Oxygen Dependence of Flight Performance in Ageing Drosophila melanogaster

A neural m6A pathway regulates behavioral aggregation in migratory locusts

RNA N6-methyladenosine (m6A), as the most abundant modification of messenger RNA, can modulate insect behaviors, but its specific roles in aggregation behaviors remain unexplored. Here, we conducted a comprehensive molecular and physiological characterization of the individual components of the methyltransferase and demethylase in the migratory locust Locusta migratoria. Our results demonstrated that METTL3, METTL14 and ALKBH5 were dominantly expressed in the brain and exhibited remarkable responses to crowding or isolation. The individual knockdown of methyltransferases (i.e., METTL3 and METTL14) promoted locust movement and conspecific attraction, whereas ALKBH5 knockdown induced a behavioral shift toward the solitary phase. Furthermore, global transcriptome profiles revealed that m6A modification could regulate the orchestration of gene expression to fine tune the behavioral aggregation of locusts. In summary, our in vivo characterization of the m6A functions in migratory locusts clearly demonstrated the crucial roles of the m6A pathway in effectively modulating aggregation behaviors.

How does a fly die? Insights into ageing from the pathophysiology of Drosophila mortality

The fruit fly Drosophila melanogaster is a common animal model in ageing research. Large populations of flies are used to study the impact of genetic, nutritional and pharmacological interventions on survival. However, the processes through which flies die and their relative prevalence in Drosophila populations are still comparatively unknown. Understanding the causes of death in an animal model is essential to dissect the lifespan-extending interventions that are organism- or disease-specific from those broadly applicable to ageing. Here, we review the pathophysiological processes that can lead to fly death and discuss their relation to ageing.

Heat tolerance in Drosophila melanogaster is influenced by oxygen conditions and mutations in cell size control pathways

Understanding metabolic performance limitations is key to explaining the past, present and future of life. We investigated whether heat tolerance in actively flying Drosophila melanogaster is modified by individual differences in cell size and the amount of oxygen in the environment. We used two mutants with loss-of-function mutations in cell size control associated with the target of rapamycin (TOR)/insulin pathways, showing reduced (mutant rictorΔ2) or increased (mutant Mnt1) cell size in different body tissues compared to controls. Flies were exposed to a steady increase in temperature under normoxia and hypoxia until they collapsed. The upper critical temperature decreased in response to each mutation type as well as under hypoxia. Females, which have larger cells than males, had lower heat tolerance than males. Altogether, mutations in cell cycle control pathways, differences in cell size and differences in oxygen availability affected heat tolerance, but existing theories on the roles of cell size and tissue oxygenation in metabolic performance can only partially explain our results. A better understanding of how the cellular composition of the body affects metabolism may depend on the development of research models that help separate various interfering physiological parameters from the exclusive influence of cell size. This article is part of the theme issue 'The evolutionary significance of variation in metabolic rates'.

The Drosophila melanogaster ACE2 ortholog genes are differently expressed in obesity/diabetes and aging models: Implications for COVID-19 pathology

The Spike glycoprotein of SARS-CoV-2, the virus responsible for coronavirus disease 2019, binds to its ACE2 receptor for internalization in the host cells. Elderly individuals or those with subjacent disorders, such as obesity and diabetes, are more susceptible to COVID-19 severity. Additionally, several SARS-CoV-2 variants appear to enhance the Spike-ACE2 interaction, which increases transmissibility and death. Considering that the fruit fly is a robust animal model in metabolic research and has two ACE2 orthologs, Ance and Acer, in this work, we studied the effects of two hypercaloric diets (HFD and HSD) and aging on ACE2 orthologs mRNA expression levels in Drosophila melanogaster. To complement our work, we analyzed the predicted binding affinity between the Spike protein with Ance and Acer. We show for the first time that Ance and Acer genes are differentially regulated and dependent on diet and age in adult flies. At the molecular level, Ance and Acer proteins exhibit the potential to bind to the Spike protein in different regions, as shown by a molecular docking approach. Acer, in particular, interacts with the Spike protein in the same region as in humans. Overall, we suggest that the D. melanogaster is a promising animal model for translational studies on COVID-19 associated risk factors and ACE2.

Measuring the repertoire of age-related behavioral changes in Drosophila melanogaster

Aging affects almost all aspects of an organism—its morphology, its physiology, its behavior. Isolating which biological mechanisms are regulating these changes, however, has proven difficult, potentially due to our inability to characterize the full repertoire of an animal’s behavior across the lifespan. Using data from fruit flies (D. melanogaster) we measure the full repertoire of behaviors as a function of age. We observe a sexually dimorphic pattern of changes in the behavioral repertoire during aging. Although the stereotypy of the behaviors and the complexity of the repertoire overall remains relatively unchanged, we find evidence that the observed alterations in behavior can be explained by changing the fly’s overall energy budget, suggesting potential connections between metabolism, aging, and behavior.

Aging is a ubiquitous biological phenomenon that affects many aspects of an animal’s appearance, physiology, and behavior. Our understanding of how changes in physiology lead to behavioral changes, however, has been partially limited by our ability to robustly quantify how behavior alters over timescales of days and weeks. In this study, we measure a large repertoire of behaviors of fruit flies at various ages, finding how the actions the animals perform shift with age. We observe a difference between the aging dynamics of male and female flies, and we show that many of these changes can be explained with a model of energy consumption, leading us to make predictions as to the role of metabolism in changes in aging behavior.

Thermal and Oxygen Flight Sensitivity in Ageing Drosophila melanogaster Flies: Links to Rapamycin-Induced Cell Size Changes

Simple Summary

Cold-blooded organisms can become physiologically challenged when performing highly oxygen-demanding activities (e.g., flight) across different thermal and oxygen environmental conditions. We explored whether this challenge decreases if an organism is built of smaller cells. This is because small cells create a large cell surface, which is costly, but can ease the delivery of oxygen to cells’ power plants, called mitochondria. We developed fruit flies in either standard food or food with rapamycin (a human drug altering the cell cycle and ageing), which produced flies with either large cells (no supplementation) or small cells (rapamycin supplementation). We measured the maximum speed at which flies were flapping their wings in warm and hot conditions, combined with either normal or reduced air oxygen concentrations. Flight intensity increased with temperature, and it was reduced by poor oxygen conditions, indicating limitations of flying insects by oxygen supply. Nevertheless, flies with small cells showed lower limitations, only slowing down their wing flapping in low oxygen in the hot environment. Our study suggests that small cells in a body can help cold-blooded organisms maintain demanding activities (e.g., flight), even in poor oxygen conditions, but this advantage can depend on body temperature.

Abstract

Ectotherms can become physiologically challenged when performing oxygen-demanding activities (e.g., flight) across differing environmental conditions, specifically temperature and oxygen levels. Achieving a balance between oxygen supply and demand can also depend on the cellular composition of organs, which either evolves or changes plastically in nature; however, this hypothesis has rarely been examined, especially in tracheated flying insects. The relatively large cell membrane area of small cells should increase the rates of oxygen and nutrient fluxes in cells; however, it does also increase the costs of cell membrane maintenance. To address the effects of cell size on flying insects, we measured the wing-beat frequency in two cell-size phenotypes of Drosophila melanogaster when flies were exposed to two temperatures (warm/hot) combined with two oxygen conditions (normoxia/hypoxia). The cell-size phenotypes were induced by rearing 15 isolines on either standard food (large cells) or rapamycin-enriched food (small cells). Rapamycin supplementation (downregulation of TOR activity) produced smaller flies with smaller wing epidermal cells. Flies generally flapped their wings at a slower rate in cooler (warm treatment) and less-oxygenated (hypoxia) conditions, but the small-cell-phenotype flies were less prone to oxygen limitation than the large-cell-phenotype flies and did not respond to the different oxygen conditions under the warm treatment. We suggest that ectotherms with small-cell life strategies can maintain physiologically demanding activities (e.g., flight) when challenged by oxygen-poor conditions, but this advantage may depend on the correspondence among body temperatures, acclimation temperatures and physiological thermal limits.