Role of Chromatin Modifiers in Regulating Human Embryonic Stem Cell Pluripotency
The life of every human starts with a fertilized egg. This single cell starts to divide and, in a truly amazing process, gives rise to a developed human being. Although each cell of a developed organism is a progeny of this single zygote, and shares the same genetic information with every other cell, cells differentiate to specialized forms such as skin, muscle or nervous cells. Thus, new information emerges during development, and is inherited in a fashion that does not involve changes in DNA sequence. This fascinating process is called epigenesis. Epigenetic changes underlie not only normal, but also pathological development. Abnormal epigenesis contributes to human pathology, such as aging, cancer, degenerative diseases, developmental defects and mental retardation.
Embryonic stem cells (ESCs) share with the early embryo the potential to produce every type of cell in the human body. This rare biological property is known as pluripotency. Pluripotency is a unique epigenetic state, in that ESCs can self-renew, while retaining the potential for multilineage differentiation. The research proposed here aims at elucidation of the precise molecular nature of pluripotency.
In the last decade evidence emerged that a substantial portion of epigenetic information is transmitted in a form of chemical modifications of histones and DNA, in particular histone methylation. The physiological template of our genome, called chromatin, is composed of DNA wrapped around histone proteins. Methylation marks are written and erased from histones by specific enzymatic activities and they are read by the specialized proteins to activate or silence gene expression. Here we propose to elucidate which writers, readers and erasers of histone methylation are required for maintenance of the unique epigenetic state of pluripotency. Building on this initial knowledge we will perform a series of biochemical experiments to understand the network of protein-protein and protein-DNA interactions involved in the epigenetic regulation of pluripotency.
We are hoping that our studies will significantly advance our understanding of the unique properties of ESCs and bring us closer to the development of efficient technologies to direct the differentiation of stem cells into therapeutically useful tissues. Even more exciting is possibility that uncovered epigenetic regulators of pluripotency could be used to reset a patient’s differentiated cells to the pluripotent state, thus removing the current bottlenecks in stem cell derivation and requirement for human oocytes, and sidestepping the problems of tissue rejection. Last, but not least, understanding the mechanisms of epigenetic plasticity of human ESCs will contribute to the basic knowledge of human development. Basic knowledge has proven itself time and again to be the raw fabric of innovation and progress in medicine. Thus, in the long run our research may help the humankind in ways we are not yet able to predict.
We believe the proposed research will benefit people of California in the following ways.
It will increase experience and knowledge of human embryonic stem cells among residents of California. This project involves cooperation between two laboratories with complementary expertise. This interaction will facilitate skill exchange and staff training in cutting edge techniques of stem cell biology and epigenetics.
It will result in development of new approaches – the proposed project involves technological approaches that to our knowledge have not been used before in studies of human stem cells, certainly not in the particular combination we propose.
It will generate new reagents to study genetics and epigenetics of human stem cells, which will help position us and other Californian scientists at the forefront of embryonic stem cell research.
We will contribute to basic knowledge of human development. Basic knowledge have proven itself time and again to be a raw fabric of innovation and progress in medicine.
It is highly likely that discoveries resulting from proposed studies will identify molecules whose manipulation will contribute to current efforts to bring stem cell into realm of therapeutics, particularly in the area of directed differentiation and epigenetic reprogramming
We study how chromatin, the complex of DNA and protein that makes up chromosomes, influences expression of genes to produce different tissues and organs in the process of development. Human embryonic stem cells provide a useful model system that allows us to address fundamental questions about role of chromatin modification and epigenetic mechanisms in cell fate decisions governing human development and disease.
With funding from CIRM we developed a human embryonic stem cell-derived in vitro model to study the formation and differentiation of human neural crest, a transient cell population that is ectodermal in origin, but undergoes a major gene expression reprogramming to acquire a remarkably broad differentiation potential and ability to migrate throughout the body to give rise to craniofacial bones and cartilages, peripheral nervous system, and cardiac structures.
We had shown that two distinct chromatin remodelers cooperate to promote the unique epigenetic plasticity and migration of the neural crest cells. Heterozygous mutations in gene encoding one of those remodelers, CHD7, result in a complex constellation of congenital anomalies called CHARGE syndrome, a sporadic, autosomal dominant disorder occurring in about 1:8000 life birth and characterized by malformations of the craniofacial structures, peripheral nervous system, ears, eyes and heart. Though our work we have elucidated for the first time the molecular mechanism underlying this relatively common, but poorly understood human syndrome, and identified novel candidates targets for genes mutated in this disease.