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Mutants in the Drosophila InsP3R gene (itpr) are flight defective. Expression of the wild-type InsP3R in aminergic interneurons rescues flight. However, molecular and cellular changes in the central nervous system of InsP3R mutants that lead to flightless behavior remain unknown. To understand the molecular basis of flight phenotypes in Drosophila InsP3R mutants a microarray screen was done with RNA isolated from adult heads and thoraces. We found down-regulation of several genes that affect the excitability of neurons and muscles. Among these the role of glutamine synthetase 2 was investigated further. This enzyme reduces glutamate levels at the synapse. Our results show that Gs2 (glutamine synthetase 2) transcripts and glutamate levels correspond precisely but inversely, with InsP3R phenotypes, which can be rescued by a mutant allele for Gs2, namely, Gs2(m13). From measuring axonal branches and synapse number at a glutamatergic synapse--the adult flight neuromuscular junction--of InsP3R mutants, we conclude that glutamate homeostasis is altered through a cell non-autonomous mechanism, and is likely to be an important basis for the observed flight defects.

Ionic Ca2+ functions as a second messenger to control several intracellular processes. It also influences intercellular communication. The release of Ca2+ from intracellular stores through the inositol 1,4,5-trisphosphate receptor (InsP3R) occurs in both excitable and nonexcitable cells. In Drosophila, InsP3R activity is required in aminergic interneurons during pupal development for normal flight behavior. By altering intracellular Ca2+ and InsP3 levels through genetic means, we now show that signaling through the InsP3R is required at multiple steps for generating the neural circuit required in air puff-stimulated Drosophila flight. Decreased Ca2+ release in aminergic neurons during development of the flight circuit can be compensated by reducing Ca2+ uptake from the cytosol to intracellular stores. However, this mode of increasing intracellular Ca2+ is insufficient for maintenance of flight patterns over time periods necessary for normal flight. Our study suggests that processes such as maintenance of wing posture and formation of the flight circuit require InsP3 receptor function at a slow timescale and can thus be modulated by altering levels of cytosolic Ca2+ and InsP3. In contrast, maintenance of flight patterns probably requires fast modulation of Ca2+ levels, in which the intrinsic properties of the InsP3R play a pivotal role.

The discovery of human obesity-associated genes can reveal new mechanisms to target for weight loss therapy. Genetic studies of obese individuals and the analysis of rare genetic variants can identify novel obesity-associated genes. However, establishing a functional relationship between these candidate genes and adiposity remains a significant challenge. We uncovered a large number of rare homozygous gene variants by exome sequencing of severely obese children, including those from consanguineous families. By assessing the function of these genes in vivo in Drosophila, we identified 4 genes, not previously linked to human obesity, that regulate adiposity (itpr, dachsous, calpA, and sdk). Dachsous is a transmembrane protein upstream of the Hippo signalling pathway. We found that 3 further members of the Hippo pathway, fat, four-jointed, and hippo, also regulate adiposity and that they act in neurons, rather than in adipose tissue (fat body). Screening Hippo pathway genes in larger human cohorts revealed rare variants in TAOK2 associated with human obesity. Knockdown of Drosophila tao increased adiposity in vivo demonstrating the strength of our approach in predicting novel human obesity genes and signalling pathways and their site of action. This study set out to identify novel gene variants that may contribute to human obesity, by combining human exosome sequencing analyses with systematic functional screening in Drosophila. This identifies a number of novel obesity-associated genes which control adiposity in flies, and uncovers a potential role for the Hippo signaling pathway in obesity. [ABSTRACT FROM AUTHOR]

Calcium (Ca2+) signaling is known to regulate the development, maintenance and modulation of activity in neuronal circuits that underlie organismal behavior. In Drosophila, intracellular Ca2+ signaling by the inositol 1,4,5-trisphosphate receptor and the storeoperated channel (dOrai) regulates the formation and function of neuronal circuits that control flight. Here, we show that restoring InsP3R activity in insulin-producing neurons of flightless InsP3R mutants (itpr) during pupal development can rescue systemic flight ability. Expression of the store operated Ca2+ entry (SOCE) regulator dSTIM in insulin-producing neurons also suppresses compromised flight ability of InsP3R mutants suggesting that SOCE can compensate for impaired InsP3R function. Despite restricted expression of wild-type InsP3R and dSTIM in insulin-producing neurons, a global restoration of SOCE and store Ca2+ is observed in primary neuronal cultures from the itpr mutant. These results suggest that restoring InsP3R-mediated Ca2+ release and SOCE in a limited subset of neuromodulatory cells can influence systemic behaviors such as flight by regulating intracellular Ca2+homeostasis in a large population of neurons through a non-cell-autonomous mechanism. [ABSTRACT FROM AUTHOR]

Animals adapt their growth rate and body size to available nutrients by a general modulation of insulin–insulin-like growth factor signaling. In Drosophila, dietary amino acids promote the release in the hemolymph of brain insulin-like peptides (Dilps), which in turn activate systemic organ growth. Dilp secretion by insulin-producing cells involves a relay through unknown cytokines produced by fat cells. Here, we identify Methuselah (Mth) as a secretin-incretin receptor subfamily member required in the insulin-producing cells for proper nutrient coupling. We further show, using genetic and ex vivo organ culture experiments, that the Mth ligand Stunted (Sun) is a circulating insulinotropic peptide produced by fat cells. Therefore, Sun and Mth define a new cross-organ circuitry that modulates physiological insulin levels in response to nutrients. [ABSTRACT FROM AUTHOR]