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71.
72.
Kubota Y Takisawa H 《BioEssays : news and reviews in molecular, cellular and developmental biology》2003,25(4):313-316
Under certain conditions, the cell cycle can be arrested for a long period of time. Vertebrate oocytes are arrested at G(2) phase, while somatic cells arrest at G(0) phase. In both cells, nuclei have lost the ability to initiate DNA synthesis. In a pair of recently published papers,[1,2] Méchali and colleagues and Coué and colleagues have clarified how frog oocytes prevent untimely DNA synthesis during the long G(2) arrest. Intriguingly, they found only Cdc6 is responsible for the inability of immature oocytes to replicate DNA. Cdc6 is a key component for replication licensing, and for G(0) cells to re-enter the proliferative stage. Strikingly similar strategies for preventing the untimely replication in both cells suggest that the suppression of replication licensing is a universal mechanism for securing the prolonged arrest of the cell cycle. 相似文献
73.
Gross structural changes and neuropil formation in the brain during development were described in Idiosepius paradoxus, a sepioid that we chose as a model cephalopod. The brain originates in 4 pairs of ectodermal placodes, which occur separately in the embryonic surface undergoing epiboly. In the final period of epiboly, neuroblasts internalize from the placodes and gather into 4 pairs of ganglionic masses. The ganglionic masses assemble into a ring-like cluster encircling the inner yolk and the foregut anlage, gradually integrated into the 4 domains of a massive brain, a subesophageal mass (SBM), a supraesophageal mass (SPM), and a pair of optic lobes. In the early brain, neuropil forms a framework composed of a longitudinal ladder lying in the SBM, and a transverse arch standing on the lateral sides of the SBM and crossing the SPM. Differentiation of brain lobes proceeds from ventral to dorsal along this framework; first the magnocellular lobes and the posterior pedal lobe appear first in the SBM, the other lobes in the SBM and the basal lobes follow in the proximal region of the SPM, and the accessory lobes develop last in the most dorsal zone of the SPM. In the hatchlings, the brain lobes show almost the same arrangement as in the adults, but the accessory lobes, particularly the vertical lobe, are much smaller than those in the adults. Comparison of the present results with those in the teuthoid and the octopod indicates that developmental sequences of the brain are highly conserved in the coleoid cephalopods. 相似文献
74.
75.
Yumiko Nakagaito Motonobu Satoh Haruhiko Kuno Toshi Iwama Masao Takeuchi Akira Hakura Touho Yoshida 《In vitro cellular & developmental biology. Animal》1998,34(7):585-592
Summary We have established a multipotent clonal cell line, named MEB5, from embryonic mouse forebrains after the infection of a retrovirus
carrying E7 oncogene of human papillomavirus type 16. MEB5 cells proliferated in serum-free, epidermal growth factor (EGF)-supplemented
medium. They expressed markers for neural precursor cells (nestin, A2B5, and RC1) and did not express markers for neurons
(class III β-tubulin), astrocytes (glial fibrillary acidic protein), and oligodendrocytes (galactocerebroside). MEB5 cells
were stably maintained in an undifferentiated state with a diploid karyotype in the presence of EGF. When they were deprived
of EGF, about 50% of the cells died due apoptosis within 24 h. The remaining cells differentiated into neurons, astrocytes,
or oligodendrocytes within 2 wk. The newly developed cells with neuronal morphology were immunoreactive for γ-aminobutyric
acid and exhibited neuronal electrophysiological properties. When MEB5 cells were treated with leukemia inhibitory for 7 d,
they were induced to differentiate exclusively into astrocytes. These results inducate that MEB5 is a cell line with characteristics
of EGF-dependent, multipotent neural precursor cells. This cell line should provide a good model system to study the mechanisms
of survival, proliferation, and differentiation of the multipotent precursor cells in the central nervous system. 相似文献
76.
77.
Oku H Futamori N Masuda K Shimabukuro Y Omine T Iwasaki H 《Bioscience, biotechnology, and biochemistry》2003,67(10):2106-2114
It was found that the partially purified beta-ketoacyl-ACP synthase of Bacillus insolitus did not require the addition of FabD (malonyl-CoA:ACP transacylase, MAT) for the activity assay. This study therefore examined the necessity of FabD protein for in vitro branched-chain fatty acid (BCFA) biosynthesis by crude fatty acid synthetases (FAS) of Bacilli. To discover the involvement of FabD in the BCFA biosynthesis, the protein was removed from the crude FAS by immunoprecipitation. The His-tag fusion protein FabD of Bacillus subtilis was expressed in Escherichia coli and used for the preparation of antibody. The rabbit antibody raised against the expressed fusion protein specifically recognized the FabD in the crude FAS of B. subtilis. Evaluation of the efficacy of the immunoprecipitation showed that a trace of FabD protein was present in the antibody-treated crude FAS. However, this complete removal of FabD from the crude FAS did not abolish its BCFA biosynthesis, but only reduced the level to 50-60% of the control level for acyl-CoA primer and to 80% for alpha-keto-beta-methylvalerate primer. Furthermore, the FabD concentration did not necessarily correlate with the MAT specific activity in the enzyme fractions, suggesting the presence of another enzyme source of MAT activity. This study, therefore, suggests that FabD is not the sole enzyme source of MAT for in vitro BCFA biosynthesis, and implies the existence of a functional connection between fatty acid biosynthesis and another metabolic pathway. 相似文献
78.
Isolation and characterization of a sulfur-oxidizing chemolithotroph growing on crude oil under anaerobic conditions 总被引:1,自引:0,他引:1
Molecular approaches have shown that a group of bacteria (called cluster 1 bacteria) affiliated with the epsilon subclass of the class Proteobacteria constituted major populations in underground crude-oil storage cavities. In order to unveil their physiology and ecological niche, this study isolated bacterial strains (exemplified by strain YK-1) affiliated with the cluster 1 bacteria from an oil storage cavity at Kuji in Iwate, Japan. 16S rRNA gene sequence analysis indicated that its closest relative was Thiomicrospira denitrificans (90% identity). Growth experiments under anaerobic conditions showed that strain YK-1 was a sulfur-oxidizing obligate chemolithotroph utilizing sulfide, elemental sulfur, thiosulfate, and hydrogen as electron donors and nitrate as an electron acceptor. Oxygen also supported its growth only under microaerobic conditions. Strain YK-1 could not grow on nitrite, and nitrite was the final product of nitrate reduction. Neither sugars, organic acids (including acetate), nor hydrocarbons could serve as carbon and energy sources. A typical stoichiometry of its energy metabolism followed an equation: S(2-) + 4NO(3)(-) --> SO(4)(2-) + 4NO(2)(-) (Delta G(0) = -534 kJ mol(-1)). In a difference from other anaerobic sulfur-oxidizing bacteria, this bacterium was sensitive to NaCl; growth in medium containing more than 1% NaCl was negligible. When YK-1 was grown anaerobically in a sulfur-depleted inorganic medium overlaid with crude oil, sulfate was produced, corresponding to its growth. On the contrary, YK-1 could not utilize crude oil as a carbon source. These results suggest that the cluster 1 bacteria yielded energy for growth in oil storage cavities by oxidizing petroleum sulfur compounds. Based on its physiology, ecological interactions with other members of the groundwater community are discussed. 相似文献
79.
Summary The genetic determinant for pyocin AP41, a bacteriocin produced by Pseudomonas aeruginosa, has been cloned. The determinant is located on the chromosome flanked by a pair of inverted repeats, forming a transposon-like structure (TnAP41). TnAP41 possesses some features characteristic of the Tn3 family of transposons. Based on a comparison with the structure of the corresponding region of the chromosome of a nonproducer strain, we propose that P. aeruginosa has acquired pyocinogeny by the transposition of TnAP41 into the chromosome. The determinant comprises two ORFs encoding the protein subunits responsible for the killing action (the large component) and immunity (the small component). Amino acid sequences of the C-terminus of the large component (the deoxyribonuclease domain) and the immunity protein show remarkable homology to those of E2 group colicins, suggesting that these bacteriocins, which are produced by distantly related species, have originated from a common ancestor. 相似文献
80.
Sagi K Fujita K Sugiki M Takahashi M Takehana S Tashiro K Kayahara T Yamanashi M Fukuda Y Oono S Okajima A Iwata S Shoji M Sakurai K 《Bioorganic & medicinal chemistry》2005,13(5):1487-1496
An inhibitor of the complex of factor VIIa and tissue factor (fVIIa/TF), 2-substituted-4-amidinophenylpyruvic acid 1a, was structurally modified with the aim of increasing its potency and selectivity. The lead compound 1a was originally found in our factor Xa (fXa) inhibitor library on the basis of structural similarity of the primary binding sites of fVIIa and fXa. The design was based on computational docking studies using the extracted active site of fVIIa. Compound 1j was found to inhibit factor VIIa/TF at nanomolar concentration with improved selectivity versus fXa and thrombin and it preferentially prolonged the clotting time in the TF-dependent extrinsic pathway. 相似文献