In vitro assessment of the toxicity of metal compounds

A review has been compiled illustrating the directions taken in examining the genotoxic effects of metals and their compounds centering only on those studies pertaining to effects of metals and their compounds on DNA structure and function, such as the induction of DNA strand breaks, production of DNA-protein crosslinks, induction of chromosomal aberrations, and sister chromatid exchanges. Although it is premature to declare a cause and effect relationship between the carcinogenic activity of metals and their ability to induce one or more lesions in DNA, strong evidence is emerging to suggest such a relationship. Low concentrations of metals induce the appearance of DNA lesions, such as strand breaks and crosslinks, or induce sister chromatid exchanges or DNA repair synthesis. Assays based upon these events constitute extremely sensitive probes for genotoxic effects of metals and their compounds. These effects of metals on DNA are consistent with the currently accepted mechanism of chemical carcinogenesis, allowing the acquisition and propagation of altered DNA function. The lack of complete information on the activity of metals in producing DNA lesions allow only preliminary conclusions to be drawn. Certain compounds containing potentially or actually carcinogenic elements, such as Ni, Be, As, Cr, Cd, and to a minor extent Pb, have yielded positive responses in one or more DNA lesion assays. At relatively nontoxic levels of Ni and Cr, considerable evidence suggests that multiple types of DNA lesions are induced.     

Use of 6-diazo-5-oxo-l-norleucine to study interaction between myocardial glycoconjugate secretion and endothelial activation in the early embryonic chick heart

The glutamine analog, 6-diazo-5-oxo-l-norleucine (DON), a glycoconjugate inhibitor, was used to probe the relationships between myocardial secretion of extracellular matrix and endothelial differentiation and formation of cushion mesenchyme (primordia of AV values). When DON was given to stage 12 chick embryos maintained in shell-less culture, the myocardial secretion gradient of glucose- and sulfate-labeled matrix was blocked. Concomitantly, the endothelium failed to complete activation but continued to divide and incorporate thymidine. By varying DON concentration, two distinct phases of endothelial differentiation were identified: the first (labile to 0.5 μg) involved hypertrophy, the second (labile to 0.25 μg) acquisition of migratory appendages with resultant mesenchyme formation. Glucosamine + DON (but not inosine, glucose, or glutamine) restored the matrical secretion gradient and to varying degrees both phases of endothelial activation. Endothelia totally suppressed from forming mesenchyme in situ acquired this capacity when explanted into three-dimensional collagen gel culture. The capacity was enhanced by glucosamine given in situ as an inhibitory override, dependent upon serum concentration, inhibited by heat-inactivated serum or by adding DON to the medium, but unaffected by hyaluronate. These results were compared to those obtained by co-culturing endothelium and myocardium and discussed in terms of the hypothesis that cushion mesenchyme formation results from an epithelial interaction mediated by glycoconjugates.     

Ultrastructural identification of corticotropes of the fetal rat

Corticotropes of rat fetuses aged 16, 18 and 21 days were localized by the indirect antibody-enzyme method on semithin sections of the pituitary. The development of the ultrastructure of these cells was observed on consecutive ultrathin sections. In comparison with previous data our present results show that identification of a fetal cell type cannot be based entirely on morphological criteria. The structural peculiarities of corticotropes obtained from studies in vivo are compared with those observed in cells maintained in vitro.     

Histochemistry of implantation in the rabbit

Summary The distribution of glycogen, acid and neutral mucopolysaccharides, hydrolases alkaline phosphatases, and carbohydrate dehydrogenases is described in the rabbit blastocyst and its surroundings over the implantation period from 5 to 9 days.Glycogen is found mainly in the embryonic tissues, where peaks of concentration coincide with differentiation, some is also seen in the uterine epithelium and secretion, and large quantities accumulate in the developing decidua.Neutral mucopolysaccharide is found in the yolk-sac and embryonic endoderm, and as secretion droplets in the uterine epithelium and secretion.Acid mucopolysaccharide occurs in the embryonic coverings and uterine secretion.RNA is associated in the embryo with developing tissues, and accumulates in the developing decidual cells.Hydrolases (acid phosphatase, and B esterase) increase their activity in the trophoblast knobs, in developing syncytiotrophoblast, and in the embryonic endoderm. Degeneration of the uterine epithelium is associated with maximal hydrolase activity.Trophoblastic alkaline phosphatase activity (non-specific and specific) decreases from 5 to 7 days of gestation, then increases markedly in the developing syncytiotrophoblast. AMPase appears in the embryonic mesoderm. In the uterine epithelium intense brush border staining is seen, and TPPase and UDPase become visible for a short period in the Golgi region. Phosphatases increase their activity in the decidua to 8 days and then decrease.Carbohydrate dehydrogenases (except -glycero-phosphate and -hydroxy-butyrate dehydrogenases) increase their activity in embryonic tissues, particularly in the developing syncytiotrophoblast and endoderm. Symplasma formation in the uterine epithelium is also associated with increase in enzyme activity, and a similar increase, up to 8 days of gestation, is seen in the decidua with isocitrate, malate, glucose-6-phosphate, lactate, succinate, and furfuryl alcohol dehydrogenases.Some correlation is found between the histochemical findings and the phenomena of epithelial removal, uterine secretion, decidual formation and function, giant cell function, morphogenesis, and histiotrophic nutrition, and the results are compared with previous findings for the rat in which implantation is morphologically, and probably physiologically a very different process.     

Comparative histochemical distribution of “leucine amino-peptidase” in the placenta and foetal membranes

Summary The distribution of an enzyme, or enzymes hydrolysing l-leucyl--naphthylamide is studied in the placentae, foetal membranes, and uterine structures of the horse, sheep, cat, dog, ferret, rat, rabbit, guinea-pig, and human. Activity is seen mainly in the trophoblast (except that of the cat, dog, and guinea-pig), in the rodent yolk-sac endoderm (except that of the rat), or in the uterine epithelium — surface (sheep and guinea-pig) or glandular (dog). The presence of the enzyme or enzymes is correlated with possible functions in absorption and transport of materials, or in elaboration and release of complex molecules.     

Molecular and functional analysis of the ruv region of Escherichia coli K-12 reveals three genes involved in DNA repair and recombination

Summary Recombinant plasmids carrying ruvA, ruvB, or both were constructed and used to investigate the genetic defects in a collection of UV-sensitive ruv mutants. The results revealed that efficient survival of UV-irradiated cells depends on both ruvA and ruvB, and on a third gene, ruvC, located upstream of the ruvAB operon. Southern blotting analysis was used to locate insertions in ruv and to examine putative deletion mutants. Two Tn10 insertions were located to the region encoding ruvA. Since these insertions caused a deficiency in the activities of both ruvA and ruvB, we concluded that they must exert a polar effect on ruvB. Two putative ruv deletion mutants were shown to be the result of deletion-inversion events mediated during imprecise excision of Tn10. The relevant inversion breakpoints in these mutants were located to ruvA and ruvC.