeptide and tripeptides with antioxidant and free radical scavenger properties. In the present study, we generated Drosophila cndp (dcndp) mutant flies using the CRISPR/Cas9 system to study the roles of dcndp in vivo. We demonstrate that dcndp mutant flies exhibit shorter lifespan and increased sensitivity to paraquat or hydrogen peroxide (H2O2) induced oxidative stress. These results suggest that dcndp maintains homeostatic conditions, protecting cells and tissues against the harmful effects of oxidative stress in the course of aging.

Omega-3 Eicosapentaenoic Acid Is Related to Happiness and a Sense of Fulfillment-A Study among Female Nursing Workers.

Background: Omega (ω) 3 fatty acid (FA) is a polyunsaturated FA (PUFA) that can modulate some mental statuses. However, most studies have not considered the functional differences between eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). We investigated associations among happiness, a sense of fulfillment and serum ω3 PUFA levels. Methods: Participants were 133 female staff from a hospital and nursing homes. Happiness was measured using the Japanese version of the subjective happiness scale (SHS); a sense of fulfillment was assessed using a visual analogue scale. Serum FA concentrations were measured. A partial correlation test and a regression model were applied. Results: The SHS scores showed significantly positive correlations with a sense of fulfillment, DHA% and EPA% (p < 0.05, < 0.05 and < 0.005, respectively), after controlling for age, BMI, menopause, snacking habits and leisure-time physical activities. A sense of fulfillment was significantly negatively correlated with α-linoleic acid%, and positively correlated with DHA% and EPA% (p < 0.05, < 0.05 and < 0.005, respectively), after controlling for the confounders. A regression model showed that a sense of fulfillment, EPA, and not stopping menstruation explained happiness (standardised beta, B = 0.18, p < 0.05; B = 0.24, p < 0.01; and B = 0.32, and p < 0.05, respectively), whereas age, BMI and snacking habits could not. Simultaneously, a regression model could not explain the association between DHA and happiness. Conclusion: Happiness was related with serum EPA%, a sense of fulfillment, and premenopause.

Variations in the WNK1 gene modulates the effect of dietary intake of sodium and potassium on blood pressure determination.

WNK lysine-deficient protein kinase 1 (WNK1) is a member of the WNK family of serine/threonine kinases with no lysine (K), and these kinases have been implicated as important modulators of salt homeostasis in the kidney. It is well known that high dietary sodium and low dietary potassium have been implicated in the etiology of increased blood pressure. However, the blood pressure response to dietary sodium and potassium intake varies considerably among individuals. In this study, we have detected that the haplotypes of the WNK1 gene are associated with blood pressure variations in the general Japanese population. In addition, we investigated the interactions between the haplotypes of the WNK1 gene and dietary sodium and potassium intake for determining inter-individual variations in blood pressure. Our data support the hypothesis that part of the variation in blood pressure response to dietary sodium and potassium intake among individuals can be explained by variations in the WNK1 gene.

Serum IL-6 levels and oxidation rate of LDL cholesterol were related to depressive symptoms independent of omega-3 fatty acids among female hospital and nursing home workers in Japan.

BACKGROUND: Chronic low-grade inflammation and oxidative stress are commonly observed in persons with depression or depressive symptoms. We explored the degree of depressive symptoms under psychological stress in relation to serum LDL oxidation, inflammatory markers, and fatty acid (FA) distribution among female population. The purpose of this study was to identify peripheral factors that are related to depressive symptoms, and to assess how each factor is related to depressive symptoms. METHODS: 133 female workers in a hospital and nursing homes were recruited in Japan. Depressive symptoms were assessed using the Japanese version of the Centre for Epidemiologic Studies Depression Scale (CES-D), and perceived stress was assessed using the visual analogue scale. Cytokine levels and oxidation rate of LDL cholesterol (ox-LDL/LDL) were measured as indices of inflammation and oxidation. Omega-3 FA distribution was also measured. Path analysis and hierarchical regression analysis were used to determine if each factor was predictive of depressive symptoms. RESULTS: It was identified that serum ox-LDL/LDL was positively connected with depressive symptoms, but was more strongly related to perceived psychological stress. Elevated serum IL-6 was positively correlated with depressive symptoms, though the effect was partly transmitted via ox-LDL/LDL. Additionally, serum ω3 PUFAs were inversely associated with depressive symptoms independently of IL-6 or ox-LDL/LDL. CONCLUSION: Although this study is unlikely to fully explain the causes of depressive symptoms, it suggests that psychological stress and somatic factors such as inflammation, oxidation and nutrition are related to depressive symptoms. These findings suggest the therapeutic potential of lifestyle targets to alleviate the identified depression risk factors, anti-oxidative therapies, anti-inflammatory therapies and nutritional interventions to prevent depression.

Adult-specific insulin-producing neurons in Drosophila melanogaster.

Holometabolous insects undergo metamorphosis to reorganize their behavioral and morphological features into adult-specific ones. In the central nervous system (CNS), some larval neurons undergo programmed cell death, whereas others go through remodeling of axonal and dendritic arbors to support functions of re-established adult organs. Although there are multiple neuropeptides that have stage-specific roles in holometabolous insects, the reorganization pattern of the entire neuropeptidergic system through metamorphosis still remains largely unclear. In this study, we conducted a mapping and lineage tracing of peptidergic neurons in the larval and adult CNS by using Drosophila genetic tools. We found that Diuretic hormone 44-producing median neurosecretory cells start expressing Insulin-like peptide 2 in the pharate adult stage. This neuronal cluster projects to the corpora cardiaca and dorsal vessel in both larval and adult stages, and also innervates an adult-specific structure in the digestive tract, the crop. We propose that the adult-specific insulin-producing cells may regulate functions of the digestive system in a stage-specific manner. Our study provides a neuroanatomical basis for understanding remodeling of the neuropeptidergic system during insect development and evolution.

Perceived 6-n-Propylthiouracil (PROP) Bitterness Is Associated with Dietary Sodium Intake in Female Japanese College Students.

Despite the negative health consequences of a high sodium consumption, humans consume well above the recommended levels. This study examines whether or not the dietary intake of sodium was affected by individual variation of the perceived bitterness of 6-n-propylthiouracil (PROP), and examines the relationship between the perceived bitterness of PROP and the preferred NaCl concentration of broth. Female students (20-22 y old) were recruited from the university community. Genotypes of A49P and I296V polymorphism of the TAS2R38 bitter taste receptor were determined for each subject. Samples containing NaCl, PROP or broth in 5-mL portions were evaluated by sensory testing. The participants completed a food record for each diet. Our results indicate that the individuals perceiving PROP to be more bitter had consumed a greater amount of dietary sodium. In contrast, there was no significant positive correlation between an individual's perceived saltiness and the dietary sodium intake. Those who perceived PROP to be more bitter preferred a broth containing a higher concentration of NaCl. All of these correlations were apparent even after those subjects with TAS2R38 AI/AI homozygotes (PROP non-taster) had been excluded. In conclusion, the results of this study suggest that a factor affecting the bitter rating of PROP other than the AI/AI homozygotes of TAS2R38 contributes to the variation in sodium intake and the preference for salty food.