Spatiotemporal regulation of DNA replication in the human genome and its association with genomic instability and disease.

The transmission of genetic information relies on a coordinated network of cell cycle controls. Abnormalities in this network can result in genomic instability and lead to the transformation of normal cells into cancer cells. Chromosomal DNA replication is not only central to cellular division but also plays a crucial role in the maintenance of genomic integrity. DNA replication errors increase genetic instability, and may be a causative factor in diseases such as cancer and neuronal disorders. Replication in eukaryotes initiates from discrete genomic regions, termed origins, according to a strict, often tissue-specific, temporal program. The genetic program that controls activation of replication origins in mammalian cells has still not been elucidated. There is evidence that specification of replication sites and timing of replication are dynamic processes that are regulated by tissue-specific and developmental cues and that are responsive to epigenetic modifications. Here, we focus on the spatiotemporal regulation of DNA replication in the human genome. There is growing evidence that chromosome band patterns and epigenetic transformation of chromatin influence the timing of replication. On the basis of this evidence, we propose that the chromatin regions showing switches in replication timing from early to late in S phase are correlated with chromosome band boundaries. These chromatin regions generally display transitions in GC contents and include more non-B-form DNA structures than other genomic regions. We also examine here the effect of changes in replication timing on genomic stability and the possible role of replication timing in the etiology of diseases such as cancer. Replication timing assays are one of many promising techniques under investigation that may in future allow much earlier cancer detection than is possible today.