A structural and biochemical study is presented concerning the agglutination of gametic flagella, the initial step in the mating reaction of Chlamydomonas reinhardtii. An alteration in the distribution of the intramembranous particles revealed by freeze-fracturing of flagellar membranes is shown to accompany gametic differentiation in both mating types. The isolation and electrophoretic analysis of flagellar membranes and mastigonemes are reported; no electrophoretic differences can be detected when the membrane or mastigoneme glycoproteins from vegetative and gametic cells are compared, nor when glycoproteins from the two mating types are compared, and no novel polypeptides are present in gametic preparations. The membrane vesicles, after they are freed of mastigonemes by sedimentation through a discontinuous sucrose gradient, are extremely active as an isoagglutinin, indicating a direct involvement of the membrane in the mating reaction.As cells differentiate, they are often conferred with unique surface properties that allow extremely selective cellular interactions: the tissue-specific adhesion of dissociated embryonic cells (1), the species-specific reaggregation of dissociated sponge cells (16), and the developmental cycle of agglutinability in Dictyostelium (3) are three prominent examples. Such selective interactions have also been observed in or inferred from studies of simple eukaryotic organisms that undergo mating reactions. Thus, the composition or architecture of the cell surface appears to confer sexual discrimination in Hansenula wingii (7), in Paramecium (29), and in many of the volvocid phytoflagellates which agglutinate through the contact of their flagellar surfaces (31).In this paper we present the results of our observations on the flagellar surface of the phytoflagellate Chlam.vdomonas reinhardtii, which develops the capacity for such specific agglutination reactions after a simple alteration of its growth medium. Specifically, when vegetative C, reinhardtii cells of opposite mating types (rot + and rot-) are induced to differentiate into gametes by nitrogen starvation (19,25) and are mixed together, they agglutinate by their flagellar tips as a prelude to the zygotic cell fusion that occurs several minutes later (described in reference 13). The flagella of vegetative (nongametic) cells exhibit no such agglutinability, nor do certain nonmating mutant strains that have been isolated in this laboratory. Therefore, it should be possible to identify the agglutinins active in this reaction and to study both their mode of action and the 606

No abstract

No abstract

Female Sprague-Dawley rats were fed a control standard diet or a selenite (Se) supplemented diet (1.3 p.p.m. Se) for 8 weeks before mating and during gestation and lactation. Blood glutathione peroxidase activity (GSH-Px) was measured as a biomarker of Se in dames. After mating, the females from two dietary groups were divided into three subgroups (6 groups with 10 animals in each) given 0 (vehicle), 2 or 6 mg/kg methyl mercury (MeHg) by gavage on days 6-9 of gestation. Day 2 post parturition all litters were standardized to 6 pups per litter and remaining pups were used for determination of blood and brain total Hg contents. Behavioural testing was performed at two months of age. The results of the study showed that supplementing the diet with Se partly antagonized some adverse effects of the MeHg such as hypoactivity especially in the high MeHg dose group. There were no changes in physical development or body weight except a tendency to decreased body weight in offspring of mothers exposed to 6 mg Hg/kg. The GSH-Px activity was significantly increased in animals fed on Se supplemented diet. The dietary Se supplementation resulted in considerably increased concentrations of mercury in the blood of the offspring despite milder signs of CNS toxicity and no increase in brain concentrations of mercury.

With the growing concern for the health hazards of occupational exposure to toxic substances attention has been focused on the organic solvents, which are associated with both deleterious nervous system effects and specific tissue injuries. Relatively little is known about the distribution of organic solvents and their metabolites in the living organism. Knowledge of the specific tissue localizations and retention of solvents and solvent metabolites is of great value in revealing and understanding the sites and mechanisms of organic solvent toxicity. Whole-body autoradiography has been modified and applied to distribution studies of benzene, toluene, m-xylene, styrene, methylene chloride, chloroform, carbon tetrachloride, trichloroethylene and carbon disulfide. The high volatility of these substances has led to the development of cryo-techniques. Whole-body autoradiographic techniques applicable to the study of volatile substances are reviewed. The localizations of nonvolatile solvent metabolites and firmly bound metabolites have also been examined. The obtained results are discussed in relation to toxic effects and evaluated by comparison with other techniques used in distribution studies of organic solvents and their metabolites.