Genetic Molecular And Ultrastructural Characterization Of Myosin Heavy Chain Mutations In Drosophila Melanogaster PDF Download

Manipulation of muscle genes to cause their under-, over- and mis-expression and subsequent assessment of resultant phenotypes offers a comprehensive approach to understand muscle assembly, development and function. These techniques are readily applied to the fruit fly, Drosophila melanogaster, because of the relative ease of mutant isolation and germ-line transformation. The consequences of altered muscle gene expression on muscle function and ultrastructure can be well characterized in this genetic system. This dissertation describes experiments to examine the roles of two thick filament proteins and a metabolic enzyme on Drosophila muscle structure and function. In the first chapter, I have determined the genetic lesion for the Mhc2 mutant and performed detailed ultrastructural analysis of the indirect flight muscle (IFM) of mutant and transgenic lines. This investigation reveals the negative effects of over-expression and under-expression of the Mhc gene on muscle function and structure. In Chapter Two, I characterize an enhancer detection line that exhibits strong IFM specific reporter gene activity. The P element of the enhancer detection line lies downstream of the enolase gene. Two interesting complementation groups result when the P element is used to mutagenize this locus. One complementation group is the first identification of a Drosophila enolase mutant, and the other is an unknown mutation that affects flight ability presumably by disrupting mitochondrial function in the IFM. In Chapter Three, I identify both standard (PM) and mini-paramyosin (mPM) mutants. Although thick filaments are present in embryonic body-wall muscle that is lacking PM, the sarcomere is unordered, indicating that PM is needed for its normal structure and function. Low levels of mPM significantly impair flight ability and viability. In addition, more thick filaments incorporate into IFM myofibrils of the mPM mutant than those of wild-type. Over-expression of either PM or mPM affects IFM structure and function. It also appears that equivalent stoichiometric levels of mPM and PM are important for correct sarcomeric structure in the IFM. From these studies, we determine that both PM and mPM confer specific structural qualities to the thick filament and myofibril morphology.