Biology subjects

Mirth, C. K.

Publications and source records attributed to Mirth, C. K..

15 recordsLinked to original sources

bioRxiv2026

Genetic Variation in Organ System Decline Across the Drosophila Genetics Reference Panel

Genetic background has a significant impact on an organism's lifespan. Underlying this metric, ageing is characterised by a sequence of physiological systems decline that leads to death. Despite this, much of the ageing research performed on model organisms in the lab uses lifespan, rather than physiological decline, as a metric to measure ageing. Here, we sought to establish if differing genotype alters age-related organ system decline by repeatedly measuring the function of five organ systems throughout the lifespan of 19 lines from the Drosophila Genetic Reference Panel. We found that the magnitude of each organ system's decline differs across genotypes, and that different organ systems decline at different rates within a genotype. We also uncovered that while declines in activity rate and reproduction were associated with length of life, overall patterns of phenotypic organ system decline differed significantly across genotypes. Overall, these data suggest that individuals with different genetic backgrounds have distinct patterns of physiological decline, implying that the mechanisms driving ageing vary between individuals. These data underscore the importance of studying organ systems decline in addition to lifespan to gain a full understanding of ageing.

genetics↗

bioRxiv2025

Insulin-like peptides play distinct roles in nutrient-dependent plasticity in Drosophila

The highly conserved insulin signalling pathway regulates growth and development time in response to nutrition across metazoans. The fruit fly, Drosophila melanogaster has eight insulin-like peptides, which are differentially expressed across development time, organs, and with nutritional conditions. However, whether individual insulin-like peptides play specific roles in controlling growth remains unknown. Recent studies have revealed that the ratio of protein to carbohydrates in the diet plays a key role in regulating life history traits, rather than the total caloric content of the diet alone. Furthermore, individual insulin-like peptides vary in their expression profiles according to nutrient conditions. Whether these differences in expression have any functional significance to animal life history traits remains unclear. Here we report that reducing the protein content of the larval diet through macronutrient restriction - where the calories lost from protein dilution are offset by increased carbohydrate content - results in a more pronounced developmental delay compared to caloric restriction - where both protein and carbohydrate concentrations are reduced. We further reveal that these two diet types result in notable differences in the expression levels of Drosophila insulin-like peptides 2, 3 and 5, and observe distinct phenotypic responses of individual insulin-like peptide mutants raised on each diet type. Taken together, our findings highlight the distinct roles of individual insulin-like peptides in regulating growth and development time in response to changes in dietary macronutrients, and provide key insights into the molecular mechanisms controlling nutritional plasticity in Drosophila. ARTICLE SUMMARYThe insulin signaling pathway regulates growth and development in response to nutrition across metazoans. In the fruit fly, Drosophila melanogaster, seven insulin-like peptides have been identified that bind to a single insulin receptor, however their specific roles remain unclear. This study shows that reducing the protein content of the diet in different ways results in striking differences in the expression patterns of insulin-like peptides and different phenotypic responses of individual mutants raised on these diets. Together, these findings highlight the distinct roles insulin-like peptides play in regulating important life history traits in response to changes in dietary macronutrients.

genetics↗

bioRxiv2025

Dietary sterol depletion is associated with gut dysfunction in Drosophila melanogaster females

Recent findings have shown that dietary restriction (DR) may extend lifespan by improving late life gut health. Given that recent work has shown that micronutrients such as sterols can mediate the effects of macronutrient ratios on longevity, we decided to examine the effects of sterol limitation on gut health. We found that mothers fed low sterol diets both suffer from increased incidence of intestinal permeability and reduced lifespans. Moreover, epithelial cells in the anterior region of the guts of flies fed low sterol diets showed signs of dysfunction prematurely when compared to flies fed adequate sterols. These findings indicate that the relationship between gut dysfunction and death in D. melanogaster females is conditional on dietary sterol limitation and may point to different paths of physiological decline with ageing that depend on the precise nutritional composition of the diet.

evolutionary biology↗

bioRxiv2024

Transiently restricting individual amino acids protects D. melanogaster against multiple stressors

Nutrition and resilience are linked, though it is not yet clear how diet confers stress resistance or the breadth of stressors that it can protect against. We have previously shown that transiently restricting an essential amino acid can extend lifespan and also protect against nicotine exposure in Drosophila melanogaster, raising the possibility that amino acid restriction is geroprotective because of elevated detoxification capacity. Here, we sought to characterise the nature of this dietary mediated protection, and determine whether it was sex, amino acid, and/or nicotine specific. When we compared between sexes, we found that isoleucine deprivation increases female, but not male, nicotine resistance. Surprisingly, we found that this protection afforded to females was not replicated by dietary protein restriction and was instead specific to individual amino acid restriction. Other studies have documented methionine or leucine restriction conferring stress resistance, though we previously found that individually depriving them did not increase nicotine resistance. We therefore wondered whether reducing the severity of restriction of these amino acids could confer nicotine resistance. This was true for methionine restriction, and we found that flies fed a diet containing 25% methionine for 7 days protected against subsequent nicotine poisoning ([~]30% longer lived than controls with all amino acids). However, when dietary leucine was altered, nicotine resistance changed, but no single diet was protective. To understand whether these beneficial effects of diet were specific to nicotine or were generalisable across stressors, we pre-treated with amino acid restriction diets and exposed them to other types of stress. We did not find any diets that protected against heat stress or infection with the bacterium Enterococcus faecalis. However, we found that some of the diets that protected against nicotine also protected against oxidative and starvation stress, and improved survival following cold shock. Interestingly, we found that a diet lacking isoleucine was the only diet to protect against all these stressors. These data point to isoleucine as a critical determinant of robustness in the face of environmental challenges.

genetics↗

bioRxiv2023

Fluctuating temperatures exacerbate nutritional stress during development in Drosophila melanogaster

Recent studies suggest that elevated temperatures interact with nutrition to exacerbate the negative effects of poor nutrition. Furthermore, populations adapted to distinct environments differ in their sensitivity to combined thermal and nutritional stress. However, most studies have tested these effects using constant temperatures, even though animals in the wild experience daily and seasonal thermal fluctuations. Here, we used two locally-adapted populations of D. melanogaster from the east coast of Australia (a tropical and a temperate population) to ask whether temperature fluctuations interact with nutrition in the same manner as constant temperature conditions to shape life history traits, and how this differs across populations. We found that fluctuating temperatures exacerbate the negative effects of a poor diet when compared to constant temperatures. Moreover, the negative effects of nutritional stress were significantly greater in the tropical population. In contrast, we found that the temperate population was able to utilize nutrition in unique ways to maintain optimal viability under warmer temperatures. Our findings reveal the ways in which temperature and nutrition interact to impact key life history traits in geographically distinct populations, while also highlighting the importance of using temperature assays representative of natural diel cycles when examining insect responses to climate change.

evolutionary biology↗

bioRxiv2023

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.

molecular biology↗

bioRxiv2023

Short-term fasting of a single amino acid extends lifespan.

Diet and health are strongly linked, though the strict changes in diet required to improve health outcomes are usually difficult to sustain. We sought to understand whether short term bouts of amino acid-specific modifications to the diet of Drosophila melanogaster could mimic the lifespan and stress resistance benefits of dietary restriction, without the requirement for drastic reductions in food intake. We found that flies fed diets lacking the essential amino acid isoleucine, but otherwise nutritionally complete, exhibited enhanced nicotine tolerance, indicating elevated detoxification capacity. The protection from isoleucine deprivation increased with the duration of exposure, up to a maximum at 7-day isoleucine deprivation for flies 2, 3, or 4 weeks of age, and a 5-day deprivation when flies were 5 weeks of age. Because of these beneficial effects on toxin resistance, we intermittently deprived flies of isoleucine during the first 6 weeks of adulthood and monitored the effect on lifespan. Lifespan was significantly extended when flies experienced short term isoleucine deprivation at 3 and 5 weeks of age, regardless of whether they were also deprived at 1 week. These results indicate that short-term bouts of isoleucine deprivation can extend lifespan and highlight its cumulative and time-dependent benefits. Interestingly, we found that isoleucine-deprived flies lost their protection against nicotine within three days of returning to fully fed conditions. Therefore, the mechanisms underlying lifespan extension may involve transient damage clearance during the bouts of isoleucine deprivation rather than sustained enhanced detoxification capacity. These data highlight a new time-restricted, nutritionally precise method to extend life in Drosophila melanogaster and point to a more manageable dietary method to combat ageing.

physiology↗

bioRxiv2023

Identifying the proximate mechanisms that generate variation in nutritional plasticity for fecundity in Drosophila melanogaster

Nutrition is an important determinant of an animals survival and fitness. Phenotypic plasticity allows a genotype to adjust life history traits to changes in its nutritional environment, and it varies among individuals. To understand how variation in plasticity is achieved, we made use of a Drosophila melanogaster isogenic panel to characterize nutritional plasticity for fecundity by feeding flies diets differing in their yeast content and counting the number of eggs produced. We then identified lines with the highest and lowest plastic responses to diet and dissected the potential proximate mechanisms responsible for these differences in plasticity, including morphology, behaviour, and physiology. Our results suggest that genetic variation in plasticity is not due to differences in ovariole number, but due to both increased food intake, and higher efficiency at converting food into eggs. Our results show that, in this population of D. melanogaster, variation in behaviour and physiology, but not morphology, underlies differences in plasticity for fecundity. Further, they set the stage for future studies aiming to understand how the proximate mechanisms that generate genetic variation in plasticity contribute to a populations persistence when faced with environmental changes.

evolutionary biology↗

bioRxiv2022

Ageing impairs protein leveraging in a sex-specific manner in Drosophila melanogaster

Modifying the relative proportions of macronutrients in an animals diet has noteworthy effects on its reproduction, lifelong health, and lifespan. Because of this, a wide range of animals carefully regulate their nutrient intake toward species and stage-specific targets. However, when animals are unable to reach their nutrient target from their existing food resources, they will compromise between overconsuming one nutrient and under-consuming the deficit nutrient. In this study, we used capillary feeding (CAFE) assays to understand the rules of compromise of adult fruit flies (Drosophila melanogaster) of different sex, mating status, and age when constrained to single diets. We found that young male and female D. melanogaster compromised by consuming more food on diets with low protein to carbohydrate (P:C) ratios compared to diets with high P:C ratios. Further, young male and female flies varied their carbohydrate intake significantly more than their protein intake, and female flies varied their carbohydrate intake significantly more than males. To test for effects of mating status on nutrient intake, we compared food intake of young mated and virgin females. We found that both virgin and mated females compromised by consuming more food on the low P:C diet compared to high P:C diets; however, mated females consumed more food than virgin females. As flies aged, they decreased their overall food intake and showed more modest alterations in their food intake across varying P:C diets. Further, mated females ceased to compromise for the protein deficit at a younger age than males. These findings provide new understanding about differences in protein leveraging behaviour across sexes, and how these behaviours change with age. HighlightsO_LIYoung fruit flies exhibit protein leveraging behaviour, varying their carbohydrate consumption more than protein C_LIO_LIYoung mated female flies vary their carbohydrate consumption significantly more than young males C_LIO_LIBoth virgin and mated female flies balance their nutrient intake similarly C_LIO_LIAs flies age, their ability to protein leverage declines, and this occurs faster in female flies C_LI

animal behavior and cognition↗

bioRxiv2021

Target of Rapamycin drives unequal responses to essential amino acid depletion in egg laying

Nutrition shapes a broad range of life history traits, ultimately impacting animal fitness. A key fitness-related trait, female fecundity is well known to change as a function of diet. In particular, the availability of dietary protein is one of the main drivers of egg production, and in the absence of essential amino acids egg laying declines. However, it is unclear whether all essential amino acids have the same impact on phenotypes like fecundity. Using a holidic diet, we fed adult female D. melanogaster diets that contain all necessary nutrients except one of the 10 essential amino acids and assessed the effects on egg production. For most essential amino acids, depleting a single amino acid induced as rapid a decline in egg production as when there were no amino acids in the diet. However, when either methionine or histidine were excluded from the diet, egg production declined more slowly. Next, we tested whether GCN2 and TOR were involved in this difference in response across amino acids. While mutations in GCN2 did not eliminate the differences in the rates of decline in egg laying among amino acid drop-out diets, we found that inhibiting TOR signalling caused egg laying to decline rapidly for all drop-out diets. TOR signalling does this by regulating the yolk-forming stages of egg chamber development. Our results suggest that amino acids differ in their ability to induce signalling via the TOR pathway. This is important because if phenotypes differ in sensitivity to individual amino acids, this generates the potential for mismatches between the output of a pathway and the animals true nutritional status.

developmental biology↗

bioRxiv2020

A dietary sterol trade off determines lifespan responses to dietary restriction in Drosophila melanogaster

Diet plays a significant role in maintaining lifelong health. In particular, lowering the dietary protein : carbohydrate ratio can improve lifespan. This has been interpreted as a direct effect of these macronutrients on physiology. Using Drosophila melanogaster, we show that the role of protein and carbohydrate on lifespan is indirect, acting by altering the partitioning of limiting amounts of dietary sterols between reproduction and lifespan. Shorter lifespans in flies fed on high protein : carbohydrate diets can be rescued by supplementing their food with cholesterol. Not only does this fundamentally alter the way we interpret the mechanisms of lifespan extension by dietary restriction, these data highlight the important principle that life histories can be affected by nutrient-dependent trade-offs that are indirect and independent of the nutrients (often macronutrients) that are the focus of study. This brings us closer to understanding the mechanistic basis of dietary restriction.

evolutionary biology↗

bioRxiv2020

Insulin-like signalling influences the coordination of Drosophila larval hemocyte number with body size

Blood cells, known as hemocytes in invertebrates, play important and conserved roles in immunity, wound healing and tissue remodelling. The control of hemocyte number is therefore critical to ensure these functions are not compromised, and studies using Drosophila are proving useful for understanding how this occurs. Recently, the well characterised embryonic patterning gene, torso-like (tsl), was identified as being required both for normal hemocyte number and for providing immunity against certain pathogens. Here, we report that Tsl is required specifically during the larval phase of hematopoiesis, and that the reduced hemocyte number found in tsl mutant larvae is likely the result of a reduced larval growth rate and compromised insulin signalling. Consistent with this, we find that impairing insulin-mediated growth, either by nutrient deprivation or genetically, results in fewer hemocytes. This is likely the result of impaired insulin-like signalling in the hemocytes themselves since modulation of Insulin-like Receptor (InR) activity specifically in hemocytes causes concomitant changes to their population size in developing larvae. Taken together, our work reveals the strong relationship that exists between body size and hemocyte number, and suggests that insulin-like signalling contributes to, but is not solely responsible for, keeping these tightly aligned during larval development.

genetics↗

bioRxiv2019

When does diet matter? The roles of larval and adult nutrition in regulating adult size traits.

Adult body size is determined by the quality and quantity of nutrients available to animals. In insects, nutrition affects adult size primarily during the nymphal or larval stages. However, measures of adult size like body weight are likely to also change with adult nutrition. In this study, we sought to the roles of nutrition throughout the life cycle on adult body weight and the size of two appendages, the wing and the femur, in the fruit fly Drosophila melanogaster. We manipulated nutrition in two ways: by varying the protein to carbohydrate content of the diet, called macronutrient restriction, and by changing the caloric density of the diet, termed caloric restriction. We employed a fully factorial design to manipulate both the larval and adult diets for both diet types. We found that manipulating the larval diet had greater impacts on all measures of adult size. Further, macronutrient restriction was more detrimental to adult size than caloric restriction. For adult body weight, a rich adult diet mitigated the negative effects of poor larval nutrition for both types of diets. In contrast, small wing and femur size caused by poor larval diet could not be increased with the adult diet. Taken together, these results suggest that appendage size is fixed by the larval diet, while those related to body composition remain sensitive to adult diet. Further, our studies provide a foundation for understanding how the nutritional environment of juveniles affects how adults respond to diet.

physiology↗

bioRxiv2019

Neuropeptide F receptor acts in the Drosophila prothoracic gland to regulate growth and developmental timing

As juvenile animals grow, their behaviour, physiology, and development need to be matched to environmental conditions to ensure they survive to adulthood. However, we know little about how behaviour and physiology are integrated with development to achieve this outcome. Neuropeptides are prime candidates for achieving this due to their well-known signalling functions in controlling many aspects of behaviour, physiology and development in response to environmental cues. In the growing Drosophila larva, while several neuropeptides have been shown to regulate feeding behaviour, and a handful to regulate growth, it is unclear if any of these play a global role in coordinating feeding behaviour with developmental programs. Here, we demonstrate that Neuropeptide F Receptor (NPFR), best studied as a conserved regulator of feeding behaviour from insects to mammals, also regulates development in Drosophila. Knocking down NPFR in the prothoracic gland, which produces the steroid hormone ecdysone, generates developmental delay and an extended feeding period, resulting in increased body size. We show that these effects are due to decreased ecdysone production, as these animals have reduced expression of ecdysone biosynthesis genes and lower ecdysone titres. Moreover, these phenotypes can be rescued by feeding larvae food supplemented with ecdysone. Further, we show that NPFR negatively regulates the insulin signalling pathway in the prothoracic gland to achieve these effects. Taken together, our data demonstrate that NPFR signalling plays a key role in regulating animal development and may thus play a global role in integrating feeding behaviour and development in Drosophila.

developmental biology↗

bioRxiv2018

Torso-like is a component of the hemolymph and regulates the insulin signalling pathway in Drosophila

In Drosophila key developmental transitions are governed by the steroid hormone ecdysone. A number of neuropeptide-activated signalling pathways control ecdysone production in response to environmental signals, including the insulin signalling pathway, which regulates ecdysone production in response to nutrition. Here, we find that the Membrane Attack Complex/Perforin-like protein Torso-like, best characterised for its role in activating the Torso receptor tyrosine kinase in early embryo patterning, also regulates the insulin signalling pathway in Drosophila. We previously reported that the small body size and developmental delay phenotypes of torso-like null mutants resemble those observed when insulin signalling is reduced. Here we report that, in addition to growth defects, torso-like mutants also display metabolic and nutritional plasticity phenotypes characteristic of mutants with impaired insulin signalling. We further find that in the absence of torso-like the expression of insulin-like peptides is increased, as is their accumulation in the insulin-producing cells. Finally, we show that Torso-like is a component of the hemolymph and that it is required in the prothoracic gland to control developmental timing and body size. Taken together, our data suggest that the secretion of Torso-like from the prothoracic gland influences the activity of insulin signalling throughout the body in Drosophila.\n\nARTICLE SUMMARYIn many animals distinct developmental transitions are crucial for the coordinated progression from the juvenile stage to adulthood. In Drosophila, the transition from an immature larva into a reproductively mature adult is controlled by the steroid hormone ecdysone. Several neuropeptide-activated signalling pathways, including the insulin signalling pathway, regulate ecdysone production in response to environmental cues. Here we find that the perforin-like protein Torso-like regulates the insulin signalling pathway. We show that Torso-like is secreted into circulation where it acts to influence insulin-like peptide activity, revealing a novel mechanism for the regulation of insulin signalling in Drosophila.

developmental biology↗