Regulatory Roles of Drosophila Insulin-Like Peptide 1 (DILP1) in Metabolism Differ in Pupal and Adult Stages

Another fly diuretic hormone: tachykinins increase fluid and ion transport by adult Drosophila melanogaster Malpighian 'renal' tubules

Insects such as the model organism Drosophila melanogaster must modulate their internal physiology to withstand changes in temperature and availability of water and food. Regulation of the excretory system by peptidergic hormones is one mechanism by which insects maintain their internal homeostasis. Tachykinins are a family of neuropeptides that have been shown to stimulate fluid secretion from the Malpighian 'renal' tubules (MTs) in some insect species, but it is unclear if that is the case in the fruit fly, D. melanogaster. A central objective of the current study was to examine the physiological role of tachykinin signaling in the MTs of adult D. melanogaster. Using the genetic toolbox available in this model organism along with in vitro and whole-animal bioassays, our results indicate that Drosophila tachykinins (DTKs) function as diuretic hormones by binding to the DTK receptor (DTKR) localized in stellate cells of the MTs. Specifically, DTK activates cation and anion transport across the stimulated MTs, which impairs their survival in response to desiccation because of their inability to conserve water. Thus, besides their previously described roles in neuromodulation of pathways controlling locomotion and food search, olfactory processing, aggression, lipid metabolism and metabolic stress, processing of noxious stimuli and hormone release, DTKs also appear to function as bona fide endocrine factors regulating the excretory system and appear essential for the maintenance of hydromineral balance.

Sex-specific regulation of development, growth and metabolism

Adult females and males of most species differ in many aspects of their morphology, physiology and behavior, in response to sex-specific selective pressures that maximize fitness. While we have an increasingly good understanding of the genetic mechanisms that initiate these differences, the sex-specific developmental trajectories that generate them are much less well understood. Here we review recent advances in the sex-specific regulation of development focusing on two models where this development is increasingly well understood: Sexual dimorphism of body size in the fruit fly Drosophila melanogaster and sexual dimorphism of horns in the horned beetle Onthophagus taurus. Because growth and development are also supported by metabolism, the regulation of sex-specific metabolism during and after development is an important aspect of the generation of female and male phenotypes. Hitherto, the study of sex-specific development has largely been independent of the study of sex-specific metabolism. Nevertheless, as we discuss in this review, recent research has begun to reveal considerable overlap in the cellular and physiological mechanisms that regulate sex-specific development and metabolism.

Genetic variation of macronutrient tolerance in Drosophila melanogaster

Carbohydrates, proteins and lipids are essential nutrients to all animals; however, closely related species, populations, and individuals can display dramatic variation in diet. Here we explore the variation in macronutrient tolerance in Drosophila melanogaster using the Drosophila genetic reference panel, a collection of ~200 strains derived from a single natural population. Our study demonstrates that D. melanogaster, often considered a "dietary generalist", displays marked genetic variation in survival on different diets, notably on high-sugar diet. Our genetic analysis and functional validation identify several regulators of macronutrient tolerance, including CG10960/GLUT8, Pkn and Eip75B. We also demonstrate a role for the JNK pathway in sugar tolerance and de novo lipogenesis. Finally, we report a role for tailless, a conserved orphan nuclear hormone receptor, in regulating sugar metabolism via insulin-like peptide secretion and sugar-responsive CCHamide-2 expression. Our study provides support for the use of nutrigenomics in the development of personalized nutrition.

Factors that regulate expression patterns of insulin-like peptides and their association with physiological and metabolic traits in Drosophila

Insulin-like peptides (ILPs) and components of the insulin signaling pathway are conserved across different animal phyla. Eight ILPs (called DILPs) and two receptors, dInR and Lgr3, have been described in Drosophila. DILPs regulate varied physiological traits including lifespan, reproduction, development, feeding behavior, stress resistance and metabolism. At the same time, different conditions such as nutrition, dietary supplements and environmental factors affect the expression of DILPs. This review focuses primarily on DILP2, DILP3, and DILP5 which are produced by insulin-producing cells in the brain of Drosophila. Although they are produced by the same cells and can potentially compensate for each other, DILP2, DILP3, and DILP5 expression may be differentially regulated at the mRNA level. Thus, we summarized available data on the conditions affecting the expression profiles of these DILPs in adult Drosophila. The accumulated data indicate that transcript levels of DILPs are determined by (a) nutritional conditions such as the protein-to-carbohydrate ratio, (b) carbohydrate type within the diet, (c) malnutrition or complete starvation; (d) environmental factors such as stress or temperature; (e) mutations of single peptides that induce changes in the expression of the other peptides; and (f) dietary supplements of drugs or natural substances. Furthermore, manipulation of specific genes in a cell- and tissue-specific manner affects mRNA levels for DILPs and, thereby, modulates various physiological traits and metabolism in Drosophila.

DIlp7-Producing Neurons Regulate Insulin-Producing Cells in Drosophila

Cellular Insulin signaling shows a remarkable high molecular and functional conservation. Insulin-producing cells respond directly to nutritional cues in circulation and receive modulatory input from connected neuronal networks. Neuronal control integrates a wide range of variables including dietary change or environmental temperature. Although it is shown that neuronal input is sufficient to regulate Insulin-producing cells, the physiological relevance of this network remains elusive. In Drosophila melanogaster, Insulin-like peptide7-producing neurons are wired with Insulin-producing cells. We found that the former cells regulate the latter to facilitate larval development at high temperatures, and to regulate systemic Insulin signaling in adults feeding on calorie-rich food lacking dietary yeast. Our results demonstrate a role for neuronal innervation of Insulin-producing cells important for fruit flies to survive unfavorable environmental conditions.

Genetic manipulation of insulin/insulin-like growth factor signaling pathway activity has sex-biased effects on Drosophila body size

In Drosophila raised in nutrient-rich conditions, female body size is approximately 30% larger than male body size due to an increased rate of growth and differential weight loss during the larval period. While the mechanisms that control this sex difference in body size remain incompletely understood, recent studies suggest that the insulin/insulin-like growth factor signaling pathway (IIS) plays a role in the sex-specific regulation of processes that influence body size during development. In larvae, IIS activity differs between the sexes, and there is evidence of sex-specific regulation of IIS ligands. Yet, we lack knowledge of how changes to IIS activity impact body size in each sex, as the majority of studies on IIS and body size use single- or mixed-sex groups of larvae and/or adult flies. The goal of our current study was to clarify the body size requirement for IIS activity in each sex. To achieve this goal, we used established genetic approaches to enhance, or inhibit, IIS activity, and quantified pupal size in males and females. Overall, genotypes that inhibited IIS activity caused a female-biased decrease in body size, whereas genotypes that augmented IIS activity caused a male-specific increase in body size. These data extend our current understanding of body size regulation by showing that most changes to IIS pathway activity have sex-biased effects, and highlights the importance of analyzing body size data according to sex.

The Role of Muscle in Insect Energy Homeostasis

Maintaining energy homeostasis is critical for ensuring proper growth and maximizing survival potential of all organisms. Here we review the role of somatic muscle in regulating energy homeostasis in insects. The muscle is not only a large consumer of energy, it also plays a crucial role in regulating metabolic signaling pathways and energy stores of the organism. We examine the metabolic pathways required to supply the muscle with energy, as well as muscle-derived signals that regulate metabolic energy homeostasis.

Network-regulated organ allometry: The developmental regulation of morphological scaling

Morphological scaling relationships, or allometries, describe how traits grow coordinately and covary among individuals in a population. The developmental regulation of scaling is essential to generate correctly proportioned adults across a range of body sizes, while the mis-regulation of scaling may result in congenital birth defects. Research over several decades has identified the developmental mechanisms that regulate the size of individual traits. Nevertheless, we still have poor understanding of how these mechanisms work together to generate correlated size variation among traits in response to environmental and genetic variation. Conceptually, morphological scaling can be generated by size-regulatory factors that act directly on multiple growing traits (trait-autonomous scaling), or indirectly via hormones produced by central endocrine organs (systemically regulated scaling), and there are a number of well-established examples of such mechanisms. There is much less evidence, however, that genetic and environmental variation actually acts on these mechanisms to generate morphological scaling in natural populations. More recent studies indicate that growing organs can themselves regulate the growth of other organs in the body. This suggests that covariation in trait size can be generated by network-regulated scaling mechanisms that respond to changes in the growth of individual traits. Testing this hypothesis, and one of the main challenges of understanding morphological scaling, requires connecting mechanisms elucidated in the laboratory with patterns of scaling observed in the natural world. This article is categorized under: Establishment of Spatial and Temporal Patterns > Regulation of Size, Proportion, and Timing Comparative Development and Evolution > Organ System Comparisons Between Species.