ENDOCRINE CONTROL OF FATFY ACID BINDING PROTEIN EXPRESSION IN FLIGHT MUSCLE OF SCHISTOCEKCA GREGARIA

Fatty acid binding proteins (FABPs) are abundant intracellular proteins believed to be involved in fatty acid transport and metabolism. The FABP present in flight muscle of the locust, Scizistocerca gregaria, is similar to mammalian muscle FABP in its primary structure and biochemical characteristics. The changes of locust muscle FABP concentration and distribution during development were studied using enzyme linked imrnunosorbe;lt assays and electron microscopy of irnmunogold labeled tissue secticnsLocust muscle FABP is the most abundant soluble muscle protein in fully developed adult locusts, comprising 18% of the total cytosolic protein. At the beginning of the adult stage, however, no FABP is detectable. Its concentration rises during the following 10 days, after which it reaches its maximal value. The protein is abundant in cytosol and nuclei, but virtually absent in mitochondria. The levels of FABP were examined in insects that had been treated with metamorphosis controlling hormones and anti-hormones. The FABP content was found to be similar in normal and precocious adults, but no FABP was found in last instar nymphs, methoprene induced supernumerary nymphs and azadirachtin induced over-aged nymphs. These results indicate that FABP synthesis does not occur prior to metamorphosis, but is always initiated in differentiated adult flight muscle. FABP synthesis in adult muscle, however, is not directly stimulated by any hormone from the brain or adjacent endocrine glands. FABP is expressed at high rates only at the beginning of the adult stage. In mature locusts, the protein is a major cytosolic component, but its mRNA transcription is reduced to a micimum level. In these animals, FABP gene expression can be induced by flight activity. Extended flight leads to a 15-fold increase of FABP mRNA within 16 hours; the additional synthesis of FM3P may assure a more efficient fatty acid transport towards mitochondria 13-osidatinn. Injecrion of adipokinetic hormone II (AKH 11) into resting locusts also stimulates trrinscription in a dose dependent manner. FABP mRNA reaches its m a i m u r n 16 hours after treatment and returns to its base level within 48 hours. Purified low density lipophorin, when injected into resting locusts, causes a similar increase as AKH 11 or flight, suggesting that the increased supply of fatty acid is the ultimate cause for the observed induction of FABP gene expression. Additional synthesis of FABP in response to an increase of free fatty acid in the cytosal allow> a higher fatty acid flux ~lirough the cytosol. Moreover, FABP may be necessary to protect cellular structures from damaging effects of an excess of fatty acids. My sincere thanks are due to Dr. Norbert H. Haunerland for his constant guidance and encouragement during the research for and the writing of this thesis; to Dr. Karun K. Nair for his helpful comments and suggestions; to Dr. Russell A. Nicholson for his kindness in reading my thesis and his willingness to evaluate my defence; to Dr. Victor Bourne for his technical assistance; to Mr. Akbar Syed and Mr. Marcelino Horta for tolerating my daily asking for locusts. Most of all, I thank my family: my husband, Zhixiang, for his cerebral and practical help whenever it was needed; and my parents, for writing me constantly.