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Reconciling an archaeal origin of eukaryotes with engulfment: a biologically plausible update of the Eocyte hypothesis
Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
2011 (English)In: Research in Microbiology, ISSN 0923-2508, E-ISSN 1769-7123, Vol. 162, no 1, 71-76 p.Article in journal (Refereed) Published
Abstract [en]

An archaeal origin of eukaryotes is often equated with the engulfment of the bacterial ancestor of mitochondria by an archaeon. Such an event is problematic in that it is not supported by archaeal cell biology. We show that placing phylogenetic results within a stem-and-crown framework eliminates such incompatibilities, and that an archaeal origin for eukaryotes (as suggested from recent phylogenies) can be uncontroversially reconciled with phagocytosis as the mechanism for engulfment of the mitochondrial ancestor. This is significant because it eliminates a perceived problem with eukaryote origins: that an archaeal origin of eukaryotes (as under the Eocyte hypothesis) cannot be reconciled with existing cell biological mechanisms through which bacteria may take up residence inside eukaryote cells.

Place, publisher, year, edition, pages
2011. Vol. 162, no 1, 71-76 p.
Keyword [en]
Stem group, Crown group, Eocyte hypothesis, Phagocytosis, Eukaryotes, Archaea
National Category
Biological Sciences
Research subject
Molecular Biology
Identifiers
URN: urn:nbn:se:su:diva-68644DOI: 10.1016/j.resmic.2010.10.002ISI: 000289500000008OAI: oai:DiVA.org:su-68644DiVA: diva2:473689
Note

2

Available from: 2012-01-07 Created: 2012-01-04 Last updated: 2017-12-08Bibliographically approved
In thesis
1. The evolution of the nuclear envelope
Open this publication in new window or tab >>The evolution of the nuclear envelope
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The nucleus is one of the defining features of eukaryotes and the question of its origin is intimately linked to the evolution of the eukaryotic cell. It is delimited by a double lipid bilayer called the nuclear envelope, which separates the nuclear interior from the cytoplasm. The inner and outer membranes of the nucleus are continuous with one another creating a single folded envelope, interrupted by nuclear pore complexes (NPCs), which enable transport of proteins and RNA between nucleoplasm and cytoplasm.

A combination of proteomic and bioinformatic analyses has shown that numerous Nups are conserved between yeast and vertebrates. As this only describes a subset of eukaryotic diversity, comparative genomic analyses were used to establish the extent to which the NPC is conserved across the eukaryotic tree. NPCs have been suggested to share a common origin with vesicle coat proteins of the endomembrane system. An additional goal of this work was therefore to establish the distribution of three complexes involved in vesicle transport between organelles of the secretory pathway, called COPI, COPII and Clathrin.

Using profile hidden Markov models in combination with BLAST resulted in identification of nucleoporins and coat protein homologs across all five eukaryotic supergroups for which sequence data is available, indicating both were already present in the Last Eukaryotic Common Ancestor (LECA).Nup homologs were shown to be definitively absent from vestigial nucleomorph nuclei, resultant from secondary endosymbioses, suggesting that Nup genes have either been relocated to the host nuclear genome or that the same set of Nups are used for constructing both the NPC of the main nucleus and nucleomorph.´

We also tested the proposal that transmembrane Nups in vertebrates and yeasts may account for their variant forms of mitosis (‘open’ in vertebrates, ‘closed’ among yeasts). Consistent with this suggestion, the distribution of fungal Pom34 fits a scenario wherein it was integral to the evolution of 'closed’ mitosis in ascomycetes.A unique arrangement for the chromosomes occurs during early meiosis, where the telomeres cluster at the nuclear envelope, forming a distinct ‘bouquet’ arrangement. This forms prior to homolog pairing and recombination in meiosis I. Hypotheses concerning the antiquity of the bouquet were tested by examining the extent of conservation of proteins involved in this stage of meiosis. Distribution appeared patchy, so its presence in LECA could not be unequivocally established and is discussed together with a model aimed at explaining the functional role of the bouquet.

Place, publisher, year, edition, pages
Stockholm: Department of Molecular Biology and Functional Genomics, Stockholm University, 2010. 58 p.
Keyword
Nuclear pore complex, bouquet, meiosis, nucleus, eukaryote evolution, nucleoporin, tree of life, stem group, recombination
National Category
Biochemistry and Molecular Biology
Research subject
Molecular Biology
Identifiers
urn:nbn:se:su:diva-42259 (URN)978-91-7155-956-2 (ISBN)
Public defence
2010-10-04, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 3: Manuscript. Paper 4: manuscript.Available from: 2010-09-12 Created: 2010-08-20 Last updated: 2012-05-24Bibliographically approved

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