Dynamic distribution of Thr3-phosphorylated histone H3 in CHO cells in mitosis

The phosphorylation of histone H3 at Ser10, Ser28, Thr11 and Thr3 of the amino terminal has been proved related to mitosis of the mammalian cells. However, the function of the Thr3 phosphorylation of H3 remains unclear. In this study, indirect immunofluorescence labelling and laser confocal microscopy were used to examine the cellular dynamic distribution of Thr3-phosphorylated H3 at mitosis in CHO cells. The results showed that the Thr3 phosphorylation began at early prophase and spread throughout the chromosomes at late prophase. At metaphase, most of the Thr3-phosphorylated H3 was distributed along the entire chromosomal arms and maintained until early anaphase. During late anaphase and telophase, the fluorescent signal of Thr3-phosphorylated H3 disappeared from chromosomes. There was a precise spatial and temporal correlation between H3 phosphorylation of Thr3 and stages of chromatin condensation. The timing of Thr3 phosphorylation and dephosphorylation in mitosis were similar to that reported for Thr11 phosphorylation of H3. The Thr3-phosphorylated H3 localized along the arms of chromosomes during metaphase and early anaphase. It was different from the Ser10-phosphorylated H3, which localized at telomere regions, and Thr11-phosphorylated H3, which localized at centromeres. The results suggest that the Thr3 phosphorylation of histone H3 may play a specific role, which is different from Ser10 phosphorylation and Thr11 phosphorylation in mitosis.