Growth, molting and regeneration in crustaceans is controlled by steroid hormones (ecdysteroids) from a pair of glands (Y-organs) in the body cavity. The Y-organs in turn are regulated by a protein hormone (MIH) from the brain. This system is comparable to human glands (testis, ovary, adrenal) that secrete steroid hormones (testosterone, estrogen, cortisone) and are controlled by protein hormones from pituitary and brain. We have found that crustaceans, like humans, make steroid hormones from cholesterol. Accordingly, we use crustacean glands as a simplified model to study how cholesterol enters cells and is converted to hormones, and how the process is regulated by the external proteins. We already know that all cholesterol in crustacean blood is bound to high-density lipoprotein (HDL), and that there are receptors on the surface of Y-organ that recognize and bind the HDL. Using radioactively labeled cholesterol and HDL, the electron microscope and the ultracentrifuge, we now will find how cholesterol enters the cells, how it is processed if still bound to HDL and where in the cells the processing takes place. Part of the study is to determine how MIH controls cholesterol entry; e.g., does MIH change the number of receptors for HDL? We will also attempt to work out the details of the biosynthesis of ecdysteroids, by using the mass spectrograph to identify the individual steps in the conversion of cholesterol to the hormones. This project embraces the fields of neurobiology, endocrinology and development in addressing basic questions on neuroendocrine coordination of functions.
