DNA Replication Genes Implicated in Heterochromatin Modulation

Abstract

Cellular DNA is stored compactly in the nucleus in complex with protein factors. The condensed structure or chromatin is categorized as euchromatin ‐ a relatively loose form consisting of frequently transcribed genes, and heterochromatin ‐ a denser, more compact form that covers mostly noncoding genes, transposable elements, and satellite repeats. Some of the functions of heterochromatin are: suppression of recombination of transposable elements, proper segregation of chromosomes and regulation of gene expression. Hence, heterochromatin is vital for maintaining genomic stability. Heterochromatin can be further classified as facultative (assembles and dissembles for gene expression regulation) and constitutive (condensed throughout the cell cycle). Although condensed, heterochromatin has to be unraveled during DNA replication. How does the cell know when to change heterochromatin for replication or when to return to its previous compact state? The overarching goal of this project is to understand the molecular factors that help modulate heterochromatin states to allow replication through silenced regions. Using fission yeast, we conducted a forward genetic screen with Hermes transposon as a random mutagen to obtain Position Effect Variegation (PEV) mutants of heterochromatic ade6 reporter gene. With whole genome sequencing, we identified the mutants that showed loss of silencing at the reporter gene; a number of these mutations were found to be in essential genes. Selection for loss of silencing at the pericentromeric ade6 reporter corresponded with an enrichment in mutants of DNA replication and repair genes. We hypothesize that these mutants can be recreated with CRISPR‐Cas9. The primary aim of my project is to generate mutant alleles of essential genes involved in DNA replication and repair, and validate their heterochromatin mutant phenotype. Using CRISPR ‐ Cas9 genome editing, we targeted five such genes in fission yeast: Vid21, Orc4, Cut1, Cut9, Drc1, and Dcr1 as a method control. The results we found show that we were able to generate viable mutant alleles that may be otherwise difficult to generate using conventional genetic manipulations. This study of the characterization of mutant alleles will enable us to understand their role(s) in the coordination of heterochromatin states and DNA replication and/or repair.Support or Funding InformationThis work was supported by RiSE at Rutgers, NIH grant K12GM093854‐07A1 to IRACDA at Rutgers University, NIH‐NIGMS T32 GM8339 New York for Science Partnerships in Research and Education ‐ Rutgers University Biotechnology Training Program and NIH NIGMS RO1 GM105831.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.