Abstract
Inbred strains of mice vary considerably in their radiosensitivity and tumor susceptibility. BALB/c mice are particularly sensitive to the lethal and tumorigenic effects of radiation. Recent studies indicate that this phenotype may be due to a deficiency in DNA repair capacity. Recently established cultures of BALB/c kidney cells show markedly reduced double strand break rejoining activity and reduced level and activity of DNA-dependent protein kinase, an enzyme important in non-homologous end joining. It is likely that the DNA repair deficiency of BALB/c mice represents a quantitative genetic trait determined by the interactions of various sensitivity and resistance alleles.
Okayasu R, Suetomi K, Yu Y, Sliver A, Bedford JS, Cox R, Ullrich RL: A deficiency in DNA repair and DNA-PKcs expression in the radiosensitive BALB/c mouse. Cancer Res
Cloning by nuclear transplantation into pre-activated oocysts followed by transfer into surrogate recipients is readily accomplished in ruminants. However, the same techniques have been much less successful in the pig. This is partly because maintenance of pregnancy in the pig requires that more than 4 viable embryos be present. An optimized technique for cloning in pigs was recently reported by investigators from the United States and the United Kingdom. Important features of their system were a 2-stage nuclear transfer procedure, the use of granulosa cells as nuclear donors, transfer of large numbers of reconstituted embryos into each recipient, and treatment of recipients with pregnant mare serum gonadotropin and human chorionic gonadotropin to maintain pregnancy. Of 7 recipients, 2 became pregnant and 1 maintained the pregnancy to term, delivering 5 healthy piglets. In combination with gene targeting technologies these techniques will be useful for creating genetically modified pigs for the production of compatible pig organs for human transplantation.
Polejaeva IA, Chen S-H, Vaught TD, Page RL, Mullins J, Ball S, Dai Y, Boone J, Walker S, Ayares DL, Colman A, Campbell KHS: Cloned pigs produced by nuclear transfer from adult somatic cells. Nature
Double immunostaining is increasingly employed in diagnostic and investigative pathology. Serious technical problems arise when 2 monoclonal antibodies of identical IgG subclass are used. A new technique for overcoming these problems is based on the Animal Research Kit (ARK) from Dako. Briefly, the first antibody applied to the tissue is an unlabeled mouse monoclonal; this is detected with horseradish peroxidase-labeled EnVision reagent. Blocking is then carried out with normal mouse serum, and the second antibody, biotinylated using the ARK kit, is applied. This antibody is detected with alkaline phosphataselabeled streptavidin. Alkaline phosphatase activity is visualized with Fast Blue, then horseradish peroxidase activity with AEC. This technique produces background-free double staining. Only 8 antibody combinations have been tested with this protocol. In all cases, good staining was obtained, with staining patterns for each antibody comparable to that seen with single staining. This technique will work with all IgG subclasses of antibody and eliminates the need to obtain conjugated primary antibodies from commercial sources.
van der Loos CM, Gobel H: The animal research kit (ARK) can be used in a multistep double staining method for human tissue specimens. J Histochem Cytochem
Influenza A viruses cause serious respiratory and systemic disease in mammals and domestic poultry. Wild birds serve as an enormous reservoir of influenza A viruses evolutionarily related to those of mammals; however, avian to mammalian transmission appears to be limited by host-range restrictions. Pig tissue can be infected with both avian and mammalian influenza viruses, thus it has been proposed that pigs may serve as intermediate hosts for the adaptation of avian viruses to mammalian hosts. A recent report from Canada seems to confirm this relationship. In the fall of 1999, an H4N6 influenza A virus was isolated from pigs with pneumonia. Based on DNA sequence, this virus was shown to be wholly of avian origin. The most likely source of the virus was waterfowl in a nearby lake.
Karasin AI, Brown IH, Carman S, Olsen CE: Isolation and characterization of H4N6 avian influenza viruses from pigs with pneumonia in Canada. J Virol
Since its identification in cattle in the United Kingdom, bovine spongiform encephalopathy (BSE) has been linked to disease in felines, wild ungulates, and humans. However, it is not clear if BSE has spread to sheep. It is possible that BSE has been misdiagnosed as scrapie, the spongiform encepalopathy of sheep. A recent epidemiologic report in Nature suggests that BSE has not caused an epidemic of spongiform encephalopathy in sheep. Based on a postal survey of 11,554 sheep farms, there was no peak of scrapie-like disease in sheep before, during, or after the outbreak of BSE in cattle. Instead, there has been a gradual linear increase in scrapie over the last 36 years. Farms with both cattle and sheep showed no increased risk of scrapie in sheep and there was no correlation between scrapie and BSE incidences on a regional basis. This study does not allow the conclusion that BSE does not affect sheep, only that the outbreak of BSE in cattle was not associated with an epidemic of spongiform encephalopathy in sheep.
Gravenor MB, Cox DR, Hoinville LJ, Hoek A, McLean AR: Scrapie in Britain during the BSE years. Nature
There is increasing evidence that stem cells with substantial developmental potential persist into the adult. In a recent article in Science, it was reported that oligodendrocyte precursor cells (OPCs), which can be found in the adult central nervous system, could be purified, grown in culture, and induced to revert to multipotential stem cells. Reversion was stimulated by sequential culture in platelet-derived growth factor, fetal calf serum or bone morphogenetic proteins, and basic fibroblast growth factor. Once OPCs had reverted, they could be induced to differentiate into neurons, astrocytes, and oligodendrocytes by manipulating the extracellular milieu. These findings indicate that some precursor cells may retain considerable plasticity and may be reprogrammed in culture to become true stem cells.
Kondo T, Raff M: Oligodendrocyte precursor cells reprogrammed to become multipotential CNS stem cells. Science