Common antigens of mouse oval and biliary epithelial cells. Expression on newly formed hepatocytes

Two antigens - A6 and G7 - shared by mouse biliary epithelial and oval cells were revealed by monoclonal antibodies raised in rat immunized with oval-cell-enriched liver fraction. Oval cells were induced in CBA or F1 (CBA x C57BL6) mice by a combination of a single injection of the alkylating drug Dipin with partial hepatectomy. In normal liver A6 antigen was localized, using light and electron microscopy, in biliary epithelial cells of all ducts including Hering canals. Some bile ductal and Hering cells were A6-negative. Occasionally, A6 antigen was present in single hepatocytes forming the periportal ends of hepatic cords. In preneoplastic and tumorous liver A6 antigen was present in bile ductal and oval cells and in a fraction of newly formed hepatocytes and tumor cells. G7 antigen was revealed in normal, precancerous and tumorous liver in biliary epithelial and oval cells but not in hepatocytes. A6 and G7 antigens were not liver-specific: they were expressed in various normal organs and tissues, especially in epithelia. In studies of mouse liver lineages A6 antigen can be used as a common marker of biliary epithelial and oval cells and hepatocytes at certain stages of differentiation. G7 antigen is a marker of oval and biliary epithelial cells. There was a striking similarity in A6 antigen localization to that of human blood group antigens in normal liver and liver tumors. A6 antigen may thus provide a useful tool for the study of neoexpression of human blood group antigens in liver tumors.     

Transposition of mobile genetic elements in interspecific hybrids of Drosophila

In situ hybridization of labeled DNA of four mobile dispersed genetic elements (mdg), isolated from D. melanogaster and C. virilis genomes, with polytene chromosomes of the larvae of several Drosophila species has been carried out. The data show that the mdg elements exhibit a high degree of species specificity. The same conclusions are derived from filter hybridization using ³²P-labeled D. melanogaster and D. virilis DNA and cloned mdg sequences immobilized on nitrocellulose filters. We attempted to induce transpositions (jumping) of mdg elements specific for D. virilis chromosomes to the chromosomes of related species (e.g. D. littoralis Meigen) originally lacking the representatives of this family of repeats. For this purpose we produced hybrid stocks with synthetic karyotoypes characterized by different combinations of D. virilis homologous chromosomes and hybrid chromosomes. In one of such stocks we did find by in situ hybridization the insertion of a D. virilis mdg element into the fifth chromosome of D. littoralis Meigen. The transposition (jumping) took place in the only region where somatic pairing between the fifth chromosomes of D. virilis and D. littoralis occurs more or less regularly in the hybrids. Since crossing-over in hybrid chromosomes of males is excluded in such synthetic stocks, gene conversion may be responsible for this transposition. The possible bearing of the phenomenon observed on the problem of hybrid dysgenesis is discussed.     

Karyotaxonomical studies in theJuncus bufonius aggregate in Slovakia

Karyotaxonomical investigations into theJuncus bufonius aggregate in Slovakia revealed the existence of three cytodemes, namely 2n=34, 2n=c. 72, 2n=c. 100–110.     

Receptor-mediated endocytosis and nuclear transport of a transfecting DNA construct

A soluble construct consisting of a plasmid carrying the gene of the SV40 large T-antigen and an insulin-poly-L-lysine conjugate is able to selectively transfect PLC/PRF/5 human hepatoma cells which possess insulin receptors. Transfection can be efficiently competed by excess free insulin. To examine intracellular transport of the construct, it was fluorescently labeled and its accumulation on and in cells visualized by video-enhanced microscopy and quantitative confocal laser scanning microscopy. After 2 h at 37 degrees C, the labeled construct was found predominantly in intracellular acidic compartments, with a substantial portion of fluorescence localized both near and in the cell nucleus. Binding, endocytosis, and nuclear localization of the labeled conjugate could all be competed by excess free insulin, thus indicating that entry of the conjugate into cells was specifically mediated by the insulin receptor.     

Biological activities of human interferon and 2′–5′ oligoadenylates in plants

Exogenous human interferon 2 (IFN) and 2–5 oligoadenylates (2–5A) have been shown to cause at least a dual physiological effect in tobacco and wheat: (i) increased cytokinin activity and (ii) induced synthesis of numerous proteins, among which members of two groups of stress proteins have been identified, namely pathogenesis-related (PR) and heat shock (HS) proteins. These effects were observed only by low concentrations of these substances: IFN at 0.1–1 u/ml and 2–5A at 1–10 nM.