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Year of Publication
Doctor of Philosophy (PhD)
Agriculture, Food and Environment
Dr. Subba Reddy Palli
Hormones are the chemical communication signaling molecules released into the body fluid to stimulate target cells of multicellular organisms. Two major hormones, ecdysteroids (20-hydroxyecdysone, 20E) and juvenile hormones (JH), regulate a wide variety of physiological and developmental processes in insects. Therefore, hormones have been extensively studied and are attractive targets for the development of target-specific insect control methods. Recent studies suggest that epigenetics adds another layer of regulation to explain multiple functions of the same circulating hormone in different tissues and at various time points. In my dissertation, I focused on a major post-translational modification, ‘acetylation,’ to elucidate the epigenetic mechanisms involved in the regulation of juvenile hormone action. Two highly conserved enzymes mediate the acetylation of histones, histone acetyltransferases (HATs) and histone deacetylases (HDACs), which mediate the addition or removal of the acetyl group to histones and other proteins.
The first part of my dissertation identified the genes coding for HDACs in Tribolium castaneum and studied their function using RNA interference (RNAi). Knockdown of 12 HDAC genes showed variable phenotypes; the most severe phenotype was detected in insects injected with double-stranded RNA (dsRNA) targeting class I (HDAC1, HDAC3) and class IV (HDAC11) HDACs. The dsHDAC1 injected larvae showed arrested growth and development and eventually died during the larval stage. The larvae injected with dsHDAC11 also showed similar phenotype as dsHDAC1 injected larvae. The knockdown of the HDAC3 gene during the final instar larval stage resulted in a pupa that showed abnormally folded wings and mortality. Application of JH analog hydroprene to the T. castaneum larvae suppressed the expression of HDAC1, HDAC3, and HDAC11 genes. Sequencing of RNA isolated from control and dsHDACs injected larvae identified several differentially expressed genes, including those involved in JH action. The acetylation levels of core histones showed an increase in TcA cells exposed to JH III or dsHDACs. Knockdown of class III ‘sirtuins deacetylase’ did not cause significant developmental defects or mortality.
The second part of my research focused on histone acetyltransferases (HATs), a superfamily of enzymes that acetylate histones and other proteins. Knockdown of four genes coding for GCN5-related N-acetyltransferases showed severe developmental defects and larval mortality. Interestingly, knockdown of an N-a-acetyltransferase, NAA40 (TC015921) induced severe developmental defects and mortality. 20E induced NAA40 expression in TcA Cells. Knockdown of NAA40 during the final instar larvae suppressed the expression of genes coding for proteins involved in ecdysone action. Overall, these data suggest that epigenetic modifications influence hormone action by modulating acetylation levels of histones and by affecting the recruitment of proteins involved in the regulation of hormone response genes.
Digital Object Identifier (DOI)
This work was supported by grants from the National Institute of Health (GM070559-13) and the National Institute of Food and Agriculture, US Department of Agriculture (HATCH project 2351177000), 2015-2019.
George, Smitha, "EPIGENETIC REGULATION OF HORMONE ACTION IN THE RED FLOUR BEETLE, TRIBOLIUM CASTANEUM (HERBST)" (2020). Theses and Dissertations--Entomology. 56.
Available for download on Tuesday, May 17, 2022