Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Cell Nucleus Division”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6Linked to original sources
PubMed1963

A correlated light and electron microscope study of the nucleolar material during mitosis in Vicia faba.

Root meristematic cells of Vicia faba were examined, with both light and electron microscopes, in order to study the behaviour of the nucleolar material during the mitotic process. Under light microscopy, the preprophase nucleolus is seen to consist of a densely stained material in which are embedded several unstained vacuole-like structures of varying size. The electron microscope reveals that the dense nucleolar material is formed of two structurally distinct components, each segregated into irregularly shaped zones blending with one another. One of these components is represented by 150 A granules which, in places, are arranged into thread-like structures approximately 0.1 micro in diameter; the other component apparently consists of fibrils 60 to 100 A in diameter. The large and medium sized intranucleolar vacuoles contain loosely scattered granules and fibrils similar to those just described. The granular and fibrillar components of the denser portion of the nucleolus persist as such during prophase and disperse throughout the nuclear cavity at the time of nucleolar disintegration. After nuclear membrane breakdown, these granules and fibrils, as well as those of the nucleoplasm, mix freely with similar elements already present within the forming spindle. No evidence has been obtained that, during or after nucleolar disintegration, the structural components of the nucleolus become associated as such with the chromosomes to form an external or internal matrix. Our observations suggest the existence, of a matrix substance within late prophase, metaphase, and anaphase chromosomes, the fine structure of which bears strong resemblance to that of their constituent coiled chromonemata. Data are presented, moreover, that indicate that part of this matrix substance, presumably formed at some time during prophase, is released from the chromosomes during their anaphasic movement. A number of observations indicate that the main bulk of the next nucleolus is derived from a prenucleolar fibrillogranular material, arranged into thread-like structures some 0.1 micro in diameter, which collect in the interchromosomal spaces during early and midtelophase. Finally, our data would seem to favour the view that most of this prenucleolar material results from a resumption of the synthetic activity of the early and midtelophase chromosomes rather than from a mere shedding of a preexisting matrix substance.

Anaphase↗
PubMed1964

HISTONE PROTEIN TRANSITION IN DROSOPHILA MELANOGASTER. II. CHANGES DURING EARLY EMBRYONIC DEVELOPMENT.

Employing cytochemical methods it was found that during the early embryonic development of Drosophila melanogaster the nuclei contain in sequence two kinds of chromosomal proteins. The cleavage nuclei (as also the pronuclei), until shortly before the blastoderm stage, contain an atypical (or juvenile) histone, stainable with bromophenol blue but not with alkaline fast green. The typical fast green-positive histone appears at the close of the period of the synchronized cleavage mitoses, just before blastulation, when nucleoli are first produced. The amount of DNA of the cleavage nuclei, as determined cytophotometrically, is nearly constant; therefore, the DNA moiety of the nucleohistone complex seems to remain unaffected by the protein shift during embryonic development. The implications of the protein shift in relation to the histone control of gene expression are discussed.

Animals↗