Sensing of the non-essential amino acid tyrosine governs the response to protein restriction in Drosophila

From sensory organs to internal pathways: A comprehensive review of amino acid sensing in Drosophila

Organisms require various nutrients to provide energy, support growth, and maintain metabolic balance. Amino acid is among the most basic nutrients, serving as fundamental building blocks for protein synthesis while playing vital roles in growth, development, and reproduction. Understanding the mechanisms by which organisms perceive amino acids is key to unraveling how they select appropriate food sources and adapt to environmental challenges. The fruit fly, Drosophila melanogaster, serves as a powerful model for understanding fundamental genetic and physiological processes. This review focuses on recent advances in amino acid sensing mechanisms in Drosophila melanogaster and their relevance to feeding behavior, nutrient homeostasis, and adaptive responses, and integrates insights into peripheral sensory systems, such as the legs and proboscis, as well as internal regulatory mechanisms within the gut, fat body, and brain. It highlights key molecular players, including ionotropic receptors, gut-derived hormones, neuropeptides, and the microbiome-gut-brain axis. Additionally, the manuscript identifies knowledge gaps and proposes directions for future research, providing a comprehensive overview of this dynamic field.

Selection for Early Reproduction Leads to Accelerated Aging and Extensive Metabolic Remodeling in Drosophila melanogaster

Experimental evolution studies that feature selection on life-history characters are a proven approach for studying the evolution of aging and variation in rates of senescence. Recently, the incorporation of genomic and transcriptomic approaches into this framework has led to the identification of hundreds of genes associated with different aging patterns. However, our understanding of the specific molecular mechanisms underlying these aging patterns remains limited. Here, we incorporated extensive metabolomic profiling into this framework to generate mechanistic insights into aging patterns in Drosophila melanogaster. Specifically, we characterized metabolomic change over adult lifespan in populations of D. melanogaster where selection for early reproduction has led to an accelerated aging phenotype relative to their controls. Using these data, we (i) evaluated evolutionary repeatability across the metabolome; (ii) assessed the value of the metabolome as a predictor of "biological age" in this system; and (iii) identified specific metabolites associated with accelerated aging. Generally, our findings suggest that selection for early reproduction resulted in highly repeatable alterations to the metabolome and the metabolome itself is a reliable predictor of "biological age". Specifically, we find clusters of metabolites that are associated with the different rates of senescence observed between our accelerated aging population and their controls, adding new insights into the metabolites that may be driving the accelerated aging phenotype.

Protein-responsive gut hormone tachykinin directs food choice and impacts lifespan

Animals select food based on hungers that reflect dynamic macronutrient needs, but the hormonal mechanisms underlying nutrient-specific appetite regulation remain poorly defined. Here, we identify tachykinin (Tk) as a protein-responsive gut hormone in Drosophila and female mice, regulated by conserved environmental and nutrient-sensing mechanisms. Protein intake activates Tk-expressing enteroendocrine cells (EECs), driving the release of gut Tk through mechanisms involving target of rapamycin (TOR) and transient receptor potential A1 (TrpA1). In flies, we delineate a pathway by which gut Tk controls selective appetite and sleep after protein ingestion, mediated by glucagon-like adipokinetic hormone (AKH) signalling to neurons and adipose tissue. This mechanism suppresses protein appetite, promotes sugar hunger and modulates wakefulness to align behaviour with nutritional needs. Inhibiting protein-responsive gut Tk prolongs lifespan through AKH, revealing a role for nutrient-dependent gut hormone signalling in longevity. Our results provide a framework for understanding EEC-derived nutrient-specific satiety signals and the role of gut hormones in regulating food choice, sleep and lifespan.

Comparative Transcriptome Analysis Reveals the Effects of a High-Protein Diet on Silkworm Midgut

The silkworm is a species within the order Lepidoptera and an economic insect. The nutrients are obtained from the leaf and utilized by the silkworm larvae for body growth, development, and cocoon formation. Protein plays a significant functional role in the diet of silkworms. To investigate the impact of the high-protein diet (HPD 6%) on silkworm growth and development, transcriptomic analysis was conducted on the silkworm midgut, and 1724 differentially expressed genes (DEGs) were identified, comprising 803 up-regulated genes and 921 down-regulated genes. The up-regulated genes exhibited the majority pathway of mitochondrial oxidative phosphorylation, ribosome, and ribosome biogenesis in eukaryotes. The down-regulated genes of DEGs were mostly annotated in ABC transporters, lysosome, endocytosis, and sphingolipid metabolism pathways. The comprehensive analysis of DEGs indicated that substantial modifications were observed in various pathways associated with crucial biological processes. HPD 6% decreased oxidative stress and increased mitochondrial activity, ribosomal activity, and DNA repair capacity. Additionally, the ATP levels were increased in the midgut, malpighian tubule, middle silk gland, and posterior silk gland of the HPD 6% group. Moreover, the activities of SOD and NADH were enhanced in the midgut of the HPD 6% group. Our findings provide valuable insights into the wide-ranging effects of an HPD treatment in insects such as silkworms.

Gap junctions allow transfer of metabolites between germ cells and somatic cells to promote germ cell growth in the Drosophila ovary

Gap junctions allow the exchange of small molecules between cells. How this function could be used to promote cell growth is not yet fully understood. During Drosophila ovarian follicle development, germ cells, which are surrounded by epithelial somatic cells, undergo massive growth. We found that this growth depends on gap junctions between these cell populations, with a requirement for Innexin4 and Innexin2, in the germ cells and the somatic cells, respectively. Translatomic analyses revealed that somatic cells express enzymes and transporters involved in amino acid metabolism that are absent in germ cells. Among them, we identified a putative amino acid transporter required for germline growth. Its ectopic expression in the germline can partially compensate for its absence or the one of Innexin2 in somatic cells. Moreover, affecting either gap junctions or the import of some amino acids in somatic cells induces P-bodies in the germ cells, a feature usually associated with an arrest of translation. Finally, in somatic cells, innexin2 expression and gap junction assembly are regulated by the insulin receptor/PI3K kinase pathway, linking the growth of the two tissues. Overall, these results support the view that metabolic transfer through gap junction promotes cell growth and illustrate how such a mechanism can be integrated into a developmental program, coupling growth control by extrinsic systemic signals with the intrinsic coordination between cell populations.

Dysfunctional BCAA degradation triggers neuronal damage through disrupted AMPK-mitochondrial axis due to enhanced PP2Ac interaction

Metabolic and neurological disorders commonly display dysfunctional branched-chain amino acid (BCAA) metabolism, though it is poorly understood how this leads to neurological damage. We investigated this by generating Drosophila mutants lacking BCAA-catabolic activity, resulting in elevated BCAA levels and neurological dysfunction, mimicking disease-relevant symptoms. Our findings reveal a reduction in neuronal AMP-activated protein kinase (AMPK) activity, which disrupts autophagy in mutant brain tissues, linking BCAA imbalance to brain dysfunction. Mechanistically, we show that excess BCAA-induced mitochondrial reactive oxygen species (ROS) triggered the binding of protein phosphatase 2 A catalytic subunit (PP2Ac) to AMPK, suppressing AMPK activity. This initiated a dysregulated feedback loop of AMPK-mitochondrial interactions, exacerbating mitochondrial dysfunction and oxidative neuronal damage. Our study identifies BCAA imbalance as a critical driver of neuronal damage through AMPK suppression and autophagy dysfunction, offering insights into metabolic-neuronal interactions in neurological diseases and potential therapeutic targets for BCAA-related neurological conditions.

A high-protein diet-responsive gut hormone regulates behavioral and metabolic optimization in Drosophila melanogaster

Protein is essential for all living organisms; however, excessive protein intake can have adverse effects, such as hyperammonemia. Although mechanisms responding to protein deficiency are well-studied, there is a significant gap in our understanding of how organisms adaptively suppress excessive protein intake. In the present study, utilizing the fruit fly, Drosophila melanogaster, we discover that the peptide hormone CCHamide1 (CCHa1), secreted by enteroendocrine cells in response to a high-protein diet (HPD), is vital for suppressing overconsumption of protein. Gut-derived CCHa1 is received by a small subset of enteric neurons that produce short neuropeptide F, thereby modulating protein-specific satiety. Importantly, impairment of the CCHa1-mediated gut-enteric neuronal axis results in ammonia accumulation and a shortened lifespan under HPD conditions. Collectively, our findings unravel the crosstalk of gut hormone and neuronal pathways that orchestrate physiological responses to prevent and adapt to dietary protein overload.

Sexually dimorphic ATF4 expression in the fat confers female stress tolerance in Drosophila melanogaster

Metabolic differences between males and females have been well documented across many species. However, the molecular basis of these differences and how they impact tolerance to nutrient deprivation is still under investigation. In this work, we use Drosophila melanogaster to demonstrate that sex-specific differences in fat tissue metabolism are driven, in part, by dimorphic expression of the Integrated Stress Response (ISR) transcription factor, ATF4. We found that female fat tissues have higher ATF4 activity than their male counter parts under homeostatic conditions. This dimorphism was partly due to a female bias in transcript abundance of specific ATF4 splice isoforms. We found that the canonical sex determinants transformer (tra) and doublesex (dsx) drive such dimorphic ATF4 transcript abundance. These differences persist in a genetic model of nutrient deprivation, where female animals showed greater resistance to lethality than males in an ATF4-dependent manner. These results suggest that higher ATF4 activity confers higher tolerance to stress in females. Together, our data describe a previously unknown facet of ISR signaling wherein sexual identity of adipose tissue confers differential stress tolerance in males and females. Since energy storage mechanisms are known to be dimorphic and have been linked to ATF4 regulation, our studies provide a mechanistic starting point for understanding how sexual identity influences metabolic disease outcomes.

Phenylalanine Regulates Milk Protein Synthesis via LAT1-mTOR Signaling Pathways in Bovine Mammary Epithelial Cells

Phenylalanine (Phe) is a potentially limiting amino acid for lactating cows. The mechanism by which Phe regulates milk protein synthesis remains unclear. The present study elucidates the mechanisms by which phenylalanine affects milk protein synthesis, amino acid utilization, and related signaling pathways in bovine mammary epithelial cells (BMECs). The BMECs were treated with five concentrations (0, 0.22, 0.44, 0.88, 1.76 mM, and serum free). Rapamycin inhibitors and RNA interference (RNAi) were used to inhibit the phosphorylation of the mammalian target of rapamycin (mTOR) signaling pathway and the expression of relevant amino acid transporters, respectively. The results showed that 4×Phe (0.88 mM) significantly increased (p < 0.05) both the mRNA and protein expression of α-casein (CSN1S1), β-casein (CSN2), and κ-casein (CSN3), as well as L-type amino acid transporter-1 (LAT1) mRNA expression. Protein expression and modification assays of mTOR-related proteins showed that 4×Phe could increase (p < 0.05) the expression of α-casein and eukaryotic initiation factor 4E-binding protein-1 (4EBP1) and tended to increase the expression of ribosomal protein S6 protein kinase (S6K1, p = 0.054). The general control nonderepressible 2 (GCN2) signaling pathway factor, eukaryotic initiation factor 2 (eIF2α), was downregulated by 4×Phe treatment (p < 0.05). The rapamycin inhibition test showed that Phe regulated casein synthesis via the mTOR signaling pathway. RNAi experiments showed that LAT1 mediated the entry of Phe into cells. Moreover, 4×Phe treatment tended to decrease (0.05 < p < 0.10) the consumption of valine, leucine, histidine, tyrosine, cysteine, alanine, asparagine, and serine in the medium. Collectively, phenylalanine enhanced α-casein synthesis by regulating the phosphorylation of 4EBP1 and eIF2α and promoting the formation of the mTOR-centered casein translation initiation complex.

Regulatory Mechanisms of Aging Through the Nutritional and Metabolic Control of Amino Acid Signaling in Model Organisms

Life activities are supported by the intricate metabolic network that is fueled by nutrients. Nutritional and genetic studies in model organisms have determined that dietary restriction and certain mutations in the insulin signaling pathway lead to lifespan extension. Subsequently, the detailed mechanisms of aging as well as various nutrient signaling pathways and their relationships have been investigated in a wide range of organisms, from yeast to mammals. This review summarizes the roles of nutritional and metabolic signaling in aging and lifespan with a focus on amino acids, the building blocks of organisms. We discuss how lifespan is affected by the sensing, transduction, and metabolism of specific amino acids and consider the influences of life stage, sex, and genetic background on the nutritional control of aging. Our goal is to enhance our understanding of how nutrients affect aging and thus contribute to the biology of aging and lifespan.

Context-dependent impact of the dietary non-essential amino acid tyrosine on Drosophila physiology and longevity

Dietary protein intake modulates growth, reproduction, and longevity by stimulating amino acid (AA)-sensing pathways. Essential AAs are often considered as limiting nutrients during protein scarcity, and the role of dietary non-essential AAs (NEAAs) is less explored. Although tyrosine has been reported to be crucial for sensing protein restriction in Drosophila larvae, its effect on adult physiology and longevity remains unclear. Here, using a synthetic diet, we perform a systematic investigation of the effect of single NEAA deprivation on nutrient-sensing pathways, reproductive ability, starvation resistance, feeding behavior, and life span in adult female flies. Specifically, dietary tyrosine deprivation decreases internal tyrosine levels and fecundity, influences AA-sensing machineries, and extends life span. These nutritional responses are not observed under higher total AA intake or in infertile female flies, suggesting a context-dependent influence of dietary tyrosine. Our findings highlight the unique role of tyrosine as a potentially limiting nutrient, underscoring its value for dietary interventions aimed at enhancing health span.

Misregulation of bromotyrosine compromises fertility in male Drosophila

Biological regulation often depends on reversible reactions such as phosphorylation, acylation, methylation, and glycosylation, but rarely halogenation. A notable exception is the iodination and deiodination of thyroid hormones. Here, we report detection of bromotyrosine and its subsequent debromination during Drosophila spermatogenesis. Bromotyrosine is not evident when Drosophila express a native flavin-dependent dehalogenase that is homologous to the enzyme responsible for iodide salvage from iodotyrosine in mammals. Deletion or suppression of the dehalogenase-encoding condet (cdt) gene in Drosophila allows bromotyrosine to accumulate with no detectable chloro- or iodotyrosine. The presence of bromotyrosine in the cdt mutant males disrupts sperm individualization and results in decreased fertility. Transgenic expression of the cdt gene in late-staged germ cells rescues this defect and enhances tolerance of male flies to bromotyrosine. These results are consistent with reversible halogenation affecting Drosophila spermatogenesis in a process that had previously eluded metabolomic, proteomic, and genomic analyses.

Dietary L-Glu sensing by enteroendocrine cells adjusts food intake via modulating gut PYY/NPF secretion

Amino acid availability is monitored by animals to adapt to their nutritional environment. Beyond gustatory receptors and systemic amino acid sensors, enteroendocrine cells (EECs) are believed to directly percept dietary amino acids and secrete regulatory peptides. However, the cellular machinery underlying amino acid-sensing by EECs and how EEC-derived hormones modulate feeding behavior remain elusive. Here, by developing tools to specifically manipulate EECs, we find that Drosophila neuropeptide F (NPF) from mated female EECs inhibits feeding, similar to human PYY. Mechanistically, dietary L-Glutamate acts through the metabotropic glutamate receptor mGluR to decelerate calcium oscillations in EECs, thereby causing reduced NPF secretion via dense-core vesicles. Furthermore, two dopaminergic enteric neurons expressing NPFR perceive EEC-derived NPF and relay an anorexigenic signal to the brain. Thus, our findings provide mechanistic insights into how EECs assess food quality and identify a conserved mode of action that explains how gut NPF/PYY modulates food intake.

The integrated stress response in metabolic adaptation

The integrated stress response (ISR) refers to signaling pathways initiated by stress-activated eIF2α kinases. Distinct eIF2α kinases respond to different stress signals, including amino acid deprivation and mitochondrial stress. Such stress-induced eIF2α phosphorylation attenuates general mRNA translation and, at the same time, stimulates the preferential translation of specific downstream factors to orchestrate an adaptive gene expression program. In recent years, there have been significant new advances in our understanding of ISR during metabolic stress adaptation. Here, I discuss those advances, reviewing among others the ISR activation mechanisms in response to amino acid deprivation and mitochondrial stress. In addition, I review how ISR regulates the amino acid metabolic pathways and how changes in the ISR impact the physiology and pathology of various disease models.

Hybrid quantum-classical polarizability model for single molecule biosensing

Optical whispering gallery mode biosensors are able to detect single molecules through effects of their polarizability. We address the factors that affect the polarizability of amino acids, which are the building blocks of life, via electronic structure theory. Amino acids are detected in aqueous environments, where their polarizability is different compared to the gasphase due to solvent effects. Solvent effects include structural changes, protonation and the local field enhancement through the solvent (water). We analyse the impact of these effects and find that all contribute to an increased effective polarizability in the solvent. We also address the excess polarizability relative to the displaced water cavity and develop a hybrid quantum-classical model that is in good agreement with self-consistent calculations. We apply our model to calculate the excess polarizability of 20 proteinogenic amino acids and determine the minimum resolution required to distinguish the different molecules and their ionised conformers based on their polarizability.

Mating-induced increase of kynurenine in Drosophila ovary enhances starvation resistance of progeny

The maternal nutritional environment can impact progeny development, stress tolerance, and longevity. Such phenotypic variation of offspring resulting from the maternal environment is often referred to as the 'maternal effect' and is observed across taxa, including in humans. While some mechanisms behind maternal effects have been revealed, such as histone modification, many studies rely on drastic genetic or nutritional manipulation in describing these mechanisms. Here we aimed to reveal how the maternal environment is regulated under physiological conditions to affect the progeny. Specifically, we detailed metabolic regulation in oocytes in response to mating using Drosophila melanogaster fruit flies. Using liquid chromatography-mass spectrometry, we found that upon mating, the ovary metabolites shifted, predominantly toward increasing amino acids and the tryptophan/kynurenine (Kyn) pathway. This mating-induced increase in ovary Kyn was driven by increased Kyn production in the fat body, a functional counterpart of the mammalian liver and white adipose tissue and the source of Kyn storage for the ovary after mating. Furthermore, we show that maternal Kyn repression decreased the starvation resistance of progeny and that administering exogenous Kyn to the maternal generation enhanced the starvation resistance of female progeny. Taken together, these findings point to a previously unidentified role of fat body Kyn distribution during reproduction on progeny survival.

Epidermal tyrosine catabolism is crucial for metabolic homeostasis and survival against high-protein diets in Drosophila

The insect epidermis forms the exoskeleton and determines the body size of an organism. How the epidermis acts as a metabolic regulator to adapt to changes in dietary protein availability remains elusive. Here, we show that the Drosophila epidermis regulates tyrosine (Tyr) catabolism in response to dietary protein levels, thereby promoting metabolic homeostasis. The gene expression profile of the Drosophila larval body wall reveals that enzymes involved in the Tyr degradation pathway, including 4-hydroxyphenylpyruvate dioxygenase (Hpd), are upregulated by increased protein intake. Hpd is specifically expressed in the epidermis and is dynamically regulated by the internal Tyr levels. Whereas basal Hpd expression is maintained by insulin/IGF-1 signalling, Hpd induction on high-protein diet requires activation of the AMP-activated protein kinase (AMPK)-forkhead box O subfamily (FoxO) axis. Impairment of the FoxO-mediated Hpd induction in the epidermis leads to aberrant increases in internal Tyr and its metabolites, disrupting larval development on high-protein diets. Taken together, our findings uncover a crucial role of the epidermis as a metabolic regulator in coping with an unfavourable dietary environment.

A distinct Acyl-CoA binding protein (ACBP6) shapes tissue plasticity during nutrient adaptation in Drosophila

Nutrient availability is a major selective force in the evolution of metazoa, and thus plasticity in tissue function and morphology is shaped by adaptive responses to nutrient changes. Utilizing Drosophila, we reveal that distinct calibration of acyl-CoA metabolism, mediated by Acbp6 (Acyl-CoA binding-protein 6), is critical for nutrient-dependent tissue plasticity. Drosophila Acbp6, which arose by evolutionary duplication and binds acyl-CoA to tune acetyl-CoA metabolism, is required for intestinal resizing after nutrient deprivation through activating intestinal stem cell proliferation from quiescence. Disruption of acyl-CoA metabolism by Acbp6 attenuation drives aberrant 'switching' of metabolic networks in intestinal enterocytes during nutrient adaptation, impairing acetyl-CoA metabolism and acetylation amid intestinal resizing. We also identified STAT92e, whose function is influenced by acetyl-CoA levels, as a key regulator of acyl-CoA and nutrient-dependent changes in stem cell activation. These findings define a regulatory mechanism, shaped by acyl-CoA metabolism, that adjusts proliferative homeostasis to coordinately regulate tissue plasticity during nutrient adaptation.

GCN2 mediates access to stored amino acids for somatic maintenance during Drosophila ageing

Many mechanistic theories of ageing argue that a progressive failure of somatic maintenance, the use of energy and resources to prevent and repair damage to the cell, underpins ageing. To sustain somatic maintenance an organism must acquire dozens of essential nutrients from the diet, including essential amino acids (EAAs), which are physiologically limiting for many animals. In Drosophila , adulthood deprivation of each individual EAA yields vastly different lifespan trajectories, and adulthood deprivation of one EAA, phenylalanine (Phe), has no associated lifespan cost; this is despite each EAA being strictly required for growth and reproduction. Moreover, survival under any EAA deprivation depends entirely on the conserved AA sensor GCN2, a component of the integrated stress response (ISR), suggesting that a novel ISR-mediated mechanism sustains lifelong somatic maintenance during EAA deprivation. Here we investigated this mechanism, finding that flies chronically deprived of dietary Phe continue to incorporate Phe into new proteins, and that challenging flies to increase the somatic requirement for Phe shortens lifespan under Phe deprivation. Further, we show that autophagy is required for full lifespan under Phe deprivation, and that activation of the ISR can partially rescue the shortened lifespan of GCN2 -nulls under Phe deprivation. We therefore propose a mechanism by which GCN2, via the ISR, activates autophagy during EAA deprivation, breaking down a larvally-acquired store of EAAs to support somatic maintenance. These data refine our understanding of the strategies by which flies sustain lifelong somatic maintenance, which determines length of life in response to changes in the nutritional environment.

eIF3 subunit M regulates blood meal digestion in Rhodnius prolixus affecting ecdysis, reproduction, and survival

In triatomines, blood-feeding triggers many physiological processes including post embryonic development and reproduction. Different feeding habits, such as hematophagy, can shape gene functions to meet the challenges of each type of diet. The gut of blood-sucking insects faces particular challenges after feeding due to the quantity and the quality of the food ingested. A comparison of transcriptomic and proteomic data indicates that post transcriptional regulation of gene expression is crucial in the triatomine gut. It was proposed that eukaryotic translation initiation factor 3 subunit m (eIF3m) and eIF3e define 2 different eIF3 complexes with a distinct affinity for the different mRNAs, thus selecting the set of mRNAs to be translated and constituting a post transcriptional mode of regulation of gene expression. Because the eIF3m is mainly expressed in the gut, we evaluated its relevance in Rhodnius prolixus physiology through RNA interference-mediated gene silencing. The knockdown of eIF3m reduced the digestion rate, affecting the processes triggered by a blood meal. Its silencing inhibited molting and caused premature death in nymphs while impaired ovary development, oviposition and increased resistance to starvation in adult females. The survival of males after feeding (resistance to starvation) was not affected by eIF3m knockdown. The information regarding the eIF3m function in insects is scarce and the phenotypes observed in R. prolixus upon eIF3m silencing are different and more severe than those previously described in Drosophila melanogaster, indicating a pleiotropic role of this gene in triatomines.

Phytoconstituent Profiles Associated with Relevant Antioxidant Potential and Variable Nutritive Effects of the Olive, Sweet Almond, and Black Mulberry Gemmotherapy Extracts

The extracts of whole plants or specific organs from different plant species are gaining increasing attention for their phytotherapy applications. Accordingly, we prepared standardized gemmotherapy extracts (GTEs) from young shoots/buds of olive (Olea europaea), sweet almond (Prunus amygdalus), and black mulberry (Morus nigra), and analyzed the corresponding phytonutrient profiles. We identified 42, 103, and 109 phytonutrients in the olive, almond, and black mulberry GTEs, respectively, containing amino acids, vitamins, polyphenols, flavonoids, coumarins, alkaloids, iridoids, carboxylic acids, lignans, terpenoids, and others. In order to assess the physiological effects generated by the GTEs, we developed a translational nutrition model based on Drosophila melanogaster and Cyprinus carpio. The results indicate that GTEs could influence, to a variable extent, viability and ATP synthesis, even though both are dependent on the specific carbohydrate load of the applied diet and the amino acid and polyphenol pools provided by the GTEs. It seems, therefore, likely that the complex chemical composition of the GTEs offers nutritional properties that cannot be separated from the health-promoting mechanisms that ultimately increase viability and survival. Such an approach sets the paves the way for the nutritional genomic descriptions regarding GTE-associated health-promoting effects.

Loss of Paip1 causes translation reduction and induces apoptotic cell death through ISR activation and Xrp1

Regulation of protein translation initiation is tightly associated with cell growth and survival. Here, we identify Paip1, the Drosophila homolog of the translation initiation factor PAIP1, and analyze its role during development. Through genetic analysis, we find that loss of Paip1 causes reduced protein translation and pupal lethality. Furthermore, tissue specific knockdown of Paip1 results in apoptotic cell death in the wing imaginal disc. Paip1 depletion leads to increased proteotoxic stress and activation of the integrated stress response (ISR) pathway. Mechanistically, we show that loss of Paip1 promotes phosphorylation of eIF2α via the kinase PERK, leading to apoptotic cell death. Moreover, Paip1 depletion upregulates the transcription factor gene Xrp1, which contributes to apoptotic cell death and eIF2α phosphorylation. We further show that loss of Paip1 leads to an increase in Xrp1 translation mediated by its 5'UTR. These findings uncover a novel mechanism that links translation impairment to tissue homeostasis and establish a role of ISR activation and Xrp1 in promoting cell death.

Imaging the uptake of deuterated methionine in Drosophila with stimulated Raman scattering

Introduction: Visualizing small individual biomolecules at subcellular resolution in live cells and tissues can provide valuable insights into metabolic activity in heterogeneous cells, but is challenging.

Methods: Here, we used stimulated Raman scattering (SRS) microscopy to image deuterated methionine (d-Met) incorporated into Drosophila tissues in vivo.

Results: Our results demonstrate that SRS can detect a range of previously uncharacterized cell-to-cell differences in d-Met distribution within a tissue at the subcellular level.

Discussion: These results demonstrate the potential of SRS microscopy for metabolic imaging of less abundant but important amino acids such as methionine in tissue.