Physiological and Molecular Causes of Genetic Variation/Covariation Inendocrine Regulation

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Although a tremendous amount of information is available on physiological, biochemical, and molecular aspects of endocrinology, very little is known about the evolution of endocrine regulation. Genetically-based variations in endocrine traits provide the raw material upon which natural selection acts during the initial stages of adaptive evolution. Thus, a key step in understanding the evolution of hormonal control is the characterization of genetically-based variation in endocrine regulators within species. The goal of the present multi-disciplinary study is to identify the variable molecular and physiological factors that cause genetically-based variation in the enzyme juvenile hormone esterase (JHE) in a cricket species. JHE degrades and regulates the key insect hormone, juvenile hormone, and has been the subject of intensive study in the Principal Investigator's laboratory during the past 15 years. This proposal has three primary research objectives. First, using both in vivo and in vitro approaches, the following hypothesis will be tested: genetic variation in the concentration of or tissue sensitivity to neurohormones causes genetically based variation in JHE activity and tissue distribution. Experiments will largely involve assessing the effect of extracts or implants of neural tissue derived from high- or low- JHE activity genetic stocks on JHE activity and related endocrine traits in the same vs alternate lines. Second, the role of variation in JHE messenger RNA abundance as the cause of genetically-based variation in JHE activity will be tested. JHE mRNA abundance will be compared between high and low activity lines using Northern blots employing a probe derived from a recently obtained, nearly full-length JHE cDNA. Third, the high and low JHE activity lines will be crossed and backcrossed to determine the degree of co-segregation among (1) JHE activity and associated endocrine traits, (2) molecular correlates of these traits (JHE mRNA level), and (3) potential regulators of these traits. This research will simultaneously provide important new information for several different areas of biology. This will be the first study to identify the molecular and physiological causes of genetically-based variation in an endocrine regulator in natural populations. This project will result in the first detailed synthesis of endocrine physiology, molecular biology, and quantitative genetics. Finally, these studies will constitute the first investigations of genetic variation in neuroendocrine regulation in natural populations and will set the stage for subsequent identification of these regulators and the genes that encode them.