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First published online 9 May 2006
doi: 10.1242/jcs.02949

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A MORN-repeat protein is a dynamic component of the Toxoplasma gondii cell division apparatus

Marc-Jan Gubbels^1,*, Shipra Vaishnava², Nico Boot^1,, Jean-François Dubremetz³ and Boris Striepen^1,2,

¹ Center for Tropical and Emerging Global Diseases, University of Georgia, Paul D. Coverdell Center, Athens, Georgia 30602, USA
² Department of Cellular Biology, University of Georgia, Paul D. Coverdell Center, Athens, Georgia 30602, USA
³ UMR CNRS 5539, Université de Montpellier 2, Montpellier, 34095, France

Author for correspondence (e-mail: striepen{at}cb.uga.edu)

Accepted 20 February 2006

Apicomplexan parasites divide and replicate through a complex process of internal budding. Daughter cells are preformed within the mother on a cytoskeletal scaffold, endowed with a set of organelles whereby in the final stages the mother disintegrates and is recycled in the emerging daughters. How the cytoskeleton and the various endomembrane systems interact in this dynamic process remains poorly understood at the molecular level. Through a random YFP fusion screen we have identified two Toxoplasma gondii proteins carrying multiple membrane occupation and recognition nexus (MORN) motifs. MORN1 is highly conserved among apicomplexans. MORN1 specifically localizes to ring structures at the apical and posterior end of the inner membrane complex and to the centrocone, a specialized nuclear structure that organizes the mitotic spindle. Time-lapse imaging of tagged MORN1 revealed that these structures are highly dynamic and appear to play a role in nuclear division and daughter cell budding. Overexpression of MORN1 resulted in severe but specific defects in nuclear segregation and daughter cell formation. We hypothesize that MORN1 functions as a linker protein between certain membrane regions and the parasite's cytoskeleton. Our initial biochemical analysis is consistent with this model. Whereas recombinant MORN1 produced in bacteria is soluble, in the parasite MORN1 was associated with the cytoskeleton after detergent extraction.

Key words: Toxoplasma, Apicomplexa, Inner membrane complex, MORN, Cell division, Parasite

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