The mitotic, micronuclear division of the heterotrichous genus Blepharisma has been studied by electron microscopy. Dividing ciliates were selected from clone-derived mass cultures and fixed for electron microscopy by exposure to the vapor of 2% osmium tetroxide; individual Blepharisma were encapsulated and sectioned. Distinctive features of the mitosis are the presence of an intact nuclear envelope during the entire process and the absence of centrioles at the polar ends of the micronuclear figures. Spindle microtubules (SMT) first appear in advance of chromosome alignment, become more numerous and precisely aligned by metaphase, lengthen greatly in anaphase, and persist through telophase. Distinct chromosomal and continuous SMT are present. At telophase, daughter nuclei are separated by a spindle elongation of more than 40 µ, and a new nuclear envelope is formed in close apposition to the chromatin mass of each daughter nucleus and excludes the great amount of spindle material formed during division. The original nuclear envelope which has remained structurally intact then becomes discontinuous and releases the newly formed nucleus into the cytoplasm. The micronuclear envelope seems to lack the conspicuous pores that are typical of nuclear envelopes. The morphology, size, formation, and function of SMT and the nature of micronuclear division are discussed.
Article| August 01 1967
FINE STRUCTURE OF DIVISION IN CILIATE PROTOZOA : I. Micronuclear Mitosis in Blepharisma
R. A. Jenkins
From the Department of Biochemistry and Biophysics, Iowa State University, Ames, Iowa 50010.
The author's present address is the Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming 82070
Received: December 10 1966
Online Issn: 1540-8140
Print Issn: 0021-9525
Copyright © 1967 by The Rockefeller University Press
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R. A. Jenkins; FINE STRUCTURE OF DIVISION IN CILIATE PROTOZOA : I. Micronuclear Mitosis in Blepharisma . J Cell Biol 1 August 1967; 34 (2): 463–481. doi: https://doi.org/10.1083/jcb.34.2.463
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