David P. Bazett-Jones

David P. Bazett-Jones

Professor

PhD, University of Toronto, 1981

Address Hospital for Sick Children
Peter Gilgan Centre for Research and Learning
686 Bay St.
Toronto, ON M5G 0A4
Lab Bazett-Jones Lab
Office Phone 416-813-2181
Email dbjones@sickkids.ca

Director
Advanced Bioimaging Centre
Hospital for Sick Children

Canada Research Chair
Molecular and Cellular Imaging

Research Lab

Learn more: Bazett-Jones Lab

Research Description

Ultrastructural Signature of Chromatin Domains within the Nuclei

Our hypothesis is that in mammalian cells the activity of a given gene is a function of its three-dimensional location and organization within its chromosome territory and with respect to other “subnuclear organelles” or sub-compartments in the nucleus. Therefore, the transcriptional program of each cell type should correlate with an ultrastructural signature of chromatin domains within the nuclei of cells of a given cell/tissue type.

Promyelocytic leukemia nuclear bodies (PML NBs or NBs) are a class of subnuclear organelles that contribute to the compartmentalization of nuclear proteins. This process must be important because PML NBs play a central role in cellular differentiation and tumour suppression. Indeed, a number of human cancers are characterized by the down regulation or mutations of PML, including acute promyelocytic leukemia, prostate and colon. Though implicated in processes such as transcription, DNA damage repair, and apoptosis, the exact function of PML NBs is not known.

A prevailing model is that they are storage sites of nuclear proteins, serving as platforms from which they move into the nucleoplasm to carry out their functions. By studying the structure, biochemical composition and dynamics of PML NBs, studies from my laboratory support another model. Though our model does not exclude the storage or platform concepts, we propose that PML NBs interact directly with the surrounding chromatin, and thereby perform a more active role in servicing the regulation of genes on their periphery.

PML Nuclear Bodies

PML (promyelocytic leukemia) protein contributes to the formation of typically 5-30 nuclear bodies per cell, depending on the cell type. These bodies range from approximately 0.2 to 1 micron in diameter. Promyelocytic nuclear bodies (PML NBs) are implicated in a number of cellular processes including transcriptional regulation, apoptosis, DNA repair and replication of both viral and cellular DNA. Our laboratory has provided compelling evidence that PML NBs have an intimate connection to chromatin. The striking detail provided by Electron Spectroscopic Imaging (ESI) of PML NBs reveals that 10 nm chromatin fibres  make physical contacts with the protein-based core of the bodies. Our observation of an increase in the number of PML NBs in early S-phase by fission from pre-existing bodies supports a relationship of the bodies with a set of genomic loci. We are now developing new methods to identify the set of cellular genes that associate with PML NBs

Chromatin Structure

Our lab has studied chromatin at a higher structural level through direct visualization of chromatin fibre organization in mammalian nuclei. We have been able to do this with our pioneering development of ESI, which provides quantitative detection and mapping of nitrogen and phosphorus for distinguishing chromatin from protein-based structures and from RNPs.

We have recently confirmed our hypothesis that the global chromatin configuration is critical in pluripotency. This has been supported by imaging studies of: (1) embryonic stem cell differentiation, (2) chromatin structure changes through early mouse embryogenesis and (3) reprogrammed fully differentiated somatic cells into induced pluripotent stem (iPS) cells. The densely-packed chromatin fibres of constitutive heterochromatin domains (chromocentres) in differentiated mouse embryo fibroblasts (MEFs) become highly dispersed in fully reprogrammed iPS cells. The findings of these studies support our hypothesis that a dispersed state of chromatin fibres defines pluripotency.

  • Transcription regulation
  • Nuclear structure and function
  • Development of molecular and cellular imaging techniques

Publications

View all publications on PubMed

Nano-dissection and sequencing of DNA at single sub-nuclear structures
Chen BK, Anchel D, Gong Z, Cotton R, Li R, Sun Y, Bazett-Jones DP.
Small. 2014 Aug 27;10(16):3267-74  Read

Electron spectroscopic tomography of specific chromatin domains.
Even-Faitelson L, Fussner E, Li R, Strauss M, Bazett-Jones DP.
Methods Mol Biol. 2013;1042:181-95  Read

Open and closed domains in the mouse genome are configured as 10-nm chromatin fibres.
Fussner E, Strauss M, Djuric U, Li R, Ahmed K, Hart M, Ellis J, Bazett-Jones DP.
EMBO Rep. 2012 Nov 6;13(11):992-6.  Read