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Journal of Cell Science, Vol 102, 475-485, Copyright © 1992 by Company of Biologists

Submitted on February 6, 1992
Accepted on March 19, 1992

Nucleolus behaviour during the cell cycle of a primitive dinoflagellate eukaryote, Prorocentrum micans Ehr., seen by light microscopy and electron microscopy

MARIE-ODILE SOYER-GOBILLARD 1 and MARIE-LINE GERAUD 1

1 Départemenl de Biologie Cellulaire, Observatoire Océanologique de Banyuls, Université P. et M. Curie, Laboraloire Arago, URA CNRS 117, 66650 Banyuls-sur-mer, France

To whom correspondence should be addressed

Light-microscopy observation of the dinoflagellate Prorocentrum micans after silver-staining of the argyrophilic proteins of the nucleolar organizing region (Ag-NOR staining) showed the presence of nucleolar material throughout the vegetative cell cycle, and in particular during all the mitotic stages. This contrasts with the case in most higher eukaryotes, in which nucleoli disappear at the end of prophase and are reconstituted in daughter cells during telophase.

Electron-microscope (EM) observations after conventional or fast-freeze fixation revealed that during interphase several functional nucleoli with three compartments (NORs, the fibrillogranular and the preribosomal granular compartments) are present in a nucleus in which the envelope is persistent and the chromosomes are always compact. During early prophase, when chromosomes are beginning to split, the nucleoli remain functional, whereas in late prophase they contain only a NOR and the granular component, and the chromosomes are surrounded by many protein masses. In early telophase, the nucleolar material coating the chromosomes migrates along with the chromosomes. Nucleologenesis occurs through the formation of prenucleolar bodies around lateral or telomeric nucleofilaments extruding from the chromosomes. Several chromosomes can contribute to the formation of one nucleolus. The behaviour of these ‘persistent nucleoli’ in a closed-nucleus model such as that of the dinoflagellates is discussed with regard to the higher eukaryotes.

Key words: nucleolus, nuclear cycle, mitosis, Prorocentrum micans, dinofiagellate

Submitted on February 6, 1992
Accepted on March 19, 1992




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© The Company of Biologists Ltd 1992