Factors influencing the Staining of Histones in Irradiated Rat Thymocytes

Abstract

THE most striking cytological event which accompanies the death of thymic lymphocytes is the complete loss of nuclear structure (pycnosis), as seen in fixed and stained preparations or in unstained cells with phase contrast optics^1–3. Irradiation strongly accelerates this phenomenon and structurally homogeneous nuclei begin to accumulate in thymocyte cultures between 0.5 and 1.0 h after irradiation with doses between 500 and 1,500 r. According to Whitfield et al.^1,2, the loss of nuclear structure is accompanied by marked changes in the localization and extractability of histones with hot trichloroacetic acid (TCA). The histones, which are normally localized in the condensed chromatin aggregates of the healthy interphase nucleus, come to be evenly distributed throughout the damaged nucleus while some escape into the cytoplasm. The histones which do remain in the nucleus become abnormally extractable with hot TCA.