Rate of DNA Synthesis during Meiotic Prophase in Lily Microsporocytes in the Presence of Deoxyadenosine and Nalidixic Acid

The rate and period of DNA synthesis during meiotic prophasewere examined using lily microsporocytes. Meiocytes at the earlyleptotene stage were cultured for discrete periods in the presenceof inhibitors of DNA synthesis, deoxyadenosine and nalidixicacid. Deoxyadenosine, which arrests meiotic development at theearly zygotene stage, markedly suppressed DNA synthesis to 35%of control at 2 mM. Nalidixic acid simply reduced the rate ofDNA synthesis, resulting in prolongation of the synthetic period.The relevance of DNA synthesis to meiotic development is discussed. (Received January 12, 1987; Accepted May 7, 1987)     

Changes in cerebral level of monoamines by Japanese encephalitis virus infection

The changes in monoamine levels of different brain regions following Japanese encephalitis virus (JEV) intraperitoneal inoculation were examined in experimentally JEV-infected mice. In addition, virus distribution was studied using infectivity assay and immuno-histochemistry of viral antigen. 1) The level of monoamines in brain tissues was not affected by 48 hours after viral inoculation, but marked effects were elicited at 96 hours after the inoculation. The cerebral concentration of 5-hydroxyindole-3-acetic acid (5 HIAA) was increased, while that of dopamine (DA) showed a decrease. Especially these alteration were observed in the cerebral cortex, but not in the cerebellum. 2) The viral growth in the brain was observed at 48 hours after the inoculation. The growth in the cerebellum, however, was found to be lower than those in other cerebral regions. 3) The viral antigen was detected in the cerebral cortex, hippocampus, mesencephalon and diencephalon in addition to the substantia nigra and striatum. From these results, it is presumed that clinical manifestation of JEV infection may involve the changes in the metabolism of neurotransmitter, especially those of DA and serotonin in the brain.     

Identification of a novel nifH-like (frxC) protein in chloroplasts of the liverwort Marchantia polymorpha

The frxC gene, one of the unidentified open reading frames present in liverwort chloroplast DNA, shows significant homology with the nifH genes coding for the Fe protein, a component of the nitrogenase complex (Ohyama et al., 1986, Nature 322: 572–574). A truncated form of the frxC gene was designed to be over-expressed in Escherichia coli and an antibody against this protein was prepared using the purified product as an antigen. This antibody reacted with a protein in the soluble fraction of liverwort chloroplasts, which had an apparent molecular weight of 31 000, as revealed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, in good agreement with a putative molecular weight of 31945 deduced from the DNA sequence of the frxC gene. In a competitive inhibition experiment, the antigenicity of this protein was indicated to be similar to that of the over-expressed protein in E. coli. Therefore, we concluded that the frxC gene was expressed in liverwort chloroplasts and that its product existed in a soluble form. The molecular weight of the frxC protein was approximately 67 000, as estimated by gel filtration chromatography, indicating that the frxC protein may exist as a dimer of two identical polypeptides analogous to the Fe protein of nitrogenase. The results obtained from affinity chromatography supported the possibility that the frxC protein, which possesses a ATP-binding sequence in its N-terminal region that is conserved among various other ATP-binding proteins, has the ability to bind ATP.     

Endogenous beta-galactoside-binding lectin expression is suppressed in retinol-induced mucous metaplasia of chick embryonic epidermis

The fate of endogenous beta-galactoside-binding lectin of chick embryo (14K type) was investigated during the course of skin differentiation. Lectin (14K) was found in keratinized epidermis and was localized mainly in the basal and intermediate cells. However, the protein lectin in the epidermis disappeared when the cultured skin was treated with vitamin A and mucous metaplasia was observed. The synthesis of lectin mRNA was also strongly suppressed by vitamin A in a concentration-dependent manner. On the other hand, in the dermis, in which the lectin was localized in the extracellular matrix, lectin expression was scarcely affected by vitamin A. These results indicated that the lectin was expressed in the keratinized epidermis but that its expression was suppressed in vitamin A-induced mucous-secreting epithelium. The suppression may be a result of a transition of the epidermal regulatory system to one of mucous-secreting epithelium. This is the first finding that 14K lectin expression might be regulated during the course of the epidermal differentiation.     

Complete nucleotide sequence of the mitochondrial DNA from a liverwort,Marchantia polymorpha

Libraries of cosmid and plasmid clones covering the entire region of mtDNA from the liverwortMarchantia polymorpha were constructed. These clones were used for the determination of the complete nucleotide sequence of the liverwort mtDNA totally 186,608 bp (GenBank no. M68929) and including genes for 3 species of ribosomal RNAs, 29 genes for 27 species of transfer RNAs, and 30 genes for functionally known proteins (16 ribosomal proteins, 3 subunits of cytochromec oxidase, apocytochromeb protein, 3 subunits of H⁺-ATPase, and 7 subunits of NADH ubiquinone oxidoreductase). The genome also contains 32 unidentified open reading frames. Thus the complete nucleotide sequences from both chloroplast and mitochondrial genomes have been determined in the same organism. Plasmid clones are available upon the request. Gene names are represented according to Lonsdale and Leaver (1988) with modifications recommended by Lonsdale (personal communication).     

Type V collagen selectively inhibits human endothelial cell proliferation

Type V collagen from human placenta remarkably inhibited human umbilical vein endothelial cell (HUVEC) proliferation in a dose-dependent manner when coated on the culture dishes. Other types of collagen (I, III, IV) and fibronectin enhanced HUVEC proliferation under the same conditions. The inhibitory activity of type V collagen was seen not only when it was coated on the dishes, but also when it was directly added into cell culture. The attachment effect of type V collagen did not differ from that of type I collagen. The inhibitory activity is a phenomenon selective for endothelial cells, since type V collagen did not affect the proliferation of human umbilical vein smooth muscle cells, aortic smooth muscle cells, or nasal mucosa fibroblasts.     

Radiation-induced formation of apoptotic bodies in rat thymus

The process of interphase death of thymocytes in whole-body X-irradiated rats were studied. Cell size distribution analysis indicates that cell fragments (= apoptotic bodies) appeared in the thymus and increased in number depending on dose (200-1000 R) and time (2-6 hr) after irradiation with corresponding decrease in normal-size thymocytes. Occurrence of nuclear fragmentation in association with the cellular fragmentation was proved with cytofluorometric determination of DNA content in individual cells. Scanning electron microscopic observations also revealed extensive fragmentation of cells in the irradiated rat thymus. The results show clearly that cells as well as nuclei fragment rapidly into smaller pieces of various sizes in the irradiated rat thymus as commonly observed with apoptosis.