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Surface contractile activity associated with isolated asters in cylindrical sand dollar eggs

1985; Wiley; Volume: 235; Issue: 2 Linguagem: Inglês

10.1002/jez.1402350208

1097-010X

R. Rappaport, Barbara N. Rappaport,

Nematode management and characterization studies

Abstract The purpose of this investigation was to explore the capacity of isolated asters of the mitotic apparatus of elicit contractile activity in adjacent cell surface. When a fertilized Echinarachnius parma egg with an intact mitotic apparatus was confined in an 82‐μm‐i.d. silicone rubber capillary, the furrow developed at the midpoint between the asters. The mitotic apparatus could be broken by inserting and ejecting the egg from the capillary. The asters of a broken mitotic apparatus were usually abnormally far apart. When asters were as far as 68 μm apart, furrowing occurred; when the intervening distance was greater, there was no furrowing. When the asters were too far apart to establish a furrow between them, constrictions appeared adjacent to one of the asters. The constrictions could shift or could cut through the asters that appeared to elicit them. Cylindrical cells in 0.015 M ethyl urethane formed furrows when the mitotic apparatus was intact but formed neither furrows nor astral constrictions when the asters were far apart. Astral constrictions did not form in the presence of an active furrow. They were frequently temporary and they appeared to be slower and less acute than normal furrows. Single asters remaining after half of the amphiaster was removed had the same effect as widely separated asters. The form of the constriction was related to the position of the aster in the cylinder. When the aster was centered, the constriction resembled a furrow; but when it was near one of the poles, the adjacent surface pulled away from the capillary wall and the radius of curvature at the pole decreased. When initially distant asters were pushed together, a furrow formed between them. These results contribute to a better understanding of the interaction between the mitotic apparatus and the egg surface and the formation of the cleavage mechanism.