Kinetochores, Centromeres and Repetitive DNA

Mechanisms that maintain centromere integrity

Human centromeres are composed of long arrays of repetitive sequences called alpha-satellite DNAs. There are diverse variations of centromere size and organization within and across species, and why and how centromeres maintain this repeat organization remains enigmatic. Recently, we revealed that human centromeric repeats become relatively unstable in cancer cell lines and in primary cells undergoing replicative senescence. By characterizing the key mechanisms that help maintain the repeat sequences, we aim to unveil the functional consequences of centromere instability and their relevance to disease.

Chromosome 1 and 16 have a long heterochromatin region adjacent to the centromere, called juxtacentromeric heterochromatin, which is composed of arrays of satellite 2 and 3 repeats. Activated lymphocytes from Immunodeficiency–Centromeric instability–Facial anomalies (ICF) syndrome cases exhibit hypomethylation and fragility at these juxtacentromeric heterochromatin. We discovered that two proteins, HELLS and CDCA7, whose mutations cause ICF syndrome, form a novel nucleosome remodeling complex that facilitates DNA methylation at the juxtacentromeric heterochromatin.

Key questions:

  • What are the mechanisms that maintain the integrity and copy number of centromere-associated satellite DNAs? Using CO-FISH and quantitative FISH techniques, we have established a method to quantitatively measure those instabilities to address this question.

  • What are the functional consequences resulting from induced instabilities of centromere-associated repetitive sequences?

  • What is the mechanism by which HELLS and CDCA7 promote local DNA methylation at the centromere-associated heterochromatin, and why do their mutations cause centromere instability and immunodeficiency?

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