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 con focal microspectrofluorimeter was used to measure the internal pH (pH(i)) i n different subcellular and subnuclear compartments of early mouse embryos. By this method we analysed the first cell cycle of naturally fertilised em bryos in order to detect possible pH(i) changes correlated to cellular even ts, particularly the onset of replication or transcription and the first mi tosis. Throughout interphase, significant differences of pH(i) were observe d between cytoplasm and pronuclei, and, even more striking, between these c ompartments and nucleolus precursor bodies, whose pH(i) was systematically lower. We could detect significant pH(i) change neither during the replicat ion 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 p rocess that seemed specifically correlated with mitosis. (C) 2000 Editions scientifiques et medicales Elsevier SAS.