Functional Analysis of the Role of Mcm3 in Epigenetic Gene Silencing

Project: Research

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Epigenetic gene silencing refers to inheritable repression of genes without changes in DNAsequence. Importantly, the alterations of epigenetic gene silencing are the causes of a varietyof human diseases, including loss of silencing of oncogenes in cancers and deregulatedexpression of imprinted genes in congenital human disorders. Thus, understandingmechanistically how genes are epigenetically silenced and how the repression is establishedand maintained is of great benefit to human health.X-Chromosome inactivation (XCI) is one of the classic examples of epigenetic gene silencing.It ensures the equivalent dosage of X-linked genes between XY male and XX female byrandomly silencing one of the X-chromosome in female mammals. We have previously takenXCI as a model to decipher the underlying mechanisms in maintaining gene silencing. Froma genome-wide shRNA screen, we have identified 96 candidate proteins that impact on themaintenance of inactive X-chromosome (Xi). Our ongoing work revealed an unexpected co-localizationof one of the candidates; Mcm3, with both constitutive and facultativeheterochromatin. Remarkably, the heterochromatin localization ofMcm3 is independent of itsDNA replication function. In addition, the depletion of Mcm3 resulted in elevated expressionof the repressed major satellite DNA repeats at constitutive heterochromatin. Moreover, wealso observed the reactivation of silenced GFP transgene on Xi in Mcm3 knockdown femalecells. These findings highlight the possibility that Mcm3 may play a novel and important rolein controlling gene expression via epigenetic silencing. Interestingly, recent study hasrevealed protein factor involves in XCI also regulates the expression of imprinted genes inautosomes, raising a possibility that Mcm3 may also regulates gene expression in otherbiological processes.We hypothesize that Mcm3 may have a novel role in epigenetic gene silencing and this role isindependent of its known DNA replicative helicase function. In this proposal we aim todefine this new function of Mcm3 and the molecular mechanisms by which Mcm3 regulatesgene expression in different biological processes.Our objectives are to:1) Define the role(s) ofMcm3 in the maintenance and initiation of XCI;2) Elucidate the role of Mcm3 in genomic imprinting and silencing of developmentalregulated genes;3) Characterize mechanistically how Mcm3 silences major satellite DNA repeats atconstitutive heterochromatin and genes on XCIBy completing this project, we will not only uncover the novel gene silencing function ofMcm3, but also provide new insight in understanding how different gene silencingmechanisms are regulated. Since the epigenetic silencing of tumor suppressor genes mayshare similar repression mechanisms as XCI, genomic imprinting, and/or silencing ofdevelopmental regulated genes, the knowledge gained will be translated to develop newstrategies to treat human cancers.


Project number9042165
Grant typeGRF
Effective start/end date1/01/1524/12/18