title: The apical complex provides a regulated gateway for secretion of invasion factors in Toxoplasma.
abstract: The apical complex is the definitive cell structure of phylum Apicomplexa, and is the focus of the events of host cell penetration and the establishment of intracellular parasitism. Despite the importance of this structure, its molecular composition is relatively poorly known and few studies have experimentally tested its functions. We have characterized a novel Toxoplasma gondii protein, RNG2, that is located at the apical polar ring--the common structural element of apical complexes. During cell division, RNG2 is first recruited to centrosomes immediately after their duplication, confirming that assembly of the new apical complex commences as one of the earliest events of cell replication. RNG2 subsequently forms a ring, with the carboxy- and amino-termini anchored to the apical polar ring and mobile conoid, respectively, linking these two structures. Super-resolution microscopy resolves these two termini, and reveals that RNG2 orientation flips during invasion when the conoid is extruded. Inducible knockdown of RNG2 strongly inhibits host cell invasion. Consistent with this, secretion of micronemes is prevented in the absence of RNG2. This block, however, can be fully or partially overcome by exogenous stimulation of calcium or cGMP signaling pathways, respectively, implicating the apical complex directly in these signaling events. RNG2 demonstrates for the first time a role for the apical complex in controlling secretion of invasion factors in this important group of parasites.
authors.affiliation: School of Botany, The University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Katris
authors.affiliation: Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia.
authors.forename: Giel G
authors.initials: GG
authors.lastname: van Dooren
authors.affiliation: Biological Optical Microscopy Platform, The University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: McMillan
authors.affiliation: Advanced Microscopy Facility, The University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Eric
authors.initials: E
authors.lastname: Hanssen
authors.affiliation: Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, and Australian Research Council Centre of Excellence for Coherent X-ray Science, The University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Leann
authors.initials: L
authors.lastname: Tilley
authors.affiliation: School of Botany, The University of Melbourne, Parkville, Victoria, Australia; Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Ross F
authors.initials: RF
authors.lastname: Waller
mesh_terms: D002460:Cell Line; D006152:Cyclic GMP / Q000235:genetics / Q000378:metabolism; D055785:Gene Knockdown Techniques; D006801:Humans; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014122:Toxoplasma / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D014123:Toxoplasmosis / Q000235:genetics / Q000378:metabolism*
chemical_list: D015800:Protozoan Proteins; D006152:Cyclic GMP
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