"The impact of a globally ageing population cannot be overstated. It is expected that by the year 2025 over a billion individuals will be over 60 years of age. In order to develop strategies aimed to restore and maintain function in ageing individuals, a better understanding of the molecular pathways and biological processes that are involved in ageing and age-related disorders is urgently needed. One of the major mechanisms implicated in the decline of tissue function and ageing is the loss of tissue stem cells. This proposal is aimed at developing a better understanding of two fundamental aspects of stem cell biology: the molecular mechanisms that regulate self-renewal and differentiation and the role of telomere attrition and numerical chromosomal abnormalities in stem cell depletion. For both areas we propose to take advantage of recent improvements in DNA sequencing technology. The first area of interest is the role of sister chromatids in parental (stem) cells on gene expression in daughter cells. For such studies we have developed DNA sequencing techniques that allow identification of specific sister chromatids in single daughter cells using parental DNA template strand sequences. Studies in this area will address an aspect of cell biology that has not been subject to direct experimentation before. For studies on the role of telomere attrition and numerical chromosomal abnormalities in ageing we will use material from humans participating in the LifeLines project in Groningen (160,000 individuals) as well as suitable mouse models. Such studies will employ novel single cell sequencing techniques and telomere length measurements. We are specifically interested to measure telomere dysfunction and aneuploidy in stem cells and more differentiated cells, to identify genetic and other factors regulating human leukocyte telomere length and to study the role of telomere attrition in various leukocytes in relation to normal human ageing and pathology."