Winant, M. | Search bioRxiv

bioRxiv2022

Genome-wide analysis identifies Homothorax and Extradenticle as regulators of insulin in Drosophila Insulin-Producing cells

Drosophila Insulin-Producing Cells (IPCs) are the main production site of the Drosophila Insulin-like peptides or Dilps which have key roles in regulating growth, development, reproduction, lifespan and metabolism. To better understand the signalling pathways and transcriptional networks that are active in the IPCs we queried publicly available transcriptome data of over 180 highly inbred fly lines for dilp expression and used this as the input for a Genome-wide association study (GWAS). This resulted in the identification of variants in 125 genes that were associated with variation in dilp expression. The function of 57 of these genes in the IPCs was tested using an RNAi-based approach. We found that IPC-specific depletion of most genes resulted in differences in expression of one or more of the dilps. We then elaborated further on homothorax, one of the candidate genes with the strongest effect on dilp expression. We found that Homothorax and its binding partner Extradenticle are involved in regulating dilp2, -3 and -5 expression and that genetic depletion of both transcription factors leads to phenotypes associated with reduced insulin signalling. Furthermore, we provide evidence that other transcription factors involved in eye development are also functional in the IPCs. In conclusion, we showed that this GWAS approach using gene expression levels as input identified genetic regulators implicated in IPC function and dilp expression.

genetics↗

bioRxiv2017

Growth control through regulation of insulin-signaling by nutrition-activated steroid hormone

Growth and maturation are coordinated processes in all animals. Integration of internal cues, such as signalling pathways, with external cues such as nutritional status is paramount for an orderly progression of development in function of growth. In Drosophila, this coordination involves insulin and steroid signalling, but the mechanisms by which this occurs and how they are coordinated are incompletely understood. We show that production of the bioactive 20-hydroxyecdysone by the enzyme Shade in the fat body is a nutrient-dependent process. We demonstrate that during fed conditions, Shade plays a role in growth regulation, as knockdown of shade in the fat body resulted in growth defects and perturbed expression and release of the Drosophila insulin-like peptides from the insulin-producing cells (IPCs). We identify the trachea and IPCs as direct targets through which 20-hydroxyecdysone regulates insulin-signaling. The identification of the trachea-dependent regulation of insulin-signaling exposes an important variable that may have been overlooked in other studies focusing on insulin-signaling in Drosophila. Finally, we show with IPC-specific manipulations that 20E may both be a growth-promoting and growth-inhibiting signal in the IPCs acting through different nuclear receptors. Our findings provide a potentially conserved, novel mechanism by which nutrition can modulate steroid hormone bioactivation, reveal an important caveat of a commonly used transgenic tool to study IPC function and yield further insights as to how steroid and insulin signalling are coordinated during development to regulate growth and developmental timing.

developmental biology↗