Combinatorial histone modifications control chromatin packaging which in turn, contributes to the precise patterning of gene expression during development. Histone acetyltransferases (HATs) are a key class of chromatin regulatory proteins that mediate such developmental chromatin control; however their specific roles during multicellular development remain unclear. Here, we report the first isolation and developmental characterization of a Drosophila HAT gene (Dmel\TIP60) that is the homolog of the human HAT gene TIP60. We show that Dmel\TIP60 is differentially expressed during Drosophila development, with transcript levels significantly peaking during embryogenesis. We further demonstrate that reducing endogenous Dmel\TIP60 expression in Drosophila embryonic cells by RNAi results in cellular defects and lethality. Finally, we use our Drosophila GAL4 inducible Dmel\TIP60 knockdown/overexpression system to explore the role of Dmel\TIP60 in a wide variety of specific tissues during Drosophila development. We show that ubiquitous and cell/tissue specific reduction of Dmel\TIP60 expression results in lethality and/or cell/tissue specific phenotypes during fly development. Loss of Dmel\TIP60 in the wing leads to a range of wing abnormalities, including the formation of wing blisters in the most severe cases. Wing surface area and cell count/hair density assays reveal that although the number of cells that compose the wing remain unaffected, their size is significantly smaller than normal and there are defects in wing cell planer polarity. Additionally, we find that loss of Dmel\TIP60 in the CNS leads to lethality and a substantial loss of differentiated neurons in the larval brain, while cyclin E levels and apoptosis remain unaffected. Finally, we show that loss of Dmel\TIP60 in the mesoderm leads to lethality, and malformation or absence of the muscle fibers in the developing embryo. Overexpression of Dmel\TIP60 in each of these tissues has no affect on their development. Taken together, our results support an essential role for Dmel\TIP60 in the differentiation and formation of a variety of specific cell and tissue types. Significantly, our inducible and targeted HAT knockdown system in Drosophila now provides a powerful tool to effectively study the roles of these chromatin mediators in specific tissues and cell types during development.Ph.D., Biology -- Drexel University, 200
