Molecular physiology of crustacean and insect neuropeptides (original) (raw)

2007, Journal of Pesticide Science

One of the principal hallmarks of a living organism is its ability to respond to stimuli. As the unicellular organisms evolved into multicellular metazoans, the external signals perceived had to be transduced to several other cells requiring a neuronal network with its accompanying biochemical neurotransmitters. The progressive increase in complexity of the organisms necessitated the need for an integrated signal transducing system collecting external sensory stimuli and sending them to effector systems such that a dynamic equilibrium or homeostasis, which is essential for survival, could be maintained. During the course of evolution many advanced sense organs were developed to detect various parameters in the environment, and concomitantly different internal effector systems were formed to respond to these signals received from outside to maintain homeostasis. Coordination was achieved with a network of electrical conductors in the form of an arborized nervous system and a variety of hydrophilic biochemicals that acted as neurotransmitters carrying the sensory signals to the internal effector systems. As the animal became increasingly complex, a sophisticated neurotransmission system catering to the spatial and temporal needs during growth, development and reproduction had to be in place. Parts of the nervous tissue in many locations took on a secretory role and released protein signal transducers, the neuropeptides. A panoply of such neuropeptides exist in all organisms functioning as neurohormones, neurotransmitters or neuromodulators. Aspects of neuropeptide structure and function in insects and crustaceans have been reviewed by various authors. 1-10) The neuropeptides are ligands to their cognate receptors in the ef-Organisms have to constantly respond to environmental conditions to maintain a status of dynamic homeostasis for survival. As single celled organisms evolved into multicellular animals, intercellular and inter-organ communications became indispensable not only to orchestrate homeostasis but also to control the many events punctuating metazoan development. To accomplish this need, a signal transduction system was evolved, consisting of an arborized network of nerves as well as a collection of oligopeptide neurotransmitters (neuropeptides) along with their cognate receptors. We review here the current state of our understanding of the physiology of neuropeptides in the most species-rich group of animals, the crustaceans and insects. The vast majority of neuropeptides signal through cell-surface guanosine-protein coupled receptors (GPCRs). These neuropeptide-receptor systems control a variety of physiological functions, for instance the numerous involuntary movements of internal ducts that are precisely timed for transporting reproductive, digestive and secretory materials. The rigid exoskeleton in Crustaceans and Insects require periodic molts to accomplish growth and metamorphosis and this is harmoniously regulated by a cascade of neuropeptides. Neuropeptides also regulate various events in the life of organisms including biological clocks and behavior. Technological advances in peptidomics, through the routine use MALDI-TOF mass spectrometry and in genomics, with in silico identification of neuropeptide receptor genes have revealed a staggering diversity of extracellular peptide-based signaling systems. This diversity underscores that communication between the afferent (nervous) system and the appropriate organs for an efferent response must be done in an unambiguous manner without any short circuits or reversal of directions. While we have a broad understanding of how neuropeptides and their receptors play a vital role in signal transduction, much of the details remain to be unraveled.