Abstract
Accurate replication of DNA once and only once per cell cycle is an essential process for all living organisms. Despite many studies aimed at understanding this phenomenon, no mechanism describing where and when replication initiates in mammalian cells has yet been elucidated. However, it is well established that DNA is replicated as megabase-sized chromosomal segments called domains in a specific temporal order during S phase. The order in which these segments replicate is called the replication timing program. In recent years, approaches using microarray technology have been developed to study replication timing throughout the entire genome (Hiratani et al., 2008; Hiratani et al., 2010; Woodfine et al., 2004). These approaches have allowed the study of genome-wide replication timing patterns throughout various stages of mouse embryonic stem cell development, and led to the discovery that replication timing is a cell-type specific, developmentally regulated event with epigenetic significance (Hiratani et al., 2010; Ryba et al., 2010). Here I use the genome-wide replication timing assay to study replication timing patterns in human cell types. Specifically, I have investigated whether significant differences in replication timing exist in human embryonic stem cell lines cultured under various growth conditions. In collaboration with other stem cell biologists I have performed genome wide replication timing analysis on primed and naïve human pluripotent cell types. Finally, in a separate but related project, I have used the genome wide replication timing assay to compare replication timing in normal B lymphoblasts to replication timing in established leukemic cell lines and leukemia patient samples in order to probe for the existence of leukemia specific changes in replication timing that may be linked to known genetic subtypes of leukemia or prognoses.
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