Search PubMed⌕ Search

Biomedical subjects

H Nagano

Publications and source records attributed to H Nagano.

At least 199 records · Page 11Linked to original sources
PubMed1985

The fate of DNA originally existing in the zygote nucleus during achromosomal cleavage of fertilized echinoderm eggs in the presence of aphidicolin: microscopic studies with anti-DNA antibody.

In fertilized echinoderm eggs, the male and female pronuclei fuse to form the diploid nucleus even in the presence of aphidicolin, a specific inhibitor of eukaryotic DNA polymerase-alpha. The subsequent first cleavage is independent of chromosomes but dependent on spindle and amphiaster. The fate of DNA originally existing in the fused nucleus during achromosomal cleavage of fertilized sea urchin and starfish eggs induced by aphidicolin was determined using antidenatured DNA antibody. The nucleus is not formed in the divided daughter cells at the two-cell stage but the nuclear-envelope-free chromatin mass which is unassociated with mitotic apparatus remains in the center region of embryos, especially near the first cleavage furrow. These results indicate that the condensed and nonreplicated chromatin can not be associated with spindle and asters in the presence of aphidicolin.

Animals↗
PubMed1985

Inhibition of DNA replication in preimplantation mouse embryos by aphidicolin.

The regulation of trophectoderm differentiation in mouse embryos was studied by inhibiting DNA synthesis with aphidicolin, a specific inhibitor of DNA polymerase alpha. Embryos were exposed to aphidicolin (0.5 micrograms/ml) for 16 h at various preimplantation stages and scored for their ability to form a blastocyst and develop beyond the blastocyst stage. Embryos were most sensitive to aphidicolin at the late 4-cell stage and became progressively less sensitive as they developed. Aphidicolin inhibited blastocyst formation by 70%, 100%, 77%, and 24% after treatment at the 2-cell, 4-cell, noncompacted 8-cell, and compacted 8-cell stages, respectively. Although the inhibitory effect of aphidicolin on blastocyst formation decreased markedly as 8-cell embryos underwent compaction, developmental capacity beyond the blastocyst stage was poor after treatment of either noncompacted or compacted 8-cell embryos. Treatment at the morula and early blastocyst stages was less harmful to embryos than treatment at earlier stages but reduced the number of trophoblast outgrowths by interfering with hatching. Autoradiographic analysis showed that during aphidicolin treatment, incorporation of 3H-thymidine was inhibited over 90% at all stages examined, indicating an inhibition of DNA synthesis. Because inhibition of blastocyst formation by aphidicolin decreased at the compacted 8-cell stage, we suggest that approximately the first half of the fourth DNA replication cycle is critical for subsequent blastocyst formation. Furthermore, the poor further development of blastocysts formed after aphidicolin treatment of compacted 8-cell embryos suggests that the DNA replication requirements for initial trophectoderm differentiation are distinct from requirements for further development of blastocysts in vitro.

Animals↗
PubMed1984

Predominant attached state of myosin cross-bridges during contraction and relaxation at low ionic strength.

The chemical states of a cross-bridge--nucleotide complex were studied using a fluorescent ATP analogue, 1-N6-etheno-2-aza-ATP(epsilon-2-aza-ATP). The fluorescence of epsilon-2-aza-ATP at specific emission wavelengths was enhanced by 12.5 times upon binding to myosin in a relaxed muscle and the fluorescence from the resultant myosin(M)-epsilon-2-aza-ADP-Pi intermediate was 2.5 times greater than that from a M-epsilon-2-aza-ADP complex. Similar enhancements of the fluorescence of epsilon-2-aza-ATP and epsilon-2-aza-ADP were observed upon binding to heavy meromyosin in solution. Binding of F-actin did not change the fluorescence of epsilon-2-aza-ATP or epsilon-2-aza-ADP bound to heavy meromyosin. When a muscle went from a relaxed state to a state of isometric contraction or contraction with shortening, the fluorescence intensity decreased only slightly or not at all, i.e. the fluorescence of nucleotides bound to most of the myosin heads during contraction is the same as that of the M-epsilon-2-aza-ADP-Pi intermediate. These results suggest that an actomyosin(AM)-epsilon-2-aza-ADP-Pi intermediate is the predominant attached state during contraction. When the ionic strength of the relaxing solution was decreased, cross-bridges formed at 6 degrees C without tension generation. At 20 degrees C, a large tension was produced although the shortening velocity was negligibly small or zero. The fluorescence intensity decreased by 15% at 20 degrees C but only a small decrease of 3% was observed at 6 degrees C, suggesting that the predominant complexes in the attached state were AM-epsilon-2-aza-ATP and/or AM-2-aza-ADP-Pi at 6 degrees C and AM-epsilon-2-aza-ADP at 20 degrees C. Thus, the identification of the actomyosin-nucleotide complexes existing before and after the force-generating step lent further support to the conclusion that the sliding force is generated by conformational changes in actomyosin when the (epsilon-2-aza-)ADP-Pi complex is bound to it.

Adenosine Diphosphate↗
PubMed1984

Adenovirus DNA synthesized in the presence of aphidicolin.

Adenovirus types 2 and 5 DNA synthesized in vivo and in vitro in the presence of aphidicolin were studied. Inhibition of adenoviral DNA synthesis by aphidicolin was only 70% even at a concentration of 30 micrograms/ml of aphidicolin, at which the cellular DNA synthesis was completely inhibited. When initiation of the viral DNA synthesis was synchronized with hydroxyurea and labeled with [3H]thymidine for 60 min, the viral DNA synthesized in the presence of 30 micrograms/ml of aphidicolin was not of full length (35 kb) but small (approximately 12 kb) by analysis of alkaline sucrose density gradient centrifugation. When initiation of the viral DNA synthesis was not synchronized, the viral DNAs ranging from full size to 12 kb were synthesized in the presence of aphidicolin, indicating that the nascent DNAs longer than about 12 kb can continue to elongate in the presence of aphidicolin. This 12 kb DNA was not derived from the degradation products of newly synthesized full size adenoviral DNA. The viral DNA synthesis was restored and the full size of adenoviral DNA was attained within 15 min following removal of aphidicolin. About 20% of the entire viral genome length from the 5'-end was not inhibited by aphidicolin, while the synthesis of interior fragments of the adenoviral DNA was markedly inhibited by aphidicolin, judging from the electrophoretic pattern on neutral agarose gel after digestion of DNA with Hind III. These results indicate that aphidicolin inhibits adenoviral DNA replication at the internal region located approximately 20-30% from both terminals.

Adenoviruses, Human↗