Nuclear Translocation of a Pre-mRNA Splicing Factor, p100prp1/zer1/prp6, in Mouse 1-cell Embryos

Zygotic gene activation (ZGA) is initiated at the late 1-cell stage in the mouse. At this time a number of nuclear proteins involved in transcription regulation, RNA synthesis as well as RNA processing are translocated from the cytoplasm to the nuclei of the zygotes. In the present series of experiments, we demonstrated the developmentally regulated subcellular localization of p100prp1/zer1/ prp6 (also called U5-102 kDa protein), which was previously identified by us as a human homologue of Prp1p/Zer1p of Schizosaccharomyces pombe and Prp6p of Saccharomyces cerevisiae, and found to be tightly associated with the U5 small nuclear ribonucleoprotein particle. Both Prp1p/Zer1p and Prp6p are important regulators of pre-mRNA processing and cell cycle progression in yeast. Immunocytochemical analysis revealed that p100prp1/zer1/prp6 was gradually translocated into the pronuclei from the cytoplasm in mouse 1-cell embryos. The nuclear translocation of p100prp1/zer1/prp6 was not prevented by treatment of 1-cell embryos with aphidicolin, indicating that the translocation is independent of DNA synthesis. These findings suggest that p100prp1/zer1/prp6 is involved in pre-mRNA processing during preimplantation development, including the onset of ZGA in the mouse embryo.