Sister-chromatid exchange induction by sodium selenite: plasma protein-bound selenium is not the active SCE-inducing metabolite of Na2SeO3.

Sodium selenite (Na2SeO3) is an anticarcinogenic/antimutagenic/anticlastogenic agent that under certain incubation conditions induces sister-chromatid exchanges (SCEs), unscheduled DNA synthesis, and chromosome aberrations. Previous work has shown that SCE induction by Na2SeO3 depends on the presence of red blood cells (RBCs). Therefore, Na2SeO3 uptake and release by RBCs was studied in the present report as was the effect of plasma protein-bound selenium, the end product of Na2SeO3 metabolism by RBCs, on the SCE frequency of purified lymphocyte cultures. Na2SeO3 uptake by human whole blood, RBCs in plasma, RBCs in fetal calf serum, and RBCs in Hanks' balanced salt solution occurs rapidly, reaching a maximum after 2 min (37 degrees C). Release of Na2SeO3 from RBCs depends on the presence of plasma proteins to which the metabolized selenium becomes bound. In spite of the fact that plasma protein-bound selenium is the major product of Na2SeO3 metabolism by RBCs, the SCE frequency of purified lymphocyte cultures was unchanged when plasma protein-bound selenium (7.90 X 10(-6) and 1.19 X 10(-5) M) was added to the medium for the final 19 h of incubation. Further study showed that Na2SeO3 could induce SCEs in blood cultures that had been washed to remove plasma proteins and incubated in medium 199, a maintenance medium lacking fetal calf serum. These findings indicate that a Na2SeO3 metabolite other than plasma protein-bound selenium is responsible for Na2SeO3's SCE-inducing ability in human whole-blood cultures.

Dependence of the sister-chromatid exchange-inducing abilities of inorganic selenium compounds on the valence state of selenium.

Inorganic selenium (Se) compounds having Se of different valence states were tested for their abilities to induce sister-chromatid exchanges (SCEs) in human whole blood cultures. The Se compounds tested (and their Se valence states) were: sodium selenide (Se(2-)), selenium dioxide (Se(4+)), selenium (Se(0)), sodium selenate (Se(6+)), and sodium selenite (Se(4+)). Human whole blood cultures were exposed to concentrations of these compounds ranging from 1.12 X 10(-6)-8.00 X 10(-5) M for the final 18 h of the 96-h incubation period. Only sodium selenate failed to induce SCEs at high concentrations. Of the 4 SCE-inducing Se compounds studied selenium was the most potent inducer of SCEs, and sodium selenite was the least effective SCE-inducing agent. The SCE-inducing abilities of the Se compounds in decreasing order of their effectiveness were: selenium > selenium dioxide > solium selenide > sodium selenite > sodium selenate.

Rubber solvent: a clastogenic agent that fails to induce sister-chromatid exchanges.

Rubber solvent was tested for its ability to induce chromosome aberrations and sister-chromatid exchanges in human whole blood cultures. Following exposure to relatively low rubber solvent concentrations (0.0125% and greater) significant increases in the frequencies of chromatid gaps and breaks were observed. At higher rubber-solvent concentrations (0.05% and greater) there were also significant increases in the frequency of chromosome breaks. In contrast to the increase in chromosome aberrations following rubber-solvent exposure, rubber-solvent concentrations up to the toxic level failed to produce increases in the sister-chromatid exchange frequency.

Sister-chromatid exchange induction by sodium selenite: dependence on the presence of red blood cells or red blood cell lysate.

Sodium selenite (Na2SeO3) sister-chromatid exchange (SCE) induction was studied in both short-term and long-term cell cultures. The ability of Na2SeO3 to induce SCEs was found to depend on the culture conditions employed. Concentrations of Na2SeO3 (7.90 X 10(-6) M and greater) that produced elevated SCE frequencies in whole blood cultures resulted in control level SCE frequencies (6-8 SCEs/cell) in Ficoll-Hypaque--purified lymphocyte cultures. However, whole blood and purified lymphocyte cultures were equally sensitive to SCE induction by methyl methanesulfonate (MMS), ethyl methanesulfonate (EMS), and N-hydroxy-2-acetylaminofluorene (N-OH-AAF). Analysis of different whole blood components showed that the presence of red blood cells (RBCs), and specifically RBC lysate, was a prerequisite for Na2SeO3 SCE induction in purified lymphocyte cultures. The SCE frequencies of xeroderma pigmentosum (XP12RO) and normal human lymphoblastoid cell lines were also found to be unaffected by Na2SeO3 concentrations that produced elevated SCE frequencies in whole blood cultures. Incubation of these latter two cell types with Na2SeO3 and RBC lysate resulted in SCE frequencies comparable to those in Na2SeO3-exposed whole blood cultures.

Effect of sodium selenite and methyl methanesulfonate or N-hydroxy-2-acetylaminofluorene co-exposure on sister-chromatid exchange production in human whole blood cultures.

Sodium selenite (Na2SeO3) was tested for its sister-chromatid exchange (SCE)-inducing ability in human whole blood cultures and for the effect of its co-exposure with methyl methanesulfonate (MMS) or N-hydroxy-2-acetylaminofluorene (N-OH-AAF) on SCE frequency. Long exposure times (77 h and 96 h) to 3.95 X 10(-6) M Na2SeO3 resulted in cell death as measured by mitotic indices, but mitotic figures were present after exposure to higher concentrations for a shorter time (19 h). High Na2SeO3 concentrations (7.90 X 10(-6) and 1.19 X 10(-5) M) resulted in a three-fold increase in the SCE frequency above background level (6--7 SCEs/cell). Exposure of lymphocytes to 1 X 10(-4) M MMS for the last 19 h of culture yielded an average SCE frequency of 30.17 +/- 0.75 while a similar exposure to 2.7 X 10(-5) M N-OH-AAF resulted in 13.61 +/- 0.43 SCEs/cell. Simultaneous addition of the high Na2SeO3 concentrations and MMS or N-OH-AAF to the cultures resulted in SCE frequencies that were 25--30% and 11--17%, respectively, below the sum of the SCE frequencies produced by the individual compounds.

Hoechst 33258 banding of Drosophila nasutoides metaphase chromosomes.

Hoechst 33258 banding of D. nasutoides metaphase chromosomes is described and compared with Q and C bands. The C band positive regions of the euchromatic autosomes, the X and the Y fluoresce brightly, as is typical of Drosophila and other species. The fluorescence pattern of the large heterochromatic chromosome is atypical, however. Contrary to the observations on other species, the C negative bands of the large heterochromatic chromosome are brightly fluorescent with both Hoechst 33258 and quinacrine. Based on differences in the various banding patterns, four classes of heterochromatin are described in the large heterochromatic chromosome and it is suggested that each class may correspond to an AT-rich DNA satellite.

125 I-labeled DNA-RNA hybrids in cytological preparations.

RNA complementary to bulk humanplacental DNA was synthesized in vitro both in the presence and absence of (3)H-labeled ribonucleotides. The (3)H-labeled RNA was used directly for hybridization to the DNA of human metaphase chromosomes, whereas the unlabeled complementary RNA was labeled chemically with (125)I before hybridization. A comparison of autoradiographs produced by either isotope revealed no qualitative differences in the chromosomal annealing sites of the same population of RNA molecules. Since (125)I-labeled nucleic acids give similar, if not identical, results as do (3)H-labeled nucleic acids in in situ hybridization experiments, their use should make possible the localization of genetic elements for which tritium labeling methods are either inadequate or not possible.