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Volume 16 (1991)
- Issue 6 Pages 433-
- Issue 5 Pages 357-
- Issue 4 Pages 273-
- Issue 3 Pages 189-
- Issue 2 Pages 113-
- Issue 1 Pages 1-
Volume 16, Issue 2
Displaying 1-9 of 9 articles from this issue
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Yuichi Hashimoto1991 Volume 16 Issue 2 Pages 113-123
Published: 1991
Released on J-STAGE: March 27, 2006
JOURNAL FREE ACCESSRetinoids (retinoic acid and its analogs) are widely involved in the control of cell proliferation, cell differentiation and embryonic development. A series of potent and novel synthetic retinoids named retinobenzoic acids has been developed. Retinobenzoic acids have proven to be useful tools in the investigation of the molecular mechanisms of retinoidal actions. Retinoids elicit their biological effects by binding to and activating specific nuclear receptors for retinoids (RAR's) which belong to the steroid/thyroid nuclear receptor superfamily. Recent investigations concerning the structure and function of nuclear receptors, namely of RAR's, are reviewed. Three subtypes of RAR (RAR-α, RAR-β and RAR-γ) have been identified so far. Each RAR is considered to play particular roles in the retinoidal actions. The role of each RAR is discussed in relation to their features and to the structure-activity relationships of retinoids. RAR's act as retinoid-dependent transcription factors which bind to a specific site of the gene and control its expression. Recent progress in the investigation of the interaction of RAR's with the responsive genes and with nuclear co-factors is reviewed. The diversity of retinoidal actions are possibly explained by the diversity of RAR's in their structure and in their spatial and temporal distribution, by the diversity of base sequences which interact with RAR's, by the diversity of cell type-specifically determined hierarchy of gene expression, and by the diversity of the nuclear factors which interact with RAR's.View full abstractDownload PDF (1048K) -
Mikako T. Oka, Takao Arai, Yukihisa Hamaguchi1991 Volume 16 Issue 2 Pages 125-134
Published: 1991
Released on J-STAGE: March 27, 2006
JOURNAL FREE ACCESSIn the mitotic sea urchin egg, the spindle microtubules were composed of different tubulin isotypes from those of astral microtubules using monoclonal antibodies [Oka et al. (1990) Cell Motil. Cytoskeleton, 16, 239-250]. Three of the antibodies, D2D6, DM1B, and YL1/2, were specific for spindle microtubules, astral microtubules and reactive with both microtubules, respectively. The mitotic sea urchin egg was treated with microtubule depolymerizing (colcemid and nocodazole) and stabilizing (hexylene glycol) drugs and change in the heterogeneous distribution of the tubulin isotypes was investigated by the immunofluorescence procedure using these three monoclonal anti-tubulin antibodies. We observed that: (1) the microtubule depolymerizing drugs caused quick depolymerization of most mitotic microtubules, and a small number of spindle microtubules remaining were stained with all three antibodies; (2) hexylene glycol induced many microtubules in the mitotic apparatus, which was stained with D2D6 but was not stained with DM1B; (3) hexylene glycol also induced a great number of miniasters in the cytoplasm, and they were stained with three antibodies. These results suggest that these drugs altered the distribution of tubulin isotypes in the mitotic microtubules during depolymerisation or polymerization within a short time.View full abstractDownload PDF (1767K) -
Yokichi Hayashi, Alfred Reszka, Taisen Iguchi, Barb Reinish, Takuji Ka ...1991 Volume 16 Issue 2 Pages 135-139
Published: 1991
Released on J-STAGE: March 27, 2006
JOURNAL FREE ACCESSWe transfected rat pheochromocytoma (PC12) cells with a cDNA encoding chicken integrin β1 subunit. The chicken integrin β1 subunit produced in stable transfectants associated with two major α subunits of rat integrins to form interspecific chimeric receptors. These receptors mediated cell spreading and initial neurite outgrowth on laminin as did corresponding endogenous integrins, although they were slightly less effective in inducing cell adhesion to laminin. These results indicate that chicken integrin β1 may functionally substitute for β1 subunit of rat integrins in PC12 cells. Apparently, the structure of the integrin β1 subunit is highly conserved in the evolution of these species.View full abstractDownload PDF (622K) -
Yoshito Sadahira, Yuko Hirao, Kenzou Uehira, Tetsuo Kimoto1991 Volume 16 Issue 2 Pages 141-147
Published: 1991
Released on J-STAGE: March 27, 2006
JOURNAL FREE ACCESSWe created a monoclonal antibody, designated EB1 (IgM, kappa), that reacts with erythroblasts by fusion of P3-X63-Ag8.653 with splenocytes of rats immunized with erythroblastic islands isolated from mice spleens. Western blotting revealed that EB1 reacted with the band 3 protein of the erythrocytic membrane. It stained erythrocytes and erythroblasts, forming clusters in the bone marrow, splenic red pulp, and fetal liver, but did not stain other tissues in the cryostat sections. The EB1 antigen was detected during dimethyl sulfoxide-induced differentiation of murine erythroleukemia cells. Immunoelectron microscopy revealed that the EB1 antigen was expressed from the basophilic erythroblasts during normal erythroid differentiation. Preferential segregation of the EB1 antigen on the cell membrane of the nucleating erythroblasts was not observed. These results suggest that EB1 is specific for erythrocyte band 3 protein and may be useful for studying erythroid cell differentiation.View full abstractDownload PDF (2358K) -
Takanori Yanai, Tadashi Shimo-Oka, Ichio Ii1991 Volume 16 Issue 2 Pages 149-156
Published: 1991
Released on J-STAGE: March 27, 2006
JOURNAL FREE ACCESSSome members of the integrin family recognize the RGD sequence which is common to cell adhesive proteins in a divalent cation-dependent manner. In the presence of Ca2+ and Mg2+, the fibronectin receptor of placenta recognizes the RGD sequence of fibronectin, but not that of vitronectin, while the vitronectin receptor of placenta recognizes the RGD sequence of vitronectin, but not that of fibronectin, although both receptors recognize the same RGD sequence. We have found by performing an enzyme-linked immunosorbent assay (ELISA) using receptor-specific monoclonal antibodies and by electrophoretic analysis that in the presence of Mn2+ a vitronectin receptor of placenta binds to an affinity column coupled with the cell-binding domain of fibronectin. By replacing divalent cations from Mn2+ to Ca2+ and Mg2+, the vitronectin receptor was completely eluted from the column. When the synthetic peptides GRGDSP and GRGESP were applied to the column as competitors, the Mn2+-dependent binding was inhibited by both peptides. These results suggest that Mn2+ elicits a binding activity of the placenta vitronectin receptor to the RGD site of fibronectin. The modulation of ligand specificity by Mn2+ will provide an important clue in the elucidation of the cause of individual ligand specificity of RGD-recognizing integrins.View full abstractDownload PDF (740K) -
Tatsuma Mohri, Yukihisa Hamaguchi1991 Volume 16 Issue 2 Pages 157-165
Published: 1991
Released on J-STAGE: March 27, 2006
JOURNAL FREE ACCESSUpon fertilization, the concentration of intracellular Ca2+ (Cai) in sea urchin eggs increased up to 3 μM when measured with fura-2, a fluorescent Ca indicator and the increase in Cai traversed from the sperm entry point as a wave over the entire egg at the mean propagation velocities of 5.0 μm/sec in C. japonicus egg and 5.3 μm/sec in H. pulcherrimus egg. However, the velocity was not uniform; i.e., it was rapid in the vicinity of the sperm entry point and the opposite point, but slow in the central region of the egg. Microinjecting a Ca-EGTA buffer and an IP3 solution into the C. japonicus egg induced the transient Cai increase more rapidly than that upon fertilization, due perhaps to the diffusion of the injectates.
In order to investigate Ca2+ release during Cai increase upon fertilization, EGTA solutions were microinjected into unfertilized or fertilizing eggs. Microinjecting 100 mM EGTA (final concentration of 1 mM) not only suppressed the transient Cai increase, but also reduced the increased Cai rapidly, and never induced egg activation after insemination, whereas 10 mM EGTA (final concentration of 0.1 mM) did not significantly affect the Cai increase or the activation. Ca2+ released upon fertilization was estimated to be 150-170 μM in the egg cytoplasm from the amount of microinjected EGTA and fura-2.
It was concluded that although more than 150 μM of Ca2+ was released intracellularly upon fertilization, Cai increased to only a few μM because most of the released Ca2+ was sequestered by intracellular Ca2+ binding substances.View full abstractDownload PDF (1420K) -
Toru Yamada, Shozo Ishizaka1991 Volume 16 Issue 2 Pages 167-173
Published: 1991
Released on J-STAGE: March 27, 2006
JOURNAL FREE ACCESSIt was clearly shown that the change in thermodynamical parameters could cause the segregation of membrane protein aggregations in the phospholipid membrane. At first, reconstituted vesicles were prepared with a membrane protein, bacteriorhodopsin and a constituent phospholipid of biomembranes, L-α-dimyristoyl phosphatidylcholine. When the temperature of the suspension was decreased or the osmotic pressure was increased by adding poly(ethylene glycol) to this vesicle suspension at 23 degrees, the circular dichroism spectra showed a typical band indicating bacteriorhodopsin trimer formation implying their aggregation. This suggests that the aggregation of trimers proceeded by adding poly(ethylene glycol) into the vesicle suspension, just as it proceeded by decreasing the temperature. Next, vesicles were prepared with fluorescein isothiocyanate-labeled bacteriorhodopsin, photoemissive bacteriorhodopsin and L-α-dimyristoyl phosphatidylcholine. The excitation energy transfer between the two modified proteins was measured by fluorescence spectroscopy. In this case, however, when poly(ethylene glycol) was added into the suspension, the yield of the excitation energy transfer decreased. This result indicates that modified proteins aggregate separately in a segregated form in the vesicle membrane.View full abstractDownload PDF (606K) -
Hisato Shida, Malcolm S. Steinberg1991 Volume 16 Issue 2 Pages 175-183
Published: 1991
Released on J-STAGE: March 27, 2006
JOURNAL FREE ACCESSThe molecular constituents of desmosomes and hemidesmosomes were compared by examining bovine muzzle epidermis under immunoelectron microscopy using a postembedding method, first with antibodies prepared to four desmosomal antigens (DP1/2, DP3, DG1, DG2/3), followed by protein A-gold (PAG) complexes. The four antibodies showed almost negative labeling at hemidesmosomes as compared with the labeling observed at the desmosomes in the same tissue. By counting the number of PAG particles/200 mμ at hemidesmosomes and desmosomes, the above qualitative observation was confirmed quantitatively. These results support a new concept which has recently been proposed by several researchers that hemidesmosomes and desmosomes are immunochemically distinct.View full abstractDownload PDF (4271K) -
Yugo Habata, Hideko Urushihara, Hui Fang, Kaichiro Yanagisawa1991 Volume 16 Issue 2 Pages 185-187
Published: 1991
Released on J-STAGE: March 27, 2006
JOURNAL FREE ACCESSSexual cell fusion is an initial step of macrocyst formation in Dictyostelium discoideum and requires environmental conditions such as darkness, plenty of water and the presence of calcium ions. We have been analyzing the mechanism of sexual cell fusion between HM1 and NC4, heterothallic strains in D. discoideum. Cells of these strains have been shown to be fusion competent when cultured in a liquid medium in darkness, but not so when cultured on agar plates or in a liquid medium in the light. Two cell-surface proteins, gp70 and gpl38, have been identified as target molecules for fusion-blocking antibodies and therefore as relevant to sexual cell fusion.
In the present study, gp70 was shown to be present in HM1 cells cultured in the light, and fusion incompetent. Intact HM1 cells cultured in the light were unable to absorb the fusion-blocking activity of antibodies against membrane components of fusion-compenent HM1 cells, whose activity had been shown to be absorbed by gp70, but they did so after separation of proteins in the SDS-PAGE. In addition, fusion-competent HM1 cells were found to lose their fusion competence by subsequent cultivation in the light. This loss of competence was cycloheximide sensitive, indicating that de novo synthesis of proteins was necessary for this inhibition. From these results, we presume that light induces a protein that hinders the interaction of gp70 in HM1 cells with its receptor on the NC4 cell surface and thereby inhibits the sexual process between these strains.View full abstractDownload PDF (278K)
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