Natural variability in Drosophila larval and pupal NaCl tolerance

Amino Acid Substitutions in the Na + /K + -ATPase May Contribute to Salinity Tolerance in Insects

Environmental salinity levels vary naturally across terrestrial ecosystems but can be heightened locally by rising sea levels and desertification as well as human activities such as road salt application and agriculture. Since salt is essential for many physiological processes in insects, rising environmental sodium concentrations may drive behavioral changes, where insects select environments and food sources with suitable sodium levels, or evolutionary changes in constitutive or plastic physiological mechanisms to process salt, potentially altering ecological dynamics and species interactions. Numerous hematophagous (blood feeding) insects are known to breed in relatively saline environments, while others such as the yellow-fever mosquito Aedes aeqypti are expanding their range to coastal regions. Among phytophagous (plant feeding) insects, grasshoppers can be important herbivores in arid and coastal salt-affected regions, whereas the monarch butterfly ( Danaus plexippus ) appears to perform relatively well on milkweed host plants growing in roadsides influenced by salt runoff. Several of these insects share a common trait: amino acid substitutions in the first extracellular loop of the Na + /K + -ATPase (NKA), a highly conserved sodium pump crucial for maintaining ion balance. For the monarch these substitutions confer resistance to toxic cardenolides from milkweeds, but it is unclear whether NKA substitutions may influence salt tolerance. Here, we investigate whether the NKA substitutions found in these insects may contribute to salt tolerance using gene-edited Drosophila melanogaster mutant strains as models. We show that flies with the Q111L and A119S substitutions alone or in combination (found in grasshoppers and several hematophagous insects) exhibited greater salt tolerance, whereas flies carrying the combination of substitutions found in the monarch (Q111V, A119S, and N122H) did not. Our results suggest that the monarch may rely on alternate mechanisms for salt tolerance and that its NKA substitutions are important primarily for cardenolide resistance. However, substitutions Q111L and A119S may be important for salt tolerance in a variety of insects. Uncovering mechanisms of salt tolerance enhances our understanding of species distributions, ecological interactions, and evolutionary physiology in response to changing environmental salinity levels.

Optimizing food waste bioconversion with sodium selenite-enhanced Lucilia sericata maggots: a sustainable approach for chicken feed production and heavy metal mitigation

Recycling food waste by feeding it to insects can result in the continuous production of high-quality animal feed protein and organic fertilizer. However, the bioconversion efficiency and safety of using insects as feed protein for animal breeding are important factors limiting the development of this technology. Therefore, we aimed to optimize the efficiency of bioconversion of food waste using Lucilia sericata maggot (LSM). Sodium selenite (SS) was used to improve the quality and safety of each trophic-level organism. The results showed that an SS concentration of 15 mg kg-1 w.w. in the food waste culture substrate (SS15), the yield and quality of the obtained LSMs were optimal. The total selenium (Se) content of LSMs was 82.4 ± 1.16 mg kg-1 d.w., and non-inorganic Se accounted for 96.4% ± 2.01% of the total Se content. Additionally, the conversion efficiency of food waste was 18.7% higher than that in the control group (p < 0.05). When SS15 was used to raise maggots as a protein substitute for fish meal (commercial feed), the weight of the chickens and the crude protein content were 1.09-1.26 times and 1.09-1.13 times, respectively (p < 0.05), in comparison with the corresponding findings obtained with the use of ordinary maggots and commercial feed. In this group, glutathione peroxidase, superoxide dismutase, catalase, and immunoglobulin A and G activities were significantly higher than those obtained with the other feeds (p < 0.05). During this cyclic utilization process, the total Se content in chickens (0.31 ± 0.05 mg kg-1 w.w. in the breast, 0.19 ± 0.01 mg kg-1 w.w. in the leg, and 0.57 ± 0.01 mg kg-1 w.w. in the liver) significantly increased (p < 0.05). Meanwhile, the Cu and Zn contents in the LSMs and chickens increased, whereas cadmium, lead, chromium, and nickel absorption was inhibited (p < 0.05). Health risk assessment based on the levels of Se and heavy metals showed that Se-enriched chickens produced using this method can be safely consumed.

Biochemical characterization of the Drosophila insulin receptor kinase and longevity-associated mutants

Drosophila melanogaster (fruit fly) insulin receptor (D-IR) is highly homologous to the human counterpart. Like the human pathway, D-IR responds to numerous insulin-like peptides to activate cellular signals that regulate growth, development, and lipid metabolism in fruit flies. Allelic mutations in the D-IR kinase domain elevate life expectancy in fruit flies. We developed a robust heterologous expression system to express and purify wild-type and longevity-associated mutant D-IR kinase domains to investigate enzyme kinetics and substrate specificities. D-IR exhibits remarkable similarities to the human insulin receptor kinase domain but diverges in substrate preferences. We show that longevity-associated mutations reduce D-IR catalytic activity. Deletion of the unique kinase insert domain portion or mutations proximal to activating tyrosines do not influence kinase activity, suggesting their potential role in substrate recruitment and downstream signaling. Through biochemical investigations, this study enhances our comprehension of D-IR's role in Drosophila physiology, complementing genetic studies and expanding our knowledge on the catalytic functions of this conserved signaling pathway.

Transgenic expression of late embryogenesis abundant proteins improves tolerance to water stress in Drosophila melanogaster

Four lines of Drosophila melanogaster were created that expressed transgenes encoding selected late embryogenesis abundant (LEA) proteins originally identified in embryos of the anhydrobiote Artemia franciscana The overall aim was to extend our understanding of the protective properties of LEA proteins documented with isolated cells to a desiccation-sensitive organism during exposure to drying and hyperosmotic stress. Embryos of D. melanogaster were dried at 57% relative humidity to promote a loss of 80% tissue water and then rehydrated. Embryos that expressed AfrLEA2 or AfrLEA3m eclosed 2 days earlier than wild-type embryos or embryos expressing green fluorescent protein (Gal4GFP control). For the third instar larval stage, all Afrlea lines and Gal4GFP controls experienced substantial drops in survivorship as desiccation proceeded. When results for all Afrlea lines were combined, Kaplan-Meier survival curves indicated a significant improvement in survivorship in fly lines expressing AfrLEA proteins compared with Gal4GFP controls. The percent water lost at the LT₅₀ (lethal time for 50% mortality) for the AfrLEA lines was 78% versus 52% for Gal4GFP controls. Finally, offspring of fly lines that expressed AfrLEA2, AfrLEA3m or AfrLEA6 exhibited significantly greater success in reaching pupation, compared with wild-type flies, when adults were challenged with hyperosmotic stress (NaCl-fortified medium) and progeny forced to develop under these conditions. In conclusion, the gain of function studies reported here show that LEA proteins can improve tolerance to water stress in a desiccation-sensitive species that normally lacks these proteins, and, simultaneously, underscore the complexity of desiccation tolerance across multiple life stages in multicellular organisms.