Growth in crustaceans requires the periodic shedding of the shell, a process called molting, which is controlled by a neurosecretory center in the eyestalks. The complex secretes molt-inhibiting hormone (MIH) that inhibits production of the molting hormone ecdysone, an ecdysteroid secreted by a pair of molting glands (Y-organs or YOs) located in the body. Thus it appears that molting is triggered by a reduction in MIH in the blood, which stimulates the molting glands to synthesize and secrete ecdysone. It is thought that binding of MIH to a membrane receptor results in a cyclic nucleotide-dependent inhibition of ecdysone-synthesizing enzymes. Five genes were cloned in the tropical land crab that may play a role in MIH signaling: nitric oxide synthase (NOS), three guanylyl cyclases (GCs), and MIH. The specific aims of the project are to determine the MIH signal transduction pathway, determine the regulation of NOS and GCs, and determine the interaction, if any, between MIH and other related hormones.
Understanding the hormonal regulation of crustacean molting and growth is essential to manage fisheries, develop effective aquacultural practices, and mitigate potential effects of pollutants, such as endocrine disruptors. Despite intense effort, very little is known about the MIH signaling pathway. The identity of the membrane receptor and other components of the pathway remain unknown. Now that methods to express large amounts of active MIH are available, the MIH signaling pathway can be elucidated and potential interactions with other hormones and pollutants can be determined. The potential role of nitric oxide constitutes an entirely novel and exciting line of investigation. The project will train a postdoc, graduate student, and 4-6 undergraduates in advanced molecular biological techniques, including quantitative polymerase chain reaction (PCR).
