Biography: Dr Lee Wong
After completing a Bachelor of Science Degree at Monash University I undertook an Honours year in the Interferon Laboratory, Department of Biochemistry and Molecular Biology under the supervision of Dr Stephen Ralph. I continued on with the same project into my Ph.D. The focus of my PhD study involved the investigation of the components in interferon signaling pathway and the elucidation of the mechanism underlying the resistance of melanoma to interferon treatment. After my PhD, I worked as a postdoctoral fellow with Prof Andy Choo at Murdoch Childrens Research Institute to study chromosome biology. I have recently established a new research group at the Department of Biochemistry and Molecular Biology. Our aim is to establish ourselves as internationally competitive researchers in the fields of chromosome and epigenetic research in stem cells and cancers. Our research objectives are: 1) to understand the mechanism underlying the establishment and regulation of centromere and telomere chromatin in stem cells and cancers; 2) to understand epigenetic reprogramming during stem cell differentiation and early embryo development.
1) To define the epigenetic determinants of human neocentromeres and centromeres
Neocentromeres are centromeres that form at the normally gene-encoding regions of chromosomes and are devoid of centromeric α-satellite DNA. The best-studied neocentromere to date is 10q25 neocentromere on a chromosome 10 variant, mardel(10). The formation of neocentromeres in genomic regions with no apparent overall sequence homology strongly implicates the involvement of complex epigenetic players in centromere identity and function. Neocentromeres provide an ideal system for molecular analysis of centromere chromatin. With my colleagues, we have been the first to show the DNA methylation and transcription profiles across a human centromere. We have also provided evidence that single-stranded non-coding RNA is a key component for the assembly of a nucleoprotein complex at the centromere and neocentromere, suggesting the existence of a novel mechanism based on the participation of centromeric RNA in the assembly and proper functioning of the centromere. In a recent study, we have identified a unique role of RNA polymerase II in driving centromeric transcription during mitosis and this transcriptional activity is essential to ensure proper chromosomal segregation.
For the future plan, I will extend this work to stem cell research to elucidate how centromere chromatin is regulated in pluripotent cell types and cancers. This is important because centromere chromatin undergoes significant changes during stem cell differentiation and cancer formation. The knowledge gained should (1) increase our insight into the organisational and regulatory properties of the human centromere; (2) translate into our understanding of the aetiology of clinical problems caused by an imbalance in chromosome number, eg. in aneuploidy, and cancer development.
2) To study the epigenetic regulation of telomere chromatin in embryonic stem cells and cancers
i) The capacity for continual telomere length renewal is important to the maintenance of pluripotency in embryonic stem (ES) cells, but neither the detailed telomeric chromatin structure nor the mechanism for regulating the continual telomere length renewal have been defined. Telomeres are enriched with histone modifications characteristic of silenced chromatin. However, I have shown that ES cell telomeres are enriched with H3.3, a histone H3 variant associated with active and open chromatin. Upon differentiation, H3.3 level at the telomere decreases, accompanied by increased levels of repressive histone marks. My study is first to show the existence of a unique telomere chromatin that undergoes dynamic differentiation-dependent remodelling in ES cells. I will study the role of H3.3 as a key epigenetic reprogramming determinant in adult progenitor/stem cells eg. stromal, mesenchymal and neural stem cells.
ATRX (alpha-thalassemia mental retardation) is a member of SNF2 family of helicase/ATPases. I have shown evidence that ATRX involves in the assembly of H3.3 nucleosomes at ES cell telomeres, implicating a novel function of ATRX in regulating ES cell pluripotency. In future studies, I will examine the effect of ATRX RNAi-knockdown and knockout in mouse ES cells on telomere structure and function ie. changes in telomere length and structural integrity chromatin modifications. I will also determine if the roles of H3.3 and ATRX extends in adult progenitor/stem cells, mouse early embryos and mouse germ cells.
In ES cell system, I will define a novel pathway involved in the regulation of telomere length homeostasis and structural organization. My study will provide critical insight into our current understanding of self-renewal and maintenance of pluripotency in ES and other stem cells, early embryogenesis, ageing process, and cancer development.
ii) Human ALT (Alternate Telomere Maintenance) cancer cells are cells that have telomere length of >50 kb. These cells do not contain any telomerases and maintain telomere length by a DNA recombination based mechanism. ALT mechanism is used in 15% of human cancers eg. sarcomes. A recent study reports a common mutation of ATRX and its interacting partner in ALT cancers. Given the importance of ATRX in regulation of H3.3 deposition, I will determine if mutation of ATRX affects establishment of epigenetic marks at telomeres and in the global chromatin in ALT cancer cells. The loss of a proper inheritance of epigenetic marks at telomeres in ALT cancers may drive indefinite telomere elongation, hence promoting an unlimited cellular lifespan in these cancers.
The existence of ALT for telomere maintenance in cancers raises the possibility that telomerase-positive tumours undergoing anti-telomerase therapies might escape by activating the ALT pathway. For these reasons, it is important to delineate the ALT mechanism to have a clearer picture of the tumorigenic process and the development of specific chemotherapeutic intervention targeting ALT-specific cancers. Our work will unveil a novel telomere maintenance mechanism that is central to the proliferation of ALT cancers. It will have an impact on our understanding of the behaviour of ALT cancers in terms of the underlying mechanism for telomeric alterations accompanying malignant transformation and potential target for the clinical treatment of these cancers.
The Research Team
Postdoctoral fellow: Dr Lyn Chan
Research assistant: James McGhie
PhD students: Fiona Chang and Julie Chan