The role of histone locus body (HLB) assembly and the cell cycle in histone mRNA biosynthesis Public Deposited

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  • March 20, 2019
Creator
  • Terzo, Esteban
    • Affiliation: School of Medicine, Curriculum in Genetics and Molecular Biology
Abstract
  • The compartmentalization of nuclear processes such as transcription and histone mRNA biosynthesis into discrete territories is essential for orchestrating diverse gene expression programs. Genomes organize structures called nuclear bodies (NBs) that concentrate factors (proteins and RNA) required for gene expression regulation. The levels of NB components fluctuate continuously in response to diverse physiological inputs. Therefore, gaining insight into how NBs assemble and function is essential for understanding their contribution to genome function. We used the Drosophila histone locus body (HLB) to ask how HLB assembly and function contribute to replication-dependent histone gene expression. HLBs form at the histone locus and concentrate factors required for histone mRNA biosynthesis. In addition, CycE/Cdk2 is known to be required for cell cycle-dependent histone mRNA biosynthesis. We previously demonstrated that the Multi Sex Combs (Mxc) protein is required for HLB assembly and efficient histone mRNA biosynthesis and is also phosphorylated by CycE/Cdk2. However, the role that Mxc and its CycE/Cdk2-dependent phosphorylation play in HLB assembly and histone gene expression was not known. We explored the molecular mechanism by which Mxc assembles an HLB and contributes to histone gene expression, by combining biochemical assays, microscopy, and live imaging. We show that Mxc is a multivalent protein that plays an essential role in HLB assembly. We demonstrate that Mxc self-interacts, via the N-terminal LisH and the novel SIF domains, which is crucial for its accumulation at the histone locus. A region between amino acids 721 and 1481 is essential for HLB assembly independent of the LisH and SIF domains. The last 195 amino acids of Mxc are required for the recruitment of FLASH, a histone pre-mRNA processing factor, to the HLB. In addition, preliminary data suggest that Mxc harbors multiple CycE/Cdk2 phosphoepitopes required for HLB assembly. Combining the present work with our previous findings, we propose that Mxc is capable of forming a three-dimensional scaffold, the HLB, by employing multiple domains, and presumably multiple CycE/Cdk2 phosphoepitopes, to accumulate at the histone locus and to concentrate the required histone mRNA biosynthetic components to assemble a mature HLB that promotes and maintains histone gene expression throughout S phase.
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  • In Copyright
Advisor
  • Sekelsky, Jeff
  • Cook, Jean
  • Marzluff, Bill
  • Matera, Gregory
  • Duronio, Robert
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2016
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