Neurohormones are responsible for controlling different aspects of physiology and behavior including body growth, eating, drinking, and sex and reproduction. The broad goal of this project is to understand cellular mechanisms controlling synthesis of a neuropeptide hormone using neurons that control reproduction in the mollusk Aplysia. Earlier studies from the PI's laboratory showed that electrical excitation of the reproductive neuroendocrine bag-cell neurons (BCNs) led to large amounts of secretion of the neuropeptide egg-laying hormone (ELH). It was revealed that electrical excitation upregulates ELH synthesis to replenish releasable stores of hormone by both sodium- and calcium-dependent pathways that are independent from both ELH secretion and action potential firing. Furthermore, a novel protein-synthetic pathway involving a special code on ELH mRNA called an internal ribosomal entry site (IRES) plays an important role in mediating the effects of electrical excitation on upregulating specifically ELH synthesis, at the expense of non-essential proteins in the cell. This is similar to how viruses control protein synthesis in cells following infection, and was not thought to play a physiological role in cellular systems. The aim of this project is to understand the mechanistic links between membrane electrical excitation, sodium/calcium ion fluxes into the bag cell neurons, IRES activation on ELH mRNA, and ELH synthesis. Experiments will utilize electrophysiological monitoring of membrane electrical excitability and optical imaging of intracellular calcium concentrations in response to treatments that alter sodium/calcium flux, biochemical measurement of ELH synthesis, and a combination of molecular biological tools and optical imaging to monitor IRES activation in living bag cell neurons in the intact Aplysia nervous tissue. The outcome from the proposed experiments will lead to entirely novel conclusions regarding the control of specific protein synthesis in cells. This project provides excellent training opportunities for graduate and undergraduate students embarking on cutting-edge studies using an integrative experimental approach
