title: The toxoplasma-host cell junction is anchored to the cell cortex to sustain parasite invasive force.
abstract: BACKGROUND
  The public health threats imposed by toxoplasmosis worldwide and by malaria in sub-Saharan countries are directly associated with the capacity of their related causative agents Toxoplasma and Plasmodium, respectively, to colonize and expand inside host cells. Therefore, deciphering how these two Apicomplexan protozoan parasites access their host cells has been highlighted as a priority research with the perspective of designing anti-invasive molecules to prevent diseases. Central to the mechanism of invasion for both genera is mechanical force, which is thought to be applied by the parasite at the interface between the two cells following assembly of a unique cell-cell junction but this model lacks direct evidence and has been challenged by recent genetic studies. In this work, using parasites expressing the fluorescent core component of this junction, we analyze characteristic features of the kinematics of penetration of more than 1,000 invasion events.
  
  
  RESULTS
  The majority of invasion events occur with a typical forward rotational progression of the parasite through a static junction into an invaginating host cell plasma membrane. However, if parasites encounter resistance and if the junction is not strongly anchored to the host cell cortex, as when parasites do not secrete the toxofilin protein and, therefore, are unable to locally remodel the cortical actin cytoskeleton, the junction travels retrogradely with the host cell membrane along the parasite surface allowing the formation of a functional vacuole. Kinetic measurements of the invasive trajectories strongly support a similar parasite driven force in both static and capped junctions, both of which lead to successful invasion. However, about 20% of toxofilin mutants fail to enter and eventually disengage from the host cell membrane while the secreted RhOptry Neck (RON2) molecules are posteriorally capped before being cleaved and released in the medium. By contrast in cells characterized by low cortex tension and high cortical actin dynamics junction capping and entry failure are drastically reduced.
  
  
  CONCLUSIONS
  This kinematic analysis newly highlights that to invade cells parasites need to engage their motor with the junction molecular complex where force is efficiently applied only upon proper anchorage to the host cell membrane and cortex.
authors.affiliation: Department of Cell Biology of Host-Pathogen Interactions, Inserm U1016, Institut Cochin, 22 Rue Méchain, 75014, Paris, France. bichetmarion@gmail.com.|Department of Cell Biology of Host-Pathogen Interactions, Cnrs UMR8104, 22 Rue Méchain, 75014, Paris, France. bichetmarion@gmail.com.|Department of Cell Biology of Host-Pathogen Interactions, Université Paris Descartes, Sorbonne Paris Cité, 22 Rue Méchain, 75014, Paris, France. bichetmarion@gmail.com.
authors.forename: Marion
authors.initials: M
authors.lastname: Bichet
authors.affiliation: Department of Cell Biology of Host-Pathogen Interactions, Inserm U1016, Institut Cochin, 22 Rue Méchain, 75014, Paris, France. candie.joly@hotmail.fr.|Department of Cell Biology of Host-Pathogen Interactions, Cnrs UMR8104, 22 Rue Méchain, 75014, Paris, France. candie.joly@hotmail.fr.|Department of Cell Biology of Host-Pathogen Interactions, Université Paris Descartes, Sorbonne Paris Cité, 22 Rue Méchain, 75014, Paris, France. candie.joly@hotmail.fr.
authors.forename: Candie
authors.initials: C
authors.lastname: Joly
authors.affiliation: Department of Cell Biology of Host-Pathogen Interactions, Inserm U1016, Institut Cochin, 22 Rue Méchain, 75014, Paris, France. ahadjhenni@gmail.com.|Department of Cell Biology of Host-Pathogen Interactions, Cnrs UMR8104, 22 Rue Méchain, 75014, Paris, France. ahadjhenni@gmail.com.|Department of Cell Biology of Host-Pathogen Interactions, Université Paris Descartes, Sorbonne Paris Cité, 22 Rue Méchain, 75014, Paris, France. ahadjhenni@gmail.com.
authors.forename: Ahmed Hadj
authors.initials: AH
authors.lastname: Henni
authors.affiliation: Department of Cell Biology of Host-Pathogen Interactions, Inserm U1016, Institut Cochin, 22 Rue Méchain, 75014, Paris, France. thomas.guilbert@inserm.fr.|Department of Cell Biology of Host-Pathogen Interactions, Cnrs UMR8104, 22 Rue Méchain, 75014, Paris, France. thomas.guilbert@inserm.fr.|Department of Cell Biology of Host-Pathogen Interactions, Université Paris Descartes, Sorbonne Paris Cité, 22 Rue Méchain, 75014, Paris, France. thomas.guilbert@inserm.fr.
authors.forename: Thomas
authors.initials: T
authors.lastname: Guilbert
authors.affiliation: Department of Cell Biology of Host-Pathogen Interactions, Inserm U1016, Institut Cochin, 22 Rue Méchain, 75014, Paris, France. marie.xemard@u-psud.fr.|Department of Cell Biology of Host-Pathogen Interactions, Cnrs UMR8104, 22 Rue Méchain, 75014, Paris, France. marie.xemard@u-psud.fr.|Department of Cell Biology of Host-Pathogen Interactions, Université Paris Descartes, Sorbonne Paris Cité, 22 Rue Méchain, 75014, Paris, France. marie.xemard@u-psud.fr.
authors.forename: Marie
authors.initials: M
authors.lastname: Xémard
authors.affiliation: Department of Cell Biology of Host-Pathogen Interactions, Inserm U1016, Institut Cochin, 22 Rue Méchain, 75014, Paris, France. vtafani@Pive.fr.|Department of Cell Biology of Host-Pathogen Interactions, Cnrs UMR8104, 22 Rue Méchain, 75014, Paris, France. vtafani@Pive.fr.|Department of Cell Biology of Host-Pathogen Interactions, Université Paris Descartes, Sorbonne Paris Cité, 22 Rue Méchain, 75014, Paris, France. vtafani@Pive.fr.
authors.forename: Vincent
authors.initials: V
authors.lastname: Tafani
authors.affiliation: Department of Cell Biology of Host-Pathogen Interactions, Inserm U1016, Institut Cochin, 22 Rue Méchain, 75014, Paris, France. vanessalagal@gmail.com.|Department of Cell Biology of Host-Pathogen Interactions, Cnrs UMR8104, 22 Rue Méchain, 75014, Paris, France. vanessalagal@gmail.com.|Department of Cell Biology of Host-Pathogen Interactions, Université Paris Descartes, Sorbonne Paris Cité, 22 Rue Méchain, 75014, Paris, France. vanessalagal@gmail.com.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Lagal
authors.affiliation: Department of Cell and Developmental Biology, London Centre for Nanotechnology, University College London, 17-19 Gordon Street, WC1H 0AH, London, UK. g.charras@ucl.ac.uk.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Charras
authors.affiliation: Department of Cell Biology of Host-Pathogen Interactions, Inserm U1016, Institut Cochin, 22 Rue Méchain, 75014, Paris, France. isabelle.tardieux@inserm.fr.|Department of Cell Biology of Host-Pathogen Interactions, Cnrs UMR8104, 22 Rue Méchain, 75014, Paris, France. isabelle.tardieux@inserm.fr.|Department of Cell Biology of Host-Pathogen Interactions, Université Paris Descartes, Sorbonne Paris Cité, 22 Rue Méchain, 75014, Paris, France. isabelle.tardieux@inserm.fr.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Tardieux
mesh_terms: D051344:Actin Capping Proteins / Q000235:genetics / Q000378:metabolism; D000199:Actins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured / Q000469:parasitology; D006790:Host-Parasite Interactions / Q000235:genetics / Q000502:physiology*; D006801:Humans; D007365:Intercellular Junctions / Q000469:parasitology*; D008164:Luminescent Proteins / Q000235:genetics; D008954:Models, Biological; D010961:Plasmodium / Q000502:physiology*; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D014122:Toxoplasma / Q000502:physiology*
chemical_list: D051344:Actin Capping Proteins; D000199:Actins; D008164:Luminescent Proteins; D015800:Protozoan Proteins; C559757:rhoptry neck protein 2, Toxoplasma gondii; C406004:toxofilin protein, Toxoplasma gondii