Achromosomal cleavage of fertilized starfish eggs in the presence of aphidicolin

Nagano, Hiroshi; Hirai, Setsuro; Okano, Kiyoshi; Ikegami, Susumu

doi:10.1016/0012-1606(81)90272-4

Cited by 83 publications

(52 citation statements)

References 9 publications

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“…Unlike the ordinary somatic cell cycle, however, a functional cell cycle checkpoint is lacking in the early embryonic cell cycle of some organisms, including frog (Newport and Dasso, 1989), starfish and some sea urchins (Yamada et al, 1985). In starfish, when DNA replication is inhibited, the early embryonic cell cycle can progress with M phase cycling without S phase (Nagano et al, 1981) (Fig. 2).…”

Section: Control Of the Embryonic Cell Cycle Order Without Checkpointsmentioning

confidence: 99%

Start of the embryonic cell cycle is dually locked in unfertilized starfish eggs

et al. 2009

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A key event in the oocyte-to-embryo transition is the start of the embryonic mitotic cell cycle. Prior to this start, the cell cycle in oocytes is generally arrested at a particular stage during meiosis, and the meiotic arrest is released by fertilization. However, it remains unclear how release from the meiotic arrest is implicated in the start of the embryonic cell cycle. To elucidate this link, we have used starfish eggs, in which G1 phase arrest occurs after completion of meiosis if the mature oocytes are not fertilized, and fertilization simply directs the start of the embryonic cell cycle. The starfish G1 arrest is known to rely on the Mos-MAPK-Rsk (p90 ribosomal S6 kinase) pathway, and inactivation of Rsk induces S phase in the absence of fertilization. However, here we show that this S phase is not followed by M phase when MAPK remains active, owing to poly(A)-independent repression of cyclin A and B synthesis. By contrast, inactivation of MAPK alone induces M phase, even when S phase is inhibited by constitutively active Rsk. Thus, there is a divergence of separate pathways downstream of MAPK that together block the start of the embryonic mitotic cycle. One is the previously known Rsk-dependent pathway that prevents S phase, and the other is a novel pathway that is not mediated by Rsk and that leads to prevention of the first mitotic M phase through suppression of protein synthesis of M phase cyclins. Release from such a 'dual-lock' by fertilization results in the start of the embryonic cell cycle.

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Section: Control Of the Embryonic Cell Cycle Order Without Checkpointsmentioning

confidence: 99%

Start of the embryonic cell cycle is dually locked in unfertilized starfish eggs

et al. 2009

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“…Effect of RZXHomologues and Derivatives on the Polymerization of Tubulin Different concentrations of RZXhomologues (lb~3b, 4 and 5) isolated as the metabolites of Rhizopus chinensis Rh-2 and of RZXderivatives (6)(7)(8) were added to microtubule protein and their ability to inhibit tubulin polymerization was measured. IC50 values of these compoundsare shown in Table 1.…”

Section: Effect Of Rzx On Polymerized Microtubule Proteinmentioning

confidence: 99%

Studies on macrocyclic lactone antibiotics. XI. Anti-mitotic and anti-tubulin activity of new antitumor antibiotics, rhizoxin and its homologues.

et al. 1987

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The modeof action of rhizoxin (la), a new antitumor macrolide, was investigated. Rhizoxin inhibited fusion of the male and the female pronuclei in fertilized sea urchin eggs and inhibited cilia formation in the deciliated sea urchin embryos. In vitro, polymerization of tubulin isolated from porcine brains was completely inhibited at a 1 x 10~5 m concentration of rhizoxin, and tubulin which had been polymerized by incubation at 37°C for 30 minutes was depolymerized by addition of 1 x 10~5 m of the drug. Activity ofrhizoxin against tubulin polymerization was compared with those of other anti-tubulin drugs such as colchicine, vinblastine and ansamitocin P-3. The homologues of rhizoxin, lfo~3b, also inhibited polymerization of the purified microtuble protein at almost the sameextent as rhizoxin.Rhizoxin (la) is a 16 membered macrolide isolated from Rhizopus chinensis Rh-2, the pathogen of the rice seedling blight.2>3) The fungus produced also the homologues of rhizoxin, lfo~3b,4) 43) and 5n. Rhizoxin showed similar chemotherapeutic effects to those of vincristine against L1210 and P388 leukemia-bearing mice. The drug was also effective against B16 melanoma, inoculated ip or sc.5) Rhizoxin inhibited the mitosis of the tumor cells in a manner similar to that of Vinca alkaloids as revealed by morphological study and flow cytometry analysis suggesting that rhizoxin inhibits microtubule polymerization.^Wehave, therefore, studied the effects of rhizoxin on cell division in sea urchin egg to survey the mode of action of the drug and on porcine brain tubulin polymerization to confirm the results obtained using sea urchin embryos. Inhibitory activity on tubulin polymerization by rhizoxin was compared with that by colchicine, vinblastine and ansamitocin P-36) (a maytansinoid compound). Anti-tubulin activities of the rhizoxin homologues (lb~3h, 4 and 5n) and of the rhizoxin derivatives (6~8tr) were also studied ( Figs. 1 and 2). n Structural assignments of compounds 5, 6 and 8 are based on unpublished data.

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“…This is in contrast to experiments with the eggs of the starfish Asterina pectinifera: In presence of aphidicolin chromosomes condense at the time of first cleavage, becomearranged in a metaphase plate but do not "migrate" to the normally developed poles. Nevertheless cytokinesis can be completed and chromatin clumps remain at the cleavage furrow (24,27,31). This striking difference in nuclear behavior under the influence of aphidicolin is certainly worthwile to be explored further.…”

Section: Methodsmentioning

confidence: 99%

Nuclear Migration and Spindle Formation in the Fourth Cleavage of Sea Urchin Eggs under the Influence of Inhibitors.

Czihak¹,

Kojima

1992

Cell Struct. Funct.

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ABSTRACT. Mitosis of sea urchin eggs was inhibited when exposed to 3//g/ml aphidicolin from the 2-cell stage onwards. Nevertheless the nuclei migrated to the vegetal pole at the time of the fourth unequal division in control eggs. Two or four equal or unequal asters developed. Asters in proximity to the vegetal pole were always considerably smaller than those close to the center of the two blastomeres. In contrast to colchicine, cytokinesis but not migration of the nuclei in the vegetal half was prevented by treatments with 5^M cytochalasin B or D. Various mitotic figures were formed in the vegetal blastomeres of eggs treated with 0.4 mMcolchicine or 3^M griseofulvin after the third cleavage. In some eggs a centrally localized monaster with chromosomesin spherelike arrangement was formed in others a monopolar mitotic figure pushed the chromosomesin bowl-like arrangements to the most vegetal cortex. In anaphase one set of chromatids migrated to the monopole leaving the scattered sister-chromatids behind. The mechanism of migration of the nuclei and of chromosome arrangement in the metaphase plate is discussed.The fourth cleavage of sea urchin eggs is particular because in early prophase the four nuclei of the vegetal blastomeres "migrate" to the vegetal pole whereas those of the animal blastomeres remain in a central position. Like in radially cleaving eggs of molluscs the eccentric position of the nuclei at the onset of mitosis results in daughter cells of unequal size. K. Dan devoted several studies to aster-and spindle-formation in this unequal cleavage (7-1 1). T. Schroeder "describes the cytoskeletal machinery during fourth cell division" (28). D.Mazia together with several coworkers published important papers on the formation of monasters and centrosome division (20, 21) among which the one of 1986 (20) is a classic in cell biology. Recently a paper by Holy and Schatten (14) emphasizes the size difference of centrosomes in micromere formation. Whenthe asters in the four vegetal blastomeres are fully developed-that is after the "migration" of the nuclei to the cortex of the vegetal pole, governed by a cortical clock (7, 15)-we find a big aster at the center of the blastomere and a very reduced and peculiar shaped one close to the cortex of the vegetal pole.The results presented here clearly show that the "migration" of nuclei is at least in part dependent on microtubules (MTs), that MTs of artificially induced monasters press the chromosomes to the cortex of the vegetal pole and that the perfect planar array of chromosomes in the equatorial plate must be the result of proportionally growing MTsfrom opposite poles. Our results also confirm the findings of Mazia et al. (21) showing that MTsof a monaster establish contact with only one kinetochore because only one chromatid of each chromosome "migrates" to the monopole. MATERIALS AND METHODS

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Achromosomal cleavage of fertilized starfish eggs in the presence of aphidicolin

Cited by 83 publications

References 9 publications

Start of the embryonic cell cycle is dually locked in unfertilized starfish eggs

Start of the embryonic cell cycle is dually locked in unfertilized starfish eggs

Studies on macrocyclic lactone antibiotics. XI. Anti-mitotic and anti-tubulin activity of new antitumor antibiotics, rhizoxin and its homologues.

Nuclear Migration and Spindle Formation in the Fourth Cleavage of Sea Urchin Eggs under the Influence of Inhibitors.

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