Distributions of cell populations within alpha-particle range of plutonium deposits in the rat and beagle testis

Plutonium is not uniformly distributed in testicular tissues; thus some cell populations may receive larger or smaller radiation exposures than would be expected if the nuclide were uniformly distributed. The distributions of cell populations within alpha-particle range of Pu deposits in rat and beagle testes were determined. The data were collected from autoradiographs of testicular tissues containing 241Pu. A cell distribution factor (CDF) was determined for each cell population and is defined as the average number of each cell type within alpha-particle range of each observed Pu deposit relative to the number of each cell type that would be expected within alpha-particle range of each Pu deposit, if the deposits were distributed uniformly. In addition, the percentage of the spermatogonial stem cell population within alpha-particle range of Pu deposits was determined. In rats, the CDF for the spermatogonial stem cells is about 2.2. This value is similar to other enhancement and inhomogeneity factors reported for rodents in the literature. In beagles the CDFs to all cells in the seminiferous epithelium were less than the rats. In addition, the percentage of spermatogonial cells within alpha-particle range of Pu concentrations in the interstitial tissues was a factor of about 3 less in the dog than in the rat. The largest CDFs seen in both species were in the interstitial tissues, particularly for Leydig cells. Because the organization of testicular tissues in the beagle is quite different from rodents but more similar to human, the results from this study suggest that extrapolations from rodents to humans may tend to overestimate the potential for radiation exposure to spermatogonial stem cells as well as the fraction of the spermatogonial stem cell population at risk to exposure from internally deposited 239Pu.     

Quantitation of the transgenome size in chromosome-mediated gene transfer lines

Twenty-two HPRT-selected chromosome-mediated gene transfer lines were characterized by quantitative "dot" blotting. The range of human sequences in these lines extended from over 120,000 kb to less than 5,000 kb. One-half of these lines carried less than 16,000 kb.     

Epidemiological characteristics of platelet aggregability.

The epidemiological characteristics of platelet aggregability were established in 958 participants in the Northwick Park Heart Study. The main analyses were based on the dose of adenosine diphosphate at which primary aggregation occurred at half its maximum velocity. Aggregability increased with age in both sexes, was greater in whites than blacks (particularly among men), and tended to decrease with the level of habitual alcohol consumption. Aggregability was, however, greater in women than men and in nonsmokers than smokers. There was no relation between aggregability on the one hand and obesity, current or past oral contraceptive use, menopausal state, or blood cholesterol and triglyceride concentrations on the other. Aggregability was somewhat, though not significantly, higher in men with a history of ischaemic heart disease and in those with electrocardiographic evidence of ischaemia than in those without. There was a strong association between the plasma fibrinogen concentration and aggregability. The widely held concept of platelet aggregability and its implications is probably an oversimplification. In the prevention of thrombosis it may be as useful to consider modifying external influences on platelet behaviour, such as plasma fibrinogen concentration or thrombin production, as it is to rely solely on platelet active agents.     

Polymorphism in the structure of the yeast mitochondrial tRNA synthesis locus.

Yeast mitochondrial DNA contains a genetic locus, called the tRNA synthesis locus, which codes for information necessary for mitochondrial tRNA biosynthesis. A 9S RNA molecule coded by this locus is thought to be the trans-acting element required for the removal of 5' extensions from tRNA precursors. The DNA coding for this RNA maps to a region of mitochondrial DNA known to contain strain specific restriction site polymorphisms. Comparison of the tRNA synthesis locus in two such strains by sequence analysis demonstrates that the restriction enzyme polymorphisms are due to the deletion/insertion of a 50 base pair GC-rich element in the 5' flanking sequence of the 9S RNA coding region. There are also several differences between the 9S RNA coding region of these two strains which do not interfere with the tRNA synthesis function.     

alpha-Putrescinylthymine and the sensitivity of bacteriophage phi W-14 DNA to restriction endonucleases.

The modified base alpha-putrescinylthymine (putT) in phi W-14 DNA blocks cleavage of the DNA by 17 of 32 Type II restriction endonucleases. The enzymes cleaving the DNA do so to widely varying extents. The frequencies of cleavage of three altered forms of the DNA show that putT blocks recognition sites either when it occurs within the site or when it is in a sequence flanking the site. The blocking is dependent on both charge and steric factors. The charge effects can be greater than the steric effects for some of the enzymes tested. All the enzymes cleaving phi W-14 DNA release discrete fragments, showing that the distribution of putT is ordered. The cleavage frequencies for different enzymes suggest that the sequence CAputTG occurs frequently in the DNA. Only TaqI of the enzymes tested appeared not to be blocked by putT, but it was slowed down. TaqI generated fragments are joinable by T4 DNA ligase.     

Mutation Rates for Enzyme and Morphological Loci in Barley ( HORDEUM VULGARE L.)

Spontaneous mutation rates were estimated by assaying 84,126 seedlings of a highly homozygous barley line (isogenic line 2025) for five enzyme loci. No mutants were observed in 841,260 allele replications. This result excludes, at probability level 0.95, a spontaneous mutation rate larger than 3.56 x 10^-6/locus/gamete/generation for these enzyme loci. Isogenic line 2025 also was scored for mutants at four loci governing morphological variants. No mutants were observed in 3,386,850 allele replications which indicates that the upper bound for the mutation rate for these loci is 8.85 x 10^-7. It was concluded that, even though spontaneous mutation has been important in creating variability in the barley species at the loci scored, the rate is too low to have much affect on the short-term dynamics of barley populations.     

Intermediary carbon metabolism of Azospirillum brasilense.

Azospirillum brasilense Sp 7 grew rapidly in AZO medium containing reduced nitrogen and succinate as an energy source, with a doubling time of 43 min. No growth was measured with glucose as the sole carbon source. In contrast, Azospirillum lipoferum Sp 59b could grow in media containing either succinate or glucose with a doubling time of 69 min and 223 min, respectively. Warburg-Barcroft respirometry showed that the rate of oxygen consumption by A. brasilense Sp 7 on glucose medium (0.034 mumol of O2 min-1 mg-1 of cell protein) was only one-quarter of that on succinate medium (0.14 mumol of O2 min-1 mg-1). Radioisotopic labeling showed that very little glucose was assimilated by A. brasilense Sp 7 as compared to succinate. High respiration rates were measured on A. lipoferum Sp 59b with either succinate (0.15 mumol of O2 min-1 mg-1) or glucose (0.13 mumol of O2 min-1 mg-1) as the sole carbon source. The pattern of CO2 evolution from differentially labeled succinate indicated that A. brasilense Sp 7 had a complete tricarboxylic acid cycle. Assimilation of most of the radioactivity from labeled succinate, pyruvate, and acetate into lipids suggested a strong anabolic metabolism and the presence of an active malic enzyme of phosphoenolpyruvate carboxykinase. The distribution of radioactivity from differentially labeled pyruvate showed that gluconeogenesis competed with pyruvate dehydrogenase. Uptake and incorporation of labeled acetate also indicated the presence of a glyoxylate cycle in A. brasilense Sp 7.     

Glycolipid-dependent interaction between human migration-inhibitory factor and mononuclear phagocytes

It has been previously established in the guinea pig that the response of peritoneal macrophages to migration inhibitory factor (MIF) is enhanced by a macrophage glycolipid and that gangliosides reversibly bind MIF. This suggests that glycolipids function as cell surface receptors for MIF. In this report, it is demonstrated that the response of human peripheral blood monocytes to human MIF is augmented by preincubation of these cells with glycolipidenriched material extracted from the human macrophage-like cell line U937 or human peripheral blood monocytes and with a purified glycolipid from guinea pig peritoneal macrophages. In addition, a mixed ganglioside preparation from bovine brain shows the same effect. In contrast, the pure gangliosides, G_M1 and G_D1a, and glycolipids from the HL-60 cell line, which is a MIF-unresponsive cell line, were not able to enhance the response to human MIF. The specificity of enhancement by particular glycolipids could not be attributed to an increased uptake of only enhancing glycolipids since there was no significant difference between the association of monocytes with radioactive liposomes containing biologically active or inactive glycolipids. Pronase treatment did not affect the enhancing activity of the U937 glycolipidenriched material. Incubation of cells with glycolipids results in enhancement only if done at 37 °C and not at 4 °C. Therefore, the association of lipid with the monocyte surface appears to be dependent on temperature.Further evidence for the receptor nature of these enhancing glycolipids is provided by experiments involving affinity purification experiments. Coupling of bovine brain mixed gangliosides to agarose resulted in a matrix capable of reversibly binding MIF. G_D1a-agarose was inactive in this respect.     

T and B cells induce macrophages which suppress proliferation but not lymphokine secretion

In vitro culture of mouse spleen cells for 2 days or more leads to the production of adherent, phagocytic, Thy-1-, Ia+, Lyt-2- cells ("suppressor macrophages") which strongly inhibit the proliferative response of T and B lymphocytes to a variety of stimuli: mitogens, specific antigens, and antigen-nonspecific growth factors. Suppressive activity fails to develop, however, in cultured spleen cells from which nonadherent cells have been removed before the initial 48-hr incubation, and only partial suppression is obtained from cell suspensions from which T cells have been depleted before culture. We find that the requirement for nonadherent cells can be replaced by graded doses of lymphocytes. Lyt-2- and Lyt-2+ T cells are about equally potent in inducing suppressive activity in nonadherent cells. Surprisingly, B cells (containing fewer than 0.1% contaminating T cells) are also able to induce suppression in this system. The suppression induced includes both indomethacin-sensitive and indomethacin-resistant components. Interestingly, not all stages of mitogen-induced T-cell activation are blocked by these adherent cells: proliferation is inhibited, but production of interleukin 2 (IL-2) and interleukin 3 (IL-3) is unaffected.     

Molecular cloning of DNA complementary to bovine adrenal P450scc mRNA

P450_scc is the rate-limiting hormonally regulated enzyme that cleaves the cholesterol side chain. Translation of bovine adrenocortical mRNA and immunoprecipitation with rabbit anti-bovine P450_scc indicates P450_scc mRNA represents 1% of the total. DNA complementary to bovine adrenocortical mRNA was cloned in the $\text{PstI}$ site of pBR322 by dC·dG tailing and high-efficiency transformation. A clone containing sequences complementary to P450_scc mRNA was identified by hybrid-selected translation only when plasmid DNA was first purified by CsCl gradient centrifugation. As is often the case with hybrid-selected translation, the clone identified contains a small insert.