Wellcome Senior Research Fellow
Patrick Heun is a senior researcher at the Wellcome Centre for Cell Biology, University of Edinburgh. His group is studying the epigenetic inheritance and organisation of centromeres using cultured Drosophila and human cells as a model. This involves the general tools of molecular biology combined with biochemistry and microscopy. Patrick Heun obtained his Ph.D. at the University of Lausanne in the laboratory of Susan Gasser. In 2001, he moved to the Salk Institute, San Diego followed by the Lawrence Berkeley National labs as a postdoctoral fellow with Gary Karpen. In 2005, he started his own lab as a junior group leader at the Max-Planck Institute for Immunobiology and Epigenetics in Freiburg, Germany and moved to the University of Edinburgh as a Wellcome Senior Research Fellow in 2014.
Epigenetic inheritance and organisation of centromeres
Our lab is interested in the epigenetic inheritance and organization of centromeres. Epigenetic transmission of centromere identity through many cell generations is required for proper genome regulation and when perturbed can lead to genome instability and cellular malfunction. We use the fruit fly Drosophila melanogaster and human cells as a model organism to address the following questions:
How is the epigenetic identity of centromeres propagated?
Centromeres are found at the primary constriction of chromosomes in mitosis where they remain connected before cell division. This structure is essential for an equal distribution of chromosomes to the daughter cells.
The centromere specific histone H3-variant CENP-AcenH3 is essential for kinetochore formation and centromere function. We have recently established a biosynthetic approach to target dCENP-AcenH3 to specific non-centromeric sequences such as the Lac Operator and follow the formation of functional neocentromeres. Using this approach we were able to directly demonstrate that a dCENP-AcenH3-LacI fusion is sufficient to induce centromere formation as well as self-propagation and inheritance of the epigenetic centromere mark (Figure 1a and b); Using the LacO/LacI tethering system, we are interested in dissecting the function of centromere factors in Drosophila and human cells for propagation of CENP-AcenH3. This approach has been successfully introduced into a heterologous system comprised of human centromere factors expressed in Drosophila Schneider S2 cells (Logsdon et al., 2015). We are currently trying to reconstitute the loading and self-propagation of either human or Drosophila CENP-A at the ectopic LacO locus (Figure 1c).
What is the role of transcription at the centromere?
Loading of CENP-A at the centromere occurs outside of S-phase and requires the removal of H3 placeholder" nucleosomes. Transcription at centromeres has been linked to the deposition of new CENP-A, although the molecular mechanism is not understood. Interestingly, transcription is able to evict nucleosomes, which can be recycled by the histone chaperone Spt6. We find that centromeric localization of Spt6, RNAPII and centromere-associated transcripts temporally coincides with dCENP-A loading from mitosis to G1. Using fast acting transcriptional inhibitors in combination with a newly developed CENP-A loading system, we demonstrate that centromeric transcription is required for dCENP-A loading by evicting placeholder nucleosomes and promoting dCENP-A transition from chromatin association to nucleosome incorporation. In contrast, loss of parental CENP-A in Spt6 depleted cells underlines the importance of CENP-A maintenance during transcription. Thus, co-operated actions of transcription and Spt6-mediated nucleosome recycling are essential for the stability of the epigenetic centromere mark dCENP-A.
Kyriacou, E. and P. Heun, High-resolution mapping of centromeric protein association using APEX-chromatin fibers.Epigenetics Chromatin, 2018. 11(1): p. 68.
Bobkov, G.O.M., N. Gilbert, and P. Heun, Centromere transcription allows CENP-A to transit from chromatin association to stable incorporation. J Cell Biol, 2018. 217(6): p. 1957-1972.
Anselm, E., et al., Oligomerization of Drosophila Nucleoplasmin-Like Protein is required for its centromere localization.Nucleic Acids Res, 2018. 46(21): p. 11274-11286.
Barrey, E.J. and P. Heun, Artificial Chromosomes and Strategies to Initiate Epigenetic Centromere Establishment. Prog Mol Subcell Biol, 2017. 56: p. 193-212.
Logsdon, G.A., et al., Both tails and the centromere targeting domain of CENP-A are required for centromere establishment. J Cell Biol, 2015. 208(5): p. 521-31.
Padeken, J. and P. Heun, Nucleolus and nuclear periphery: velcro for heterochromatin. Curr Opin Cell Biol, 2014. 28: p. 54-60.
Barth, T.K., et al., Identification of novel Drosophila centromere-associated proteins. Proteomics, 2014. 14(19): p. 2167-78.
Thomae, A.W., et al., A pair of centromeric proteins mediates reproductive isolation in Drosophila species. Dev Cell, 2013.27(4): p. 412-24.
Padeken, J., et al., The nucleoplasmin homolog NLP mediates centromere clustering and anchoring to the nucleolus. Molecular cell, 2013. 50(2): p. 236-49.
Olszak, A.M., et al., Heterochromatin boundaries are hotspots for de novo kinetochore formation. Nature cell biology, 2011.13(7): p. 799-808.
Mendiburo, M.J., et al., Drosophila CENH3 is sufficient for centromere formation. Science, 2011. 334(6056): p. 686-90.