Function and regulation of nitric oxide signaling in Drosophila.

Nitric oxide (NO) serves as an evolutionarily conserved signaling molecule that plays an important role in a wide variety of cellular processes. Extensive studies in Drosophila melanogaster have revealed that NO signaling is required for development, physiology, and stress responses in many different types of cells. In neuronal cells, multiple NO signaling pathways appear to operate in different combinations to regulate learning and memory formation, synaptic transmission, selective synaptic connections, axon degeneration, and axon regrowth. During organ development, elevated NO signaling suppresses cell cycle progression, whereas downregulated NO leads to an increase in larval body size via modulation of hormone signaling. The most striking feature of the Drosophila NO synthase is that various stressors, such as neuropeptides, aberrant proteins, hypoxia, bacterial infection, and mechanical injury, can activate Drosophila NO synthase, initially regulating cellular physiology to enable cells to survive. However, under severe stress or pathophysiological conditions, high levels of NO promote regulated cell death and the development of neurodegenerative diseases. In this review, I highlight and discuss the current understanding of molecular mechanisms by which NO signaling regulates distinct cellular functions and behaviors.