A Tale of Two States: Similarities and Differences in Neuropeptide Signaling in Larval and Adult Drosophila.

Having the life cycle divided into a larval and an adult stage, each dwelling in a separate habitat, is advantageous since it prevents competition for resources and separates development and reproduction into different stages. In holometabolous insects, larval life is characterized by intense feeding, growth, and molting, whereas the adults constitute the reproductive and highly mobile stage. This review discusses how this switch in lifestyle is reflected in the neuroendocrine system and peptidergic signaling. Neuropeptides and peptide hormones (collectively NPHs) are important regulators of most aspects of development and daily life physiology and behavior. Thus, it is of interest to understand to what extent peptidergic neurons and NPHs signaling change as the behavior and physiology alters and diversifies after metamorphosis. Focusing on larvae and adults of Drosophila melanogaster, I discuss changes in signaling in peptidergic systems. As an example, the complement of neurosecretory cells and their NPHs remain largely the same over metamorphosis, yet their functional roles change to a large extent. In larvae, many NPHs are mainly associated with regulation of development and growth, whereas in adults they regulate reproduction and complex behavior. Common to the two stages, NPHs regulate feeding, metabolism, excretion, and avoidance behavior. Other peptidergic systems, such as components of the biological clock increase drastically in complexity, both in terms of neuron types and NPHs. In summary, NPH signaling is highly flexible and individual NPHs serve multiple functions, many of which are stage specific. This review provides comprehensive descriptions of structure and function of major peptidergic systems in larvae and adults.