Synaptonemal complex aberrations in the pseudoautosomal region of X, Y chromosomes in irradiated hamsters

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.

Meiotic recombination and germ cell aneuploidy

Data on human trisomic conceptuses suggest that the extra chromosome commonly has a maternal origin, and the amount and position of crossing-over on nondisjoined chromosomes is commonly altered. These observations may provide important clues to the etiology of human germ cell aneuploidy, especially in regard to evaluating whether environmental factors play a role. There is concordance of effects of environmental agents on fungi, plants, and animals, which suggests that the overall process of meiosis is well conserved and that chemical and physical agents can affect meiotic recombination, leading to aneuploidy. It seems likely that meiosis in humans will fit the general pattern of meiosis in terms of sensitivity to radiation and chemicals. Thus studies on other organisms provide some insight into the procedures necessary for obtaining useful human data. For example, frequencies of spontaneous meiotic recombination are not uniform per physical length in Drosophila, and different regions of a chromosome respond differently to treatment. Treatments that relieve constraints on the distribution of meiotic exchange, without changing greatly the overall frequency of exchange, may increase the number of univalents and give the impression that there are chromosome-specific responses. Recombination studies that monitor one or a few relatively short genetic regions may also give a false impression of the effects of a treatment on recombination. In addition, meiotic mutants in Saccharomyces and Drosophila highlight a number of processes that are important for production of an exchange event and the utility of that event in the proper segregation of both homologues and sisters. They also suggest that tests for pairing at pachytene, chiasmata at diplotene, and genetic crossing-over may give different results.

Germ line specific factors in chemical mutagenesis

Chemical mutagenesis test results have not revealed evidence of germ line specific mutagens. However, conventional assays have indicated that there are male-female differences in mutagenic response, as well as quantitative/qualitative differences in induced mutations which depend upon the particular cell stage exposed. Many factors inherent in the germ line can be speculated to influence chemical transport to, and interaction with, target cell populations to result in mutagenic outcomes. The level of uncertainty regarding the general operation of such factors, in combination with the limited availability of chemical test data designed to address comparative somatic and germ cell mutagenesis, leaves open the question of whether there are mutagens specifically affecting germ cells. This argues for a conservative approach to interpreting germ cell risk from somatic cell mutation analysis.