Translocation of Histone H1 Subtypes Between Chromatin and Cytoplasm During Mitosis in Normal Human Fibroblasts

• Histone H1 is an important constituent of chromatin which undergoes major structural rearrangements during mitosis. However, the role of H1, multiple H1 subtypes and H1 phosphorylation is still unclear. In normal human fibroblasts, phosphorylated H1 was found located in nuclei during prophase and in both cytoplasm and condensed chromosomes during metaphase, anaphase and telophase as detected by immunocytochemistry. Moreover, we detected remarkable differences in the distribution of the histone H1 subtypes H1.2, H1.3 and H1.5 during mitosis. H1.2 was found in chromatin during prophase, and almost solely in the cytoplasm of metaphase and early anaphase cells. In late anaphase it appeared in both chromatin and cytoplasm, and again in chromatin during telophase. H1.5 distribution pattern resembled that of H1.2, but some H1.5 remained situated in chromatin during metaphase and early anaphase. H1.3 was detected in chromatin in all cell cycle phases. We propose therefore, that H1 subtype translocation during mitosis is controlled by phosphorylation, in combination with H1 subtype inherent affinity. We conclude that H1 subtypes, or their phosphorylated variants, may be signalling molecules in mitosis or that they leave chromatin in a regulated way to give access for chromatin condensing factors or transcriptional regulators during mitosis.

Nyckelord

Histone H1

Chromatin

Cell cycle

Mitosis

MEDICINE

MEDICIN

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