Chromosomes are found in all organisms that have a cell nucleus, and carry the organism’s hereditary material. During cell division, chromosomes divide and distribute equally to the daughter cells. Errors in the division process can result in daughter cells that contain an incorrect number of chromosomes. Known as aneuploidy, this state is responsible for many genetic diseases and is characterized by a specific type of genome instability known as Chromosome Instability (CIN). Because chromosome stability is a fundamental requirement across all organisms, it can be studied using simpler organisms, such as baker’s yeast. Genome wide screens on yeast have identified approximately 300 genes important for maintaining chromosome stability (CIN genes). A subset of these genes has also been found to be mutated at an elevated rate in some human cancers, which suggests that these genes contribute to tumour progression and development. Mutations in these key genome stability genes may also represent an Achilles’ heel for tumours. Enhancing chromosome instability to a point where tumour cells can no longer function and reproduce could halt their division or lead to cell death. Jessica McLellan is studying the subset of CIN genes mutated in colon cancer. She specifically aims to identify genes that, when mutated in combination with a CIN gene mutation, lead to cell death. By exploiting the mutations seen in many types of cancers, this project could lead to the development of novel cancer therapeutics that are less harmful to non-cancer cells than current treatments. McLellan’s research will increase our understanding of the complex biological processes that ensure genome stability and the mechanisms by which these processes can become deregulated.
Research Pillar: Biomedical
The Role of beta-catenin Stabilization in the Synaptic Pathology of Alzheimer’s Disease
Alzheimer’s disease (AD) is a devastating neurological disorder characterized by the loss of cognitive function and an inability to process and store new memories, caused by the progressive death of neurons (brain cells). It is becoming increasingly evident that before neurons die, changes can be observed at their synapses – the junction between neurons across which information is transmitted. Deficits in synaptic function, loss of synapses, and a reduced ability to form new synapses are the major correlates of dementia. It is therefore crucial to understand the basic biology of synapses, and how these processes are affected in AD. The cadherin family of cell adhesion molecules and their intracellular partner, b-catenin, play a critical role in regulating the formation and remodelling of synapses. Both molecules also associate with presenilin-1 (PS1), a protein that normally degrades (breaks down) b-catenin. Mutations in the PS1 gene account for nearly 70 per cent of early-onset familial AD cases. Fergil Mills is investigating the effects on neurons when b-catenin is not normally degraded by PS1. Using isolated neurons and a mouse model, he is characterizing the synaptic consequences of stabilizing (maintaining) b-catenin in neurons, and determining the molecular mechanisms of b-catenin in the development of synaptic structures. These studies will help determine whether b-catenin stabilization leads to the synaptic pathology and cognitive deficits seen in AD. Mills’ studies will further our understanding of synapse pathology and cognitive deficits, and could lead to new treatments for patients with AD or other neurological disorders.
The role of SHIP's C2 and PH domains in regulating hematopoietic cell growth and function
Various cancers and inflammatory diseases occur as a result of inappropriate activation of the body’s blood-forming hematopoietic cells. Normally, cellular activation, growth and survival in hematopoietic cells are regulated by the phosphoinositide 3-kinase (PI3K) pathway, which drives a wide range of cellular processes. Keeping tight control on this pathway is SHIP (SH2 domain-containing inositol 5′ phosphatase), a counteracting enzyme that inhibits PI3K action. SHIP is found only in blood and immune system cells and is the major restraining mechanism in these cell types. Loss or impaired activity of SHIP – in effect, removing the brakes on the PI3K pathway – has been implicated in certain leukemias and in inflammatory disease. Recently, researchers discovered small molecules that are capable of enhancing SHIP activity, resulting in both the inhibition of immune cell activation and the death of hematopoietic cancer cells. This represents a previously unknown mode of regulating SHIP enzyme activity. Andrew Ming-Lum is determining the significance of this novel type of regulation of SHIP function. Using cell lines and mouse models, he is focusing on a previously unrecognized domain on the enzyme, upon which the small molecules are believed to act. These studies will provide greater insight into how this mechanism affects the function, growth and survival of hematopoietic cells. It will also provide insight into the dysregulation that occurs in certain cancers and inflammatory diseases.
Unraveling transcriptional regulatory networks governing mouse development
The genome of each cell within an organism contains hereditary information. Among other features, the genome contains genes – DNA sequences that specify the genetic code (encode) for functional products such as proteins. The product of a gene is produced when the gene is turned on (expressed). The process of turning certain genes on or off is governed by regulatory proteins called transcription factors (TFs). While cells of different tissues within an organism contain the same genome, their function may be different due to the fact that they express different genes. While in simpler organisms gene expression is regulated by individual TFs, in more complex organisms such as mammals, several TFs may work together to control the expression of a gene. Many complex diseases such as cancer are at least partially due to improper expression of certain genes. Understanding how gene expression is regulated in an organism, including identifying what TFs work together to regulate particular genes, is instrumental to understanding the biology of numerous health conditions. Olena Morozova is working as part of a large research project aimed at identifying genetic networks governing development. Using the mouse as a model system to study the regulation of gene expression, she is focusing on how different TFs interact to regulate the development of mouse pancreas, heart, and liver, and how these interactions can be used to identify master regulators and the main control nodes in the development of these organs. Overall, this project will provide invaluable insights into mammalian gene regulation and will ultimately help to understand the biology of diseases resulting from errors in the regulation of gene expression. The identified TFs that work together with many other TFs are potentially useful targets for effective disease therapy.
Escape from mitotic arrest; compounds that induce mitotic slippage as tools for chemical biology and potential therapeutic agents
One of the main characteristics of cancer is the uncontrolled division and growth of cells. Because tumour cells divide very frequently, tumour growth can be selectively stopped by inhibiting cell division. Commonly-used cancer drugs act by effectively “freezing” cell activity right in the process of division. This is done by interfering with mitosis – the point in the cell cycle where the nuclear chromosomes have been duplicated and separated to form two daughter cells. Unlike normal cells, some cancer cells eventually bypass this frozen state in a process known as mitotic slippage. However, the resulting cells now contain too many sets of chromosomes. Researchers still don’t know what happens to these drug-treated cancer cells as a result of mitotic slippage – whether they are able to start dividing again, whether they remain in an arrested state indefinitely, or whether they die. Jenna Riffell is investigating the fate of cancer cells after drug treatment. She is identifying chemical compounds that can stimulate drug-treated cancer cells to undergo mitotic slippage, and monitoring what happens to these cells. Her hypothesis is that the rate of mitotic slippage can be increased with chemicals, and will prompt growth arrest or cell death. If proven successful, this approach could be used for the development of future cancer therapies. In addition, Riffell’s work will be useful for studying the underlying biochemical mechanisms of cell division.
RNA interference analysis of human embryonic stem cells in a microfluidic device
Embryonic stem cells (ESCs) are considered the pinnacle stem cell due to their unlimited capacity to self-renew. Since ESCs can differentiate to produce precursors to almost all types of cells (pluripotency), they may hold the key to curing diseases that are caused by the loss of function among specific cell types such as Parkinson’s disease, Alzheimer’s disease, spinal cord injuries, and type 1 diabetes. In order to understand differentiation and self-renewal, researchers compare gene activity between ESCs that have undergone differentiation and those that have not. Scientists can also intentionally turn off (silence) specific genes to see if there is an effect on cell pluripotency. Conventional techniques are time consuming and only allow for the analysis of large numbers of cells at any given time. The cells in these populations are rarely homogeneous as the environments around them are not precisely controlled. To address these issues, researchers have developed a cutting edge technology called microfluidics. Microfluidic technology involves constructing small chips with thousands of fluid-filled chambers that can each contain a single cell. This reduces the number of cells used and the cost of each experiment, and allows thousands of experiments to be performed on a single chip simultaneously. Darek Sikorski is constructing a microfluidic device for the purpose of sustaining and examining the behaviour of ESCs. Once validated, this will allow for large-scale experiments to be performed where specific genes are silenced in each cell, allowing for the analysis of thousands of genes at once. This technology has the potential to greatly accelerate research into how ESCs grow, communicate and differentiate. Ultimately, this could lead to ways to use ESC lines to produce specialized tissues that can cure certain diseases.
YB-1 is associated with breast cancer relapse because it induces tumour-initiating cells
In 2007, an estimated 22,300 Canadian women were diagnosed with breast cancer, and 5,300 women died of the disease. To kill cancer cells, breast cancer patients undergo combinations of surgery, drug therapies, chemotherapy, and radiation. In spite of these aggressive treatments, certain cancer cells may not be completely eradicated and tumours may start growing again (relapse). In the event of breast cancer relapse, the prognosis is generally much worse than it was at the initial onset of the disease, and available drugs eventually become ineffective. It has been discovered that in breast cancer, only a small group of cells – called breast cancer tumour-initiating cells – can keep growing for a long period of time, while the other “”regular”” cancer cells cannot sustain themselves long term. With a better understanding of these aggressive tumour-initiating cells, researchers could design new drugs that target this special group of cells, and focus less on the cancer cells that will eventually stop growing on their own. Preliminary evidence suggests that tumour-initiating cells require a protein called YB-1 in order to grow and form tumours. Studies also show that patients whose breast cancers produce YB-1 have a higher chance of relapsing. Karen To is investigating whether she can stop the growth of tumour-initiating cells by blocking the production of YB-1. If this particular factor is proven essential for the growth of the tumour-initiating cells, drugs could then be designed to remove this protein. To’s research will contribute to the understanding of the small group of breast cancer cells responsible for maintaining tumour growth. Ultimately, this knowledge could lead to improved ways to treat this devastating disease.
Cross-species characterization of proteins involved in genomic stability
Cell division is required for the development, growth, renewal and repair of all organisms, including humans. During cell division, the cell’s genomic information – stored in the chromosomes – is replicated (copied) so that each of the resulting daughter cells receives a complete set of genetic material. Proper segregation of chromosomes to daughter cells during cell division is critical to their continued survival, and chromosome missegregation has been observed in a majority of cancers. However, the connection between the increased rate of chromosome missegregation observed in cancer, and the development of the cancer itself, remains unclear. Because chromosome segregation is a fundamental mechanism in all organisms, baker’s yeast can be used as a model to study this process. Many yeast genes and proteins involved in chromosome segregation appear to be conserved across evolution between yeast and humans. One such protein in yeast is Ctf4, which has a human counterpart called Wdhd1. Ctf4 plays a critical role in ensuring faithful chromosome segregation during cell division, though its biochemical function is not fully understood. The yeast CTF4 gene also appears to interact genetically with a number of yeast genes whose human counterparts are known to be mutated in cancer. Derek van Pel is further characterizing both the human and yeast proteins’ roles in this chromosome segregation. He is using biochemical techniques to isolate any other proteins within the cell with which these proteins interact. Such interactions will then offer clues to the function of these proteins. Derek’s research will shed light on the role of Ctf4/Wdhd1 in ensuring proper chromosome segregation, and possibly the role of this process in cancer development. Understanding these genetic interactions may also lead directly to new therapeutic avenues for cancer.
Microfluidic instrumentation for microRNA expression profiling in hematopoietic stem cells
MicroRNAs (miRNAs) are small RNA molecules that regulate the expression (activation) of genes. Recent studies of miRNA expression implicate these molecules in early development, brain development, cell proliferation and cell death. They are also implicated in disease states, such as chronic lymphocytic leukemia. Determining how, when, and where miRNAs are produced and function in cells and tissues would have profound impact on medical disciplines ranging from embryology to cancer diagnosis and therapy. The genes expressed in miRNA differ between developing and mature tissues, and comparing normal tissues to tumour tissues also reveals different miRNA expression profiles. Further studies looking at differentially expressed miRNAs could help identify those miRNAs involved in human cancer development. Unfortunately, traditional expression profiling techniques are laborious, costly, slow, or lack the sensitivity to effectively screen populations of cells and quantify miRNA content. A promising approach to overcome these limitations is the use of microfluidics technology. This technology involves constructing small chips with thousands of fluid-filled chambers, which can each contain a single cell. This reduces the number of cells used and the cost of each experiment, and allows thousands of experiments to be performed on a single chip simultaneously. Adam White is developing a microfluidic device capable of inexpensive miRNA expression profiling of many single cells at the same time. Upon successful development of this new microfluidic tool, he will work with other scientists to look for differentially expressed miRNAs in blood related cancers such as acute myeloid leukemia. The development of a microfluidic device for single cell analysis of miRNA would greatly accelerate the identification of those miRNAs involved in cancer development, and ultimately improve methods of cancer diagnosis and treatment.
Improved characterization of orthologs to facilitate cross-species analysis of innate immune system gene responses
The innate immune system is the body’s first line of defense to protect us from disease-causing microbes in our environment. However, the innate immune system can also generate other unintended and serious effects such as prolonged – and sometimes fatal – inflammation. The study of human systems such as the innate immune system is assisted by examining similar systems in other organisms, known as model organisms. Researchers link equivalent genes in the model organism to human genes, so that knowledge can be transferred from the model organism to humans. However, identifying equivalent genes between species can be a difficult task. The Brinkman laboratory at Simon Fraser University has developed a software program called Ortholuge that can detect pairs of genes that are likely to be “orthologs” – genes in different species that are similar to each other because they originated from a common ancestor. Orthologs are of significant interest when inferring function in humans based on different species, or when linking equivalent genes between species for large scale comparative analyses. Matthew Whiteside is working to improve the accuracy and speed of Ortholuge, adding functionality to the program that will resolve some of the more complex gene relationships. He will then use the software to perform a large-scale study of the innate immune system in humans, mice and animals important in agriculture, such as cattle. Whiteside’s work will be the first large-scale cross-species comparative analysis of the innate immune system. He hopes that this study will provide fundamental new insights regarding the evolution of innate immune system. This analysis may also highlight important innate immunity genes that are conserved between the species, with potential for identifying new therapeutic targets for immune diseases.