In development, changes in gene expression patterns define cell identity. These specific gene expression patterns are established at early embryonic stages, and must be passed on to daughter cells after cell division, a process termed epigenetic maintenance. The underlying mechanisms are achieved by the highly conserved trithorax-group (trxG) and Polycomb-group (PcG) proteins, which are responsible for the maintenance of transcriptional activation and repression, respectively, of numerous target genes. The roles of these proteins in transcription remain obscure, and the way they pass epigenetic information during the cell cycle is completely unknown. We found that trxG proteins are essential for transcriptional elongation. We also found that during DNA replication several trxG and PcG proteins remain stably associated with their binding sites on DNA in vivo. The goal of this proposal is to test two hypotheses: (1) that establishment of epigenetic maintenance is achieved by the complex interactions between trxG and PcG proteins;and (2) once the status of gene expression is determined, these proteins serve as epigenetic marks during the cell cycle to pass this information to daughter cells. To test the first hypothesis, we developed a technique that allows biochemical analysis of the chromatin composition of the trxG-activated and the PcG-silenced Hox target gene Ultrabithorax at very early blastoderm stages of embryo development. During these stages epigenetic maintenance is being established. Using this technique, we propose to address the following questions: (i) What is the role of PcG proteins in transcriptional repression during the establishment and maintenance of epigenetic transcription status in vivo? (ii) What are the molecular differences between active and silenced Ubx during establishment and maintenance phases? (iii) Do the opposing groups of regulators act antagonistically or independently? To test our second hypothesis, we developed a new in vivo approach to examine association of chromosomal proteins and histones with specific chromatin domains during DNA replication. This approach will be used to (iv) test the hypothesis that trxG and PcG proteins are essential epigenetic marks in re-establishing chromatin domains of the target gene following DNA replication. Given conservation of the function of trxG and PcG proteins in higher eukaryotes, these studies will greatly advance our knowledge of the basic mechanisms of transcriptional regulation and epigenetic inheritance and their relevance to diseases like cancer.

Public Health Relevance

The epigenetic program that determines the status of gene expression in a particular part of the body is established very early during embryo development, and any perturbations in this program may lead to death or diseases, like cancer. Once this program is established, the state of gene activity in each cell has to be faithfully inherited in daughter cells.
The aim of this project is to understand the mechanisms that underline the regulatory events that are essential for the establishment, maintenance and inheritance of these epigenetic programs in embryogenesis.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Development - 2 Study Section (DEV2)
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Carter, Anthony D
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Thomas Jefferson University
Schools of Medicine
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Petruk, Svetlana; Cai, Jingli; Sussman, Robyn et al. (2017) Delayed Accumulation of H3K27me3 on Nascent DNA Is Essential for Recruitment of Transcription Factors at Early Stages of Stem Cell Differentiation. Mol Cell 66:247-257.e5
Akishina, Angelina A; Vorontsova, Julia E; Cherezov, Roman O et al. (2017) Xenobiotic-induced activation of human aryl hydrocarbon receptor target genes in Drosophila is mediated by the epigenetic chromatin modifiers. Oncotarget 8:102934-102947
Petruk, Svetlana; Mariani, Samanta A; De Dominici, Marco et al. (2017) Structure of Nascent Chromatin Is Essential for Hematopoietic Lineage Specification. Cell Rep 19:295-306
Petruk, Svetlana; Fenstermaker, Tyler K; Black, Kathryn L et al. (2016) Detection of RNA-DNA association by a proximity ligation-based method. Sci Rep 6:27313
L Black, Kathryn; Petruk, Svetlana; Fenstermaker, Tyler K et al. (2016) Chromatin proteins and RNA are associated with DNA during all phases of mitosis. Cell Discov 2:16038
Petruk, Svetlana; Black, Kathryn L; Kovermann, Sina K et al. (2013) Stepwise histone modifications are mediated by multiple enzymes that rapidly associate with nascent DNA during replication. Nat Commun 4:2841
Petruk, Svetlana; Sedkov, Yurii; Johnston, Danika M et al. (2012) TrxG and PcG proteins but not methylated histones remain associated with DNA through replication. Cell 150:922-33
Orlovsky, Kira; Kalinkovich, Alexander; Rozovskaia, Tanya et al. (2011) Down-regulation of homeobox genes MEIS1 and HOXA in MLL-rearranged acute leukemia impairs engraftment and reduces proliferation. Proc Natl Acad Sci U S A 108:7956-61
Johnston, Danika M; Sedkov, Yurii; Petruk, Svetlana et al. (2011) Ecdysone- and NO-mediated gene regulation by competing EcR/Usp and E75A nuclear receptors during Drosophila development. Mol Cell 44:51-61
Petruk, Svetlana; Smith, Sheryl T; Sedkov, Yurii et al. (2008) Association of trxG and PcG proteins with the bxd maintenance element depends on transcriptional activity. Development 135:2383-90

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