Functional and non-functional spindle formation affecting mitosis and cytokinesis in Fucus distichus zygotes: the role of the centrosome

摘要

Functional (with centrioles) and non-functional (without centrioles) mitotic spindle formation was studied in Fucus distichus zygotes. In normally fertilized zygotes, a pair of centrioles derived from sperm existed at both mitotic poles. Both centrin and gamma-tubulin were associated with centrioles. In multipolar spindles of fertilized multinucleate eggs, mitotic poles with centrioles were stained with an anti-gamma-tubulin antibody, but the other poles were not, and cytokinesis proceeded abnormally. When karyogamy was blocked with colchicine, centrioles remained around the sperm nucleus. A monastral spindle or a bipolar, barrel-shaped spindle was formed on the egg nucleus; however, there were no centrioles at these mitotic poles. When cytoplasmic fragments containing only an egg or a sperm nucleus were separately prepared and cultured, the egg nucleus appeared to enter, but did not complete, mitosis. In cytoplasm containing only a sperm nucleus, mitosis and cytokinesis did not occur. We concluded that the egg nucleus has the potential to form a non-functional spindle without the sperm centrioles. However, this acentrosomal spindle was non-functional; mitosis remained at the stage of chromosome condensation and did not proceed to cytokinesis. Even though some cells proceeded to cytokinesis, they showed abnormal chromosome condensation.