Intracellular pH in one-cell mouse embryo differs between subcellular compartments and between interphase and mitosis

The pH-sensitive dual-emission fluorophore SNARF-1 coupled with a laser confocal microspectrofluorimeter was used to measure the internal pH (pH(i)) in different subcellular and subnuclear compartments of early mouse embryos. By this method we analysed the first cell cycle of naturally fertilised embryos in order to detect possible pH(i) changes correlated to cellular events, particularly the onset of replication or transcription and the first mitosis. Throughout interphase, significant differences of pH(i) were observed between cytoplasm and pronuclei, and, even more striking, between these compartments and nucleolus precursor bodies, whose pH(i) was systematically lower. We could detect significant pH(i) change neither during the replication phase nor at the onset of zygotic transcription, but pH(i) increased at the end of the one-cell stage in both cytoplasm and chromatin regions, a process that seemed specifically correlated with mitosis. (C) 2000 Editions scientifiques et medicales Elsevier SAS.