| Aging can be defined as a time-dependent, gradual and detrimental change in the structure and physiological function of an organism, ultimately leading to death. Aging is a complex process involving hereditary, environmental and life style factors. Factors that influence the aging process must change the longevity. Studies aimed at determining the molecular basis of aging have revealed that genes influencing longevity are involved in a wide variety of molecular processes ranging from the metabolism of reactive oxygen species (ROS) to protein repair. Therefore, cumulative damages to macromolecules induced by ROS may be responsible for loss of important cellular functions and hence for cell decline during aging.According to the free radical theory of aging, lifespan is determined by the ability of organisms to cope with random somatic damages induced by reactive oxygen species and the natural by-products of energy metabolism. Among the affected molecules are proteins that can be chemically modified during the aging process. Accordingly, preventing damages such as those induced by mitochondrial ROS should protect against aging and extend lifespan. Heat shock proteins (Hsps) are molecular chaperones that are coordinately expressed following stress and have been shown to be major determinants in the acquisition of thermotolerance and stress resistance. The Hsps are members of a larger group of proteins called molecular chaperones, characterized by their ability to affect the structure or folded state of other proteins.Drosophila hsp22 RNA and protein were found to be induced during aging. The dramatic induction of Drosophila hsp22 RNA during aging so far appears to be a novel pattern of gene expression in higher eukaryotes, where specific gene expression patterns have been analyzed and often found to be constant or to decrease with age.The acetylation and deacetylation of histones in nucleosomes play an important role in regulating gene expression. Post-translational acetylationof the specific lysine resides in the amino terminals of histones by histone acetyltransferases (HATs) is thought to neutralize the positive charge, thus, generate a more open DNA conformation to allow the access of transcription factors on the target genes. Deacetylation of histones by HDACs, on the other hand, restores the positive charges on histones by removing the acetyl groups and leads to condensation of the nucleosome structure. Hyperacetylated histones are linked to transcriptionally active domains, whereas hypoacetylated histones are generally associated with transcriptionally silent loci.The level of acetylation is related to the longevity of animals. How the acetylation and deacetylation affect longevity, however, remains obscure. SIR2 and RPD3 are both HDACs, yet deletion of sir2 shortens lifespan while rpd3 knock out increases lifespan in Saccharomyces cerevisiae. Furthermore, overexpression of SIR2 extends the budding yeast lifespan.In this study, we investigated the influences of histone acetylation modification on the expression of hsp22 gene and on the longevity in Drosophila melanogaster, by using histone deacetylase (HDAC) inhibitor Trichostatin A (TSA). The results showed that TSA was able to extend the lifespan of Drosophila melanogaster. Furthermore, TSA significantly promoted the hsp22 gene expression, and affected the chromatin morphology at the locus of hsp22 gene along the polytene chromosome. Data presented in this study implicate that TSA may affect the longevity of Drosophila through changing the level of histone acetylation and hence influencing the expression of hsp22 gene that is related to aging and longevity.
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