Detection of microtubule-forming capacity of the centrosome reveaed by its transplantation at meiosis and mitosis

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In order to investigate differences among the first and second maturation divisions and the first cleavage, we transplanted a centrosome at each division into maturating oocytes or zygotes of the starfish, A.pectinifera. In the zaygtes, the cenrosome deried from every divisions formed an aster, which induced cytokinesis, and eventually the reciient zygote divided nto three blastomeres after the first cleavage. The centrosome derved from any division also formed an aster in maturing ocytes. However, the plar body extrusion always occurred normally ; namely, an aster additionaly formed in the recipient oocyte never induced cytokinesis. Stabilizing the mitotic aster with hexylene glycol (HG) treatment demonstrated clearly that the size of the aster at maturation was smaller than that at the first clevage Asters reduced in size at the first cleavage with clcemid treatment failed in nducing cytokinesis. Therefore, it is concluded that the centrosome has no functinal differencein aster formatin among maturation and cleavage, and, however, that the size of the resultant aster determines whether or not cell division is induced.When maturing oocytes were treated with HG at about 1%, the resultant first polar body (PB1) increased in size and sometimes divided. The division rate clearly increased when their size became larger, and the rate of enlarged PB1 whose diameter was 1.6 times larger than that of normal PB1 reached 50%. Staining microtubules immunofluorescently revealed that there was the itotic apparatus similar to that at the secnd meiosis in enlarged PB1s. When PB1 was transplanted, additional asters were induced in the recipient zygote, and the number of asters increased frm ne to two with time after its extrusion. These results indicate that the ceentrosome in PB1 may duplicate, but does not organize the mitotic appaatus, which appeared in enlarged PB1.