Dynamic Organization of DNA Replication in One-Cell Mouse Embryos: Relationship to Transcriptional Activation

Abstract

We have analyzed the spatial and temporal relationship between transcription and replication sites during the first cell cycle in mouse embryos. Embryos were microinjected with both 5-bromouridine-5'-triphosphate and digoxygenin-11-deoxyuridine-5'-triphosphate to visualize transcription and replication sites respectively. We detected six different phases of replication during S phase and dated the onset of zygotic transcription at the end of the S phase. Using confocal microscopy, we showed that there is essentially no colocalization of replication and transcription sites at this stage of development. Moreover, studies on aphidicolin-treated embryos demonstrated that inhibition of DNA replication does not hinder transcriptional activation at the 1-cell stage.