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The structure of the mitotic spindle and nucleolus during mitosis in the amebo-flagellate naegleria

Walsh, CJ (2012) The structure of the mitotic spindle and nucleolus during mitosis in the amebo-flagellate naegleria. PLoS ONE, 7 (4).

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Mitosis in the amebo-flagellate Naegleria pringsheimi is acentrosomal and closed (the nuclear membrane does not break down). The large central nucleolus, which occupies about 20% of the nuclear volume, persists throughout the cell cycle. At mitosis, the nucleolus divides and moves to the poles in association with the chromosomes. The structure of the mitotic spindle and its relationship to the nucleolus are unknown. To identify the origin and structure of the mitotic spindle, its relationship to the nucleolus and to further understand the influence of persistent nucleoli on cellular division in acentriolar organisms like Naegleria, three-dimensional reconstructions of the mitotic spindle and nucleolus were carried out using confocal microscopy. Monoclonal antibodies against three different nucleolar regions and α-tubulin were used to image the nucleolus and mitotic spindle. Microtubules were restricted to the nucleolus beginning with the earliest prophase spindle microtubules. Early spindle microtubules were seen as short rods on the surface of the nucleolus. Elongation of the spindle microtubules resulted in a rough cage of microtubules surrounding the nucleolus. At metaphase, the mitotic spindle formed a broad band completely embedded within the nucleolus. The nucleolus separated into two discreet masses connected by a dense band of microtubules as the spindle elongated. At telophase, the distal ends of the mitotic spindle were still completely embedded within the daughter nucleoli. Pixel by pixel comparison of tubulin and nucleolar protein fluorescence showed 70% or more of tubulin co-localized with nucleolar proteins by early prophase. These observations suggest a model in which specific nucleolar binding sites for microtubules allow mitotic spindle formation and attachment. The fact that a significant mass of nucleolar material precedes the chromosomes as the mitotic spindle elongates suggests that spindle elongation drives nucleolar division. © 2012 Charles J. Walsh.


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Item Type: Article
Status: Published
CreatorsEmailPitt UsernameORCID
Walsh, CJcwalsh@pitt.eduCWALSH
ContributionContributors NameEmailPitt UsernameORCID
Date: 6 April 2012
Date Type: Publication
Journal or Publication Title: PLoS ONE
Volume: 7
Number: 4
DOI or Unique Handle: 10.1371/journal.pone.0034763
Schools and Programs: Dietrich School of Arts and Sciences > Biological Sciences
Refereed: Yes
MeSH Headings: Cell Nucleolus--physiology; Cell Nucleolus--ultrastructure; Chromosomes--ultrastructure; Metaphase--physiology; Microscopy, Confocal; Microtubules--physiology; Microtubules--ultrastructure; Mitosis--physiology; Mitotic Spindle Apparatus--physiology; Mitotic Spindle Apparatus--ultrastructure; Naegleria--physiology; Naegleria--ultrastructure; Nuclear Envelope--physiology; Nuclear Envelope--ultrastructure; Nuclear Proteins--ultrastructure; Prophase--physiology; Telophase--physiology; Tubulin--ultrastructure
Other ID: NLM PMC3321029
PubMed Central ID: PMC3321029
PubMed ID: 22493714
Date Deposited: 24 Sep 2012 20:04
Last Modified: 02 Feb 2019 14:55


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