The relationship between DNA replication and human genome organization.
Résumé
Assessment of the impact of DNA replication on genome architecture in Eukaryotes has long been hampered by the scarcity of experimental data. Recent work, relying on computational predictions of origins of replication, suggested that replication might be a major determinant of gene organization in human (Huvet et al., 2007). Here, we address this question by analyzing the first large-scale dataset of experimentally determined origins of replication in human: 283 origins identified in HeLa cells, in 1% of the genome covered by ENCODE regions (Cadoret et al., 2008). We show that origins of replication are not randomly distributed, as they display significant overlap with promoter regions and CpG islands. The hypothesis of a selective pressure to avoid frontal collisions between replication and transcription polymerases is not supported by experimental data, as we find no evidence for gene orientation bias in the proximity of origins of replication. The lack of a significant orientation bias remains manifest even when considering only genes expressed at a high rate, or in a wide number of tissues, and is not affected by the regional replication timing. Gene expression breadth does not appear to be correlated with the distance from the origins of replication. We conclude that the impact of DNA replication on human genome organization is considerably weaker than previously proposed.