Recent advances in nutrient sensing and endocrine regulation of insect growth and development

Regulation of proper growth across the whole body and within individual organs is fundamental for animals to achieve species-specific body size and proportions, which are crucial for maximizing fitness. To accomplish this, animals continuously sense changes in both environmental and internal conditions through specific cells and organs and adjust their growth to maximize their final size while minimizing developmental time, normally via endocrine signaling. Among environmental factors, nutrition is one of the most critical determinants of development. Because macronutrients are essential for growth, insects monitor both food quality and internal nutrient concentrations to adjust their growth and developmental timing through multiple endocrine factors. In insects, growth rate is primarily regulated by insulin-like peptides, functional and structural homologs of vertebrate insulin-superfamily peptides, and their receptor, insulin-like receptor. In contrast, growth duration is mainly controlled by the steroid molting hormone ecdysone and its nuclear hormone receptor, Ecdysone receptor. In addition to ecdysone, juvenile hormone, a sesquiterpenoid hormone that acts through its own nuclear receptor, Methoprene-tolerant, modulates the action of ecdysone and thereby influences both growth rate and duration. Recent studies have revealed that several cells and organs monitor both nutrient quality and internal macronutrient levels and release a variety of hormones and cytokines that fine-tune the production and secretion of the central growth-regulating hormones. This review summarizes recent advances in our understanding of how macronutrient-sensitive endocrine pathways coordinate appropriate growth and development in insects.