[Studies of distribution of phosphorylated H3 in human MCF-7 cells by immunofluroescence labeling]

One of the prominent cell cycle-related modifications of histone proteins whose function is correlated with chromosome condensation is the phosphorylation of histone H3. In this work we used immunofluorescence labeling on human MCF-7 cells with the antibody that was specific for phosphorylated histone H3 at Ser10 to examine the cellular distribution of this protein. The acid-soluble proteins from interphase and mitotic cells were separated by SDS-PAGE and the transferred proteins were probed with the antibody. A strong H3-specific band was only detected in the acid-soluble proteins from mitotic cells, demonstrating the correlation between H3 phosphorylation and mitosis. With confocal microscopy on whole cells, our results showed that mitotic phosphorylation of H3 initiated in discrete foci near the nuclear envelope in early prophase cells. Following initiation, H3 phosphorylation appeared to spread throughout the condensing chromatin and reached maximum in early metaphase cells. Dephosphorylation of H3 began in anaphase cells and was complete immediately prior to detectable chromosome decondensation in telophase cells. There was a precise spatial and temporal correlation between H3 phosphorylation and initial stages of chromatin condensation. The possible functions of the singular phosphorylation of the amino-terminus of H3 were discussed.