Human-mouse somatic cell hybrids with single human chromosome (group E): link with thymidine kinase activity

Mouse somatic cells lacking thymidine kinase were mixed in culture with human diploid cells lacking hypoxanthine guanine phosphoribosyl transferase, and hybrid cells were isolated and maintained in a selective medium containing hypoxanthine, aminopterin, and thymidine. The hybrid cells at the time of isolation had karyotypes consisting predominantly of mouse chromosomes but with one human chromosome, a submetacentric member of group E, apparently giving thymidine kinase to the hybrid cell. However, after long-term propagation in the selective medium this chromosome has been lost, although cells continue to show thymidine kinase activity as demonstrated by the incorporation of (3)H-thy-midine into DNA in the hybrid cell. The hybrid cells have only mouse electro-phoretic variants for glucose-6-phosphate dehydrogenase, lactate dehydrogenase, and malate dehydrogenase, suggesting that the human genetic loci for these enzymes are not represented in the hybrid genome and may be unlinked to that for thymidine kinase.     

Human serum albumin phenotype activation in mouse hepatoma--human leukocyte cell hybrids

Murine hepatoma cells that secreted mouse serum albumin were fused with human leukocytes that did not produce albumin. The resulting hybrids secreted both mouse and human serum albumin, as demonstrated by immuno-electrophoretic techniques. The activation of the human genome suggests that mapping genes governing specialized functions in somatic cell hybrids may be accomplished by using adifferentiated human cells as a parental line.     

Epstein-Barr virus: detection of genome in somatic cell hybrids of Burkitt lymphoblastoid cells

Somatic cell hybrids of Burkitt lymphoblastoid cells, from which Epstein-Barr virus can be recovered, were examined for the presence of virus DNA by DNA-RNA hybridization. Four clones of hybrid cells, each negative for virus antigens by immunofluorescence, contained virus DNA in varying genomic equivalents. The number of virus genome equivalents increased in the hybrid cells after induction of virus with iododeoxyuridine.     

Spermidine requirement for cell proliferation in eukaryotic cells: structural specificity and quantitation

Six structural homologs of spermidine and five of its precursor, putrescine, were studied for their ability to prevent cytostasis of cultured L1210 leukemia cells induced by alpha-difluoromethylornithine (DFMO), a specific inhibitor of putrescine biosynthesis. High-performance liquid chromatography and competition studies with spermidine indicated that the homologs, which vary in the length of the carbon chain separating the amines, penetrated the cells. The structural specificity of the spermidine carrier was defined. Three of the six spermidine homologs supported cell growth during a 48-hour incubation in the presence of DFMO, indicating that a two-carbon extension of spermidine structure was tolerated for biological function. Two of the five putrescine homologs supported growth after being converted by the cells to their respective spermidine homologs. The central nitrogen of spermidine appears to be essential for function since diamines of chain length comparable to that of spermidine did not prevent DFMO cytostasis. No more than 15 percent of the spermidine normally present in L1210 cells was required for cell proliferation in the presence of DFMO.     

Diabetes, a new mutation in the mouse

Diabetes (db), which occurred in an inbred strain of mouse, is inherited as a unit autosomal recessive and is characterized by a metabolic disturbance resembling diabetes mellitus in man. Abnormal deposition of fat at 3 to 4 weeks of age is followed shortly by hyperglycemia, polyuria, and glycosuria. Accompanying morphological changes in the islets of Langerhans suggest neogenesis to compensate for insulin depletion.     

Cribriform degeneration (cri): a new recessive neurological mutation in the mouse

The mutation cribriform degeneration (cri) occurred in the DBA/2J strain; it is in linkage group VIII, 31 recombination units from b. Homozygotes show severe vacuolar degeneration in white and gray matter of the spinal cord and brainstem, normocytic anemia at birth which decreases in severity with age, and abnormalities of electrolyte distribution.     

离子束辐照对鼠伤寒沙门氏菌（LT_2）生物存活和营养缺陷突变的影响

本文研究了离子束辐照对鼠伤寒沙门氏菌（ＬＴ２）生物存活和营养缺陷突变的影响，并和６０Ｃｏ─ｒ射线进行比较。结果表明：在平均致死率相近的情况下，离子束辐照相对于６０Ｃｏ—ｒ射线具有损伤轻、诱变效率高的特点。     

朊蛋白多肽PrP 106-126对小鼠成神经瘤细胞N2a的毒性研究

采用Annexin V-FITC/PI双重染色的流式细胞检测和细胞凋亡的形态学观察,探讨了朊蛋白多肽PrP106-126对小鼠成神经瘤细胞系N2a细胞的毒性作用.结果表明:15、25和50μmol/L浓度的PrP 106-126作用于N2a细胞24 h均引起了细胞明显的形态学变化,提高了细胞凋亡率(P＜0.05),且浓度越大,凋亡效果越明显;在浓度为25μmol/L时,PrP 106-126作用N2a细胞48 h引起的毒性作用明显大于24 h,而100μmol/L PrP 106-126作用N2a细胞12 h并未引起细胞凋亡(P＞0.05).试验还表明PrP 106-126对神经细胞产生的毒性是淀粉样纤维物质作用细胞逐渐造成的结果.     

Immunocompetent cells among mouse thymocytes: a minor population

Suspensions prepared from thymuses of TL(+) mice contain a majority of TL(+) cells and a minority of TL(-) cells. The graft versus host reactivity of the TL(-) population is much greater than that of the whole population, as judged by the numbers of cells required to give splenic enlargements in Simonsen's assay. It is proposed that the TL(-) thymocyte represents a stage in the differentiation of TL(+) thymocytes into immunocompetent lymphocytes.     

Ascorbic acid: a culture requirement for colony formation by mouse plasmacytoma cells

Plasmacytoma stem cells explanted from mice formed colonies in culture only in the presence of L-ascorbic acid; this vitamin was not needed for the formation of granulocytic colonies. Isomers of L-ascorbic acid with less antiscorbutic activity also promoted plasmacytoma colony formation, but less effectively. Other redox compounds without antiscorbutic activity and an antioxidant were ineffective.     

The fragile X site in somatic cell hybrids: an approach for molecular cloning of fragile sites

Fragile X syndrome is a common form of mental retardation associated with a fragile site on the human X chromosome. Although fragility at this site is usually evident as a nonstaining chromatid gap, it remains unclear whether or not actual chromosomal breakage occurs. By means of somatic cell hybrids containing either a normal human X or a fragile X chromosome and utilizing two genes that flank the fragile site as markers of chromosome integrity, segregation of these markers was shown to be more frequent if they encompass the fragile site under appropriate culture conditions. Hybrid cells that reveal marker segregation were found to contain rearranged X chromosomes involving the region at or near the fragile site, thus demonstrating true chromosomal breakage within this area. Two independent translocation chromosomes were identified involving a rodent chromosome joined to the human X at the location of the fragile site. DNA analysis of closely linked, flanking loci was consistent with the position of the breakpoint being at or very near the fragile X site. Fragility at the translocation junctions was observed in both hybrids, but at significantly lower frequencies than that seen in the intact X of the parental hybrid. This observation suggests that the human portion of the junctional DNA may contain part of a repeated fragility sequence. Since the translocation junctions join heterologous DNA, the molecular cloning of the fragile X sequence should now be possible.     

SCAMP2与Rab8a在小鼠原代巨噬细胞源性泡沫细胞胆固醇转运中的作用

目的 探讨分泌载体膜蛋白2(SCAMP2)与GTP酶Rab8a在小鼠原代腹腔巨噬细胞源性泡沫细胞胆固醇转运中的相互作用.方法 8周龄雄性C57BL/6NJ小鼠提取腹腔巨噬细胞,加入50 mg/L乙酰化低密度脂蛋白(acLDL)诱导48 h,建立巨噬细胞源性泡沫细胞模型;加入10 mg/L载脂蛋白A-1(apoA-1)1...     

Carbon-13 depletion in a hydrothermal vent mussel: suggestion of a chemosynthetic food source

Tissues of a mytilid mussel from the Clambake I hydrothermal vent in the Galápagos Rift zone are strikingly depleted in carbon-13 relative to the tissues of other marine organisms. The stable carbon isotope composition of this mussel suggests that chemoautotrophic bacteria present in the hydrothermal waters are a major food source for filter-feeding organisms in this abyssal environment.     

Activation of a c-K-ras oncogene by somatic mutation in mouse lymphomas induced by gamma radiation

Mouse tumors induced by gamma radiation are a useful model system for oncogenesis. DNA from such tumors contains an activated K-ras oncogene that can transform NIH 3T3 cells. This report describes the cloning of a fragment of the mouse K-ras oncogene containing the first exon from both a transformant in rat-2 cells and the brain of the same mouse that developed the tumor. Hybrid constructs containing one of the two pieces were made and only the plasmid including the first exon from the transformant gave rise to foci in NIH 3T3 cells. There was only a single base difference (G----A) in the exonic sequence, which changed glycine to aspartic acid in the transformant. By use of a synthetic oligonucleotide the presence of the mutation was demonstrated in the original tumor, ruling out modifications during DNA-mediated gene transfer and indicating that the alteration was present in the thymic lymphoma but absent from other nonmalignant tissue. The results are compatible with gamma radiation being a source of point mutations.     

Polymorphism of sickle cell hemoglobin aggregates: structural basis for limited radial growth

Fibers composed of molecules of deoxygenated sickle cell hemoglobin are the basic cause of pathology in sickle cell disease. The hemoglobin molecules in these fibers are arranged in double strands that twist around one another with a long axial repeat. These fibrous aggregates exhibit a pattern of polymorphism in which the ratio of their helical pitch to their radius is approximately constant. The observed ratio agrees with an estimate of its value calculated from the geometric properties of helical assemblies and the degree of distortion that a protein-protein interface can undergo. This agreement indicates that the radius of an aggregate is limited by the maximum possible stretching of double strands. The geometric properties limiting the radial extent of sickle hemoglobin fibers are fundamental to all cables of protein filaments and could contribute to the control of diameter in other biological fibers such as collagen or fibrin.     

Costs and benefits of high mutation rates: adaptive evolution of bacteria in the mouse gut

We have shown that bacterial mutation rates change during the experimental colonization of the mouse gut. A high mutation rate was initially beneficial because it allowed faster adaptation, but this benefit disappeared once adaptation was achieved. Mutator bacteria accumulated mutations that, although neutral in the mouse gut, are often deleterious in secondary environments. Consistently, the competitiveness of mutator bacteria is reduced during transmission to and re-colonization of similar hosts. The short-term advantages and long-term disadvantages of mutator bacteria could account for their frequency in nature.