Fusion of apposed nuclear envelopes is frequently seen at telophase during postmitotic reorganization of the nucleus, but only rarely at other times in the cell cycle. We attempted to define an experimental system for studying changes in the nuclear envelope related to the cell cycle by varying the time of pronuclear apposition in fertilized Lytechinus variegatus eggs. This approach was based on the assumption that the period from fertilization to metaphase of the first cleavage division corresponds to the period from telophase to metaphase in the generalized cell cycle. The experimental approach used was to block the movement of the pronuclei with Colcemid and then to release this block at varying times after insemination by photochemically inactivating the Colcemid. The results show that apposed pronuclear envelopes can fuse from soon after insemination until the anticipated time of prometaphase. Fusion occurred in about 3 min as scored by light microscopy and this time did not vary significantly with the time after insemination. The potential for nuclear fusion is not restricted to pronuclei alone since diploid nuclei in binucleate cells could be fused using centrifugation in solutions of Colcemid to bring the nuclei into apposition. It is suggested that the potential for nuclear fusion is not necessarily related to the cell cycle and that modification of the nuclear envelope, possibly by association with chromatin or other fibrous material restricts nuclear fusion in most multinucleated cells.
Article| July 01 1973
NUCLEAR MEMBRANE FUSION IN FERTILIZED LYTECHINUS VARIEGATUS EGGS
John F. Aronson
From the Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
Dr. Aronson's present address is the Cardiovascular-Pulmonary Division, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104.
Received: June 01 1971
Revision Received: March 26 1973
Online ISSN: 1540-8140
Print ISSN: 0021-9525
Copyright © 1973 by The Rockefeller University Press
John F. Aronson; NUCLEAR MEMBRANE FUSION IN FERTILIZED LYTECHINUS VARIEGATUS EGGS . J Cell Biol 1 July 1973; 58 (1): 126–134. doi: https://doi.org/10.1083/jcb.58.1.126
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