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J Cell Sci. 2013 May 15;126(Pt 10):2246-55. doi: 10.1242/jcs.121632. Epub 2013 Mar 22.

The Giardia cell cycle progresses independently of the anaphase-promoting complex.

Author information

1
Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA. stephane.gourguechon@berkeley.edu

Abstract

Most cell cycle regulation research has been conducted in model organisms representing a very small part of the eukaryotic domain. The highly divergent human pathogen Giardia intestinalis is ideal for studying the conservation of eukaryotic pathways. Although Giardia has many cell cycle regulatory components, its genome lacks all anaphase-promoting complex (APC) components. In the present study, we show that a single mitotic cyclin in Giardia is essential for progression into mitosis. Strikingly, Giardia cyclin B lacks the conserved N-terminal motif required for timely degradation mediated by the APC and ubiquitin conjugation. Expression of Giardia cyclin B in fission yeast is toxic, leading to a prophase arrest, and this toxicity is suppressed by the addition of a fission yeast degradation motif. Cyclin B is degraded during mitosis in Giardia cells, but this degradation appears to be independent of the ubiquitination pathway. Other putative APC substrates, aurora and polo-like kinases, also show no evidence of ubiquitination. This is the first example of mitosis not regulated by the APC and might reflect an evolutionary ancient form of cell cycle regulation.

KEYWORDS:

APC; Anaphase-promoting complex; Calyculin A; Cyclin B; Giardia; Mitosis; Staurosporine

PMID:
23525017
PMCID:
PMC3672939
DOI:
10.1242/jcs.121632
[Indexed for MEDLINE]
Free PMC Article
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