Morphology of nuclear ribonucleoproteins in the early period of liver regeneration after irradiation

Radiation response of cell organelles

The cellular responses to various form of radiation, including ionizing- and UV-irradiation or exposure to electromagnetic fields is manifested as irreversible and reversible structural and functional changes to cells and cell organelles. Moreover, beside the morphological signs related to cell death, there are several reversible alterations in the structure of different cell organelles. The radiation-induced changes in the supramolecular organization of the membranes, including plasma membrane, and different cell organelle membranes, play a significant role in the development of acute radiation injury. These signs of radiation-induced reversible perturbation biological membranes reflect changes in the organization and/or composition of the glycocalix, modified activity and/or distribution of different membrane domains, including enzymes and binding sites. The observed changes of the cell surface micromorphology and the alteration of intercellular connections are closely related to the reorganization of the cytoskeletal elements in the irradiated cells. The mitochondria, endoplasmic reticulum, Golgi-complex, the lysosomal system have long been considered to be direct intracellular targets of irradiation. The listed morphological alterations of nuclear chromatin (e.g. changes of fine structure, altered number of nucleolar organizing regions and micronuclei, development of chromosome aberrations) may originate from the radiation-induced damage to the supramolecular organization of DNA and/or nucleus specific proteins. These endpoints of radiation effects resulted as direct consequence(s) of absorbed radiation energy, and indirectly altered intra-, intercellular communication or modified signal transduction. Some complementary data suggest that all these effects are not strictly specific to radiation and may be best considered as general stress responses, similar to those observed after application of various injurious agents and treatments to cells. Moreover, they may be equally responsible for direct degradation of supramolecular component of cells, altered signal transduction, or changes in the amount or ratio of any extracellular mediators upon irradiation. Nevertheless, qualitative and/or quantitative evaluation of any changes of chromosomes by different techniques (morphological analysis of metaphase chromosomes, fluorescent in situ hybridization, development of micronuclei etc.) are useful biological indicators as well as "biological dosimeters" of radiation injury. It is suggested, that some modern methods such as immunohistochemical detection of different proteins, specific markers of cell organelles and cytoskeleton, inspection of distribution of cell surface charged sites and different membrane domains and application of tracer substances may all be included into protocols for evaluation of cell alterations induced by different types and intensities of radiation.

Increase in nucleoli after x-radiation of fibroblasts of patients with Gorlin syndrome

Gorlin syndrome (GS) is an autosomal dominant disorder in which patients are abnormally susceptible to ionizing radiation with radiotherapeutic doses. Radiogenic basal cell carcinomas may develop with a short latent period in patients. The mechanisms underlying the abnormal radiosusceptibility of cells in patients with GS has not been well characterized. In this study we report an increase in the number of nucleoli in fibroblast cells from 3 patients with GS after x-radiation. In GS fibroblasts, the increase in nucleolus number concomitant with the increase of ribonucleoprotein immunoreactive aggregates within the nucleus was observed after x-radiation, whereas significant change was not found in normal fibroblasts derived from healthy donors. This increase disappeared when cells were cultured with the RNA synthesis inhibitor actinomycin D after x-radiation but not when they were cultured with cycloheximide or aphydicolin, which are protein and DNA synthesis inhibitors, respectively. Ultraviolet exposure did not induce remarkable changes in the GS nucleoli. Thus the increase in nucleoli was induced after x-radiation of GS fibroblasts, and this increase seemed to be related to RNA synthesis metabolism.