Evidences for the bipartite or diploid nuclei in conidia ofStreptomyces griseoflavus

Résumé 1^o L'étude cytologique a montré que les conidia deStreptomyces griseoflavus sont uninucléaires et que dans un conidium la substance chromatique a deux sphères durant la période qui précède sa maturation. 2^o L'inactivation par rayons-X des conidia donne des courbes du type «deux-coups (two-hit)». 3^o Dans le cas d'isolation des mutants biochimiques de conidia irradiés par rayons ultraviolets, on a trouvé une apparence de mutation retardée probablement à cause du délai de ségrégation. 4^o Le conidium de mutant venant d'auxotrophe par réversion comprend des unités génétiques hétérogènes.Ces quatre faits indiquent que les conidia de cette souche ont les nuclei bipartites ou diploides.     

Maintenance of visual cells in vitro

Résumé Des fragments de rétine et des cellules visuelles isolées de la grenouilleRana pipiens ont été cultivés dans la chambre de Rose. Bien qu'une dégénérescence morphologique des segments extérieurs des cellules visuelles ait été observée pendant la culture, le pouvoir de réfraction normal et la présence du pigment visuel ont été constatés dans ces segments, les segments intérieurs avec leurs noyaux étant conservés. Mais, l'intensité du pigment visuel a été plus faible que dans la rétine fraîche. Ces résultats montrent que la cellule individuelle du photorécepteur se prête à l'étude physiologiquein vitro.

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Aided by a grant from the National Society for the Prevention of Blindness.     

Measurement of blood flow by heated thermocouple with feedback controlled current

Zusammenfassung Eine neue Messmethode für Durchblutungsmessungen besteht darin, dass selbstgeregelter Strom mit Hilfe des Rückkopplungsregelungssystems für die Heizung gebraucht wird. Mit dieser Methode wird der Temperaturunterschied zwischen den geheizten und den gekühlten Kontaktplatten ganz gering und konstant gehalten, so dass der Effekt der lokalen Wärmeakkumulation, der bei Heizung mit konstantem Strom entsteht, am geprüften Gewebe wegfällt. Diese Methode hat eine höhere Linearität und bessere Anwendungsfähigkeit über weitere Durchblutungsgebiete, und sie spricht auch schneller an als die frühere Methode der Heizung mit konstantem Strom.     

Hydrogen peroxide and hydroxyl radical involvement in the activation of caspase-3 in chemically induced apoptosis of HL-60 cells

Apoptosis of HL-60 cells induced by actinomycin D, H7, or daunorubicin was shown to involve the activation of caspase-3-like protease, 2 h after the addition of these drugs, based on microassay of enzyme activity by high-performance liquid chromatography. Catalase and a spin trap, N-t-butyl--phenylnitrone, which effectively inhibited the apoptosis induced by these drugs, also inhibited the activation of caspase-3-like protease. These results suggest that hydrogen peroxide and the hydroxyl radical are common mediators of caspase-3 activation caused by these chemicals, with apparently different functional mechanisms. Based on mitochondrial activity determined by oxygen consumption, complexes I, II, and IV were inhibited by actinomycin D. H7 inhibited complexes I and IV, 1 and 1.5 h respectively, after the addition of the drug to HL-60 cells. Daunorubicin inhibited complex IV, 1.5 h after the addition of the drug to HL-60 cells. Inhibition of complex IV by actinomycin D, H7, and daunorubicin were almost fully restored by the addition of cytochrome c. The release to the cytosol of cytochrome c by these drugs was also demonstrated by Western blot analysis. Addition of catalase inhibited the depression of complex IV activity induced by actinomycin D and H7. These observations indicate a direct relationship between hydrogen peroxide and the release of cytochrome c during apoptosis caused by actinomycin D, H7, and daunorubicin. Received 24 November 2000; received after revision 2 January 2001; accepted 30 January 2001     

IFNgamma and lymphocytes prevent primary tumour development and shape tumour immunogenicity

Lymphocytes were originally thought to form the basis of a 'cancer immunosurveillance' process that protects immunocompetent hosts against primary tumour development, but this idea was largely abandoned when no differences in primary tumour development were found between athymic nude mice and syngeneic wild-type mice. However, subsequent observations that nude mice do not completely lack functional T cells and that two components of the immune system-IFNgamma and perforin-help to prevent tumour formation in mice have led to renewed interest in a tumour-suppressor role for the immune response. Here we show that lymphocytes and IFNgamma collaborate to protect against development of carcinogen-induced sarcomas and spontaneous epithelial carcinomas and also to select for tumour cells with reduced immunogenicity. The immune response thus functions as an effective extrinsic tumour-suppressor system. However, this process also leads to the immunoselection of tumour cells that are more capable of surviving in an immunocompetent host, which explains the apparent paradox of tumour formation in immunologically intact individuals.     

Whole-genome sequencing of liver cancers identifies etiological influences on mutation patterns and recurrent mutations in chromatin regulators

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related death worldwide. We sequenced and analyzed the whole genomes of 27 HCCs, 25 of which were associated with hepatitis B or C virus infections, including two sets of multicentric tumors. Although no common somatic mutations were identified in the multicentric tumor pairs, their whole-genome substitution patterns were similar, suggesting that these tumors developed from independent mutations, although their shared etiological backgrounds may have strongly influenced their somatic mutation patterns. Statistical and functional analyses yielded a list of recurrently mutated genes. Multiple chromatin regulators, including ARID1A, ARID1B, ARID2, MLL and MLL3, were mutated in ～50% of the tumors. Hepatitis B virus genome integration in the TERT locus was frequently observed in a high clonal proportion. Our whole-genome sequencing analysis of HCCs identified the influence of etiological background on somatic mutation patterns and subsequent carcinogenesis, as well as recurrent mutations in chromatin regulators in HCCs.