Characterization of the inhibitory effect of glucocorticoids on the DNA replication of adult rat hepatocytes growing at various cell densities

Dexamethasone inhibited the basal and EGF-stimulated DNA synthesis of adult rat hepatocytes in primary culture. The inhibition was glucocorticoid-specific: It was shown by dexamethasone and hydrocortisone, but not by progesterone, testosterone, or estradiol; and was counteracted by the glucocorticoid antagonist RU-38486 in a concentration-dependent manner. Dexamethasone acted by decreasing the rate of entry into S-phase (kG1/S), while cell cycle parameters were unaffected. The steroid was able to decrease the kG1/S severalfold even when added more than 20 hr after EGF, half-maximal effect occurring 11 hr after the addition of dexamethasone. Densely populated areas were much more sensitive to the inhibition by dexamethasone than sparsely populated areas within the same culture dish: A moderate (10 nM) concentration of dexamethasone nearly abolished the DNA synthesis in densely populated areas of hepatocyte cultures with only marginal effect on sparsely populated cells.     

Different subfamilies of alphoid repetitive DNA are present on the human and chimpanzee homologous chromosomes 21 and 22.

The alphoid repeat DNA on chimpanzee chromosome 22 was compared with alphoid repeat DNA on its human homologue, chromosome 21. Hybridization of different alphoid probes under various conditions of stringency show that the alphoid repeats of chimpanzee chromosome 22 are not closely related to those of human chromosome 21. Sequence analysis of cloned dimer and tetramer EcoRI fragments from chimpanzee chromosome 22 confirm the low overall level of homology, but reveal the presence of several nucleotide changes which are exclusive to the chromosome 21 subfamily of human alphoid DNA. Southern blot analysis of alphoid repeat DNA on the chimpanzee X chromosome suggests this subfamily has been strongly conserved during and since the separation of chimpanzee and man although the two subfamilies can be distinguished on the basis of Taq I restriction fragments.     

Chemolithotrophic growth of Desulfovibrio sulfodismutans sp. nov. by disproportionation of inorganic sulfur compounds

A new Desulfovibrio strain ThAc01 was isolated from freshwater mud; the strain conserved energy for growth under strictly anaerobic conditions by disproportionation of thiosulfate or sulfite to sulfate and sulfide according to the following reactions: $$\begin{gathered} S_2 O_3^{2 - } + H_2 O \to SO_4^{2 - } + HS^ - + H^ + \hfill \\ 4SO_3^{2 - } + H^ + {\text{ }} \to 3SO_4^{2 - } + HS^ - \hfill \\ \end{gathered}$$ Strain ThAc01 required acetate as a carbon source, but was unable to utilize acetate as an oxidizable energy source. In a defined medium with acetate and bicarbonate as carbon sources, the growth yields per mol of substrate disproportionated were 2.1 g or 3.2 g dry cell mass on thiosulfate or sulfite, respectively. Strain ThAc01 was also able to grow by dissimilatory sulfate reduction with lactate, ethanol, propanol, or butanol as electron donors and carbon sources which were incompletely oxidized to the corresponding fatty acids. However, growth by sulfate reduction was slower than by disproportionation. Elemental sulfur, nitrate, fumarate, or malate did not serve as electron acceptors. Strain ThAc01 contained desulfoviridin and cytochromes; it required panthothenate and biotin as growth factors and had a DNA base ratio of 64.1 mol% G+C. Disproportionating bacteria similar to strain ThAc01 were enriched with either thiosulfate or sulfite from various freshwater, brackish or marine mud samples. Most probable number enumeration indicated that 2×10⁶ thiosulfate-disproportionating bacteria were present per ml freshwater mud. Of various other sulfate-reducing bacteria tested, only Desulfobacter curvatus (strain AcRM3) was able to disproportionate thiosulfate or sulfite. Desulfovibrio vulgaris (strain Marburg) slowly disproportionated sulfite, but effected only a slight increase in cell density. Strain ThAc01 is proposed as the type strain of a new species, Desulfovibrio sulfodismutans.     

Coexpression of cytokeratin and vimentin in Rathke's cysts of the human pituitary gland

Summary Immunohistochemistry with monoclonal and polyclonal antibodies revealed the presence of cytokeratins in epithelial cells of Rathke's cysts in the pars intermedia of the human pituitary gland. With monoclonal antibodies specific for individual cytokeratins, the expression of CK 18, CK 8, CK 7, and CK 19 could be shown in these cells. Within the hypophysis, CK 19 and CK 7 were restricted to Rathke's cysts and a few epithelial cell clusters in the pars tuberalis, whereas other cytokeratins were also present in endocrine cells of the pars distalis. Furthermore, vimentin and, focally, glial fibrillary acidic protein (GFAP) were detected in the cystic epithelia. By double labelling, coexpression of cytokeratin and vimentin, GFAP and cytokeratin, and GFAP and vimentin could be demonstrated. Compiled data of all known cases of coexpression of cytokeratin and vimentin in normal cells reveal physiological correlations and suggest a functional significance of this rare type of coexpression of intermediate filament proteins.     

A subfamily of alphoid repetitive DNA shared by the NOR-bearing human chromosomes 14 and 22

The nucleotide sequence of members of an alpha-repeat subfamily shared by human chromosomes 14 and 22 is presented. This subfamily is organized into a higher-order repeat unit composed of a tandem repetition of an ordered array of four related but distinct 340-bp repeat dimers. An analogous situation has been described for a related but distinct subfamily shared by chromosomes 13 and 21. These two subfamilies were further shown not to be present on the homologous chimpanzee chromosomes and therefore must have arisen by rearrangement of the human genome after separation of the two species. The sequence homology between the 13/21 and the 14/22 subfamilies is about 85%. The 14/22 subfamily represents the only major alphoid DNA species on these two chromosomes and is not present elsewhere in the human genome. Fluorescent in situ hybridizations show that sequences from the 13/21 and 14/22 subfamilies can be used as specific markers for their respective chromosomes.     

Higher rate of evolution of X chromosome alpha-repeat DNA in human than in the great apes.

The rate of introduction of neutral mutations is lower in man than in other primates, including the chimpanzee. This species is generally regarded as our closest relative among the great apes. We present here an analysis of sequences of X chromosomal alphoid repetitive DNA from man and the great apes, which supports the closer relationship between man and chimpanzee and indicates a considerably increased rate of recombination in the human repeat DNA. These results indicate that the 'molecular clock' is running more quickly in man.     

Fermentation of methanethiol and dimethylsulfide by a newly isolated methanogenic bacterium

From dilution series in defined mineral medium, a marine iregular coccoid methanogenic bacterium (strain MTP4) was isolated that was able to grow on methanethiol as sole source of energy. The strain also grew on dimethylsulfide, mono-, di-, and trimethylamine, methanol and acetate. On formate the organism produced methane without significant growth. Optimal growth on MT, with doubling times of about 20 h, occurred at 30°C in marine medium. The isolate required p-aminobenzoate and a further not identified vitamin. Strain MTP4 had a high tolerance to hydrogen sulfide but was very sensitive to mechanical forces or addition of detergents such as Triton X-100 or sodium dodecylsulfate. Methanethiol was fermented by strain MTP4 according to the following equation: