Growth Regulation Through Insulin-Like Peptides During Insect Development

Proper growth regulation in animals ensures species-specific body and organ sizes, with nutrition being the most significant environmental factor influencing growth. In insects, insulin-like peptides (ILPs), structurally similar to vertebrate insulin superfamily peptides, mediate nutrient-dependent growth. Most ILPs activate the insulin/insulin-like growth factor (IGF) signaling (IIS) pathway via insulin-like receptors (InR) to promote systemic and tissue growth. In insects, the primary source of ILPs is the medial neurosecretory cells (mNSCs) in the brain, where ILP expression and secretion are tightly controlled by nutritional status through multiple mechanisms. Various factors that regulate ILP expression and secretion have been identified using tissue- and cell-specific genetic tools in the fruit fly Drosophila melanogaster. ILP activity is further modulated by ILP-binding proteins, which control ILP availability and receptor binding, fine-tuning the IIS pathway. Organ-specific growth regulation is achieved through differences in IIS sensitivity. These differences in sensitivity allow precise control of organ size in response to nutritional and environmental fluctuations, emphasizing the evolutionary adaptability of the IIS pathway to adjust growth to environmental demands. In conclusion, ILPs play a central role in integrating nutritional signals to regulate systemic and organ-specific growth during insect development.