Cell-cycle-regulated control of VSG expression site silencing by histones and histone chaperones ASF1A and CAF-1b in Trypanosoma brucei

Sam Alsford, David Horn

    Research output: Contribution to journalArticle

    29 Citations (Scopus)

    Abstract

    Antigenic variation in African trypanosomes involves monoallelic expression and reversible silencing of variant surface glycoprotein (VSG) genes found adjacent to telomeres in polycistronic expression sites (ESs). We assessed the impact on ES silencing of five candidate essential chromatin-associated factors that emerged from a genome-wide RNA interference viability screen. Using this approach, we demonstrate roles in VSG ES silencing for two histone chaperones. Defects in S-phase progression in cells depleted for histone H3, or either chaperone, highlight in particular the link between chromatin assembly and DNA replication control. S-phase checkpoint arrest was incomplete, however, allowing G(2)/M-specific VSG ES derepression following knockdown of histone H3. In striking contrast, knockdown of anti-silencing factor 1A (ASF1A) allowed for derepression at all cell cycle stages, whereas knockdown of chromatin assembly factor 1b (CAF-1b) revealed derepression predominantly in S-phase and G(2)/M. Our results support a central role for chromatin in maintaining VSG ES silencing. ASF1A and CAF-1b appear to play constitutive and DNA replication-dependent roles, respectively, in the recycling and assembly of chromatin. Defects in these functions typically lead to arrest in S-phase but defective cells can also progress through the cell cycle leading to nucleosome depletion and derepression of telomeric VSG ESs.

    Original languageEnglish
    Pages (from-to)10150-10160
    Number of pages11
    JournalNucleic Acids Research
    Volume40
    Issue number20
    DOIs
    Publication statusPublished - Nov 2012

    Keywords

    • S-PHASE PROGRESSION
    • NUCLEOSOMES
    • GENE-EXPRESSION
    • DNA-REPLICATION
    • HETEROCHROMATIN
    • CHROMATIN ASSEMBLY FACTOR-1
    • POLYMERASE I
    • VERTEBRATE CELLS
    • ANTIGENIC VARIATION
    • AFRICAN TRYPANOSOMES

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