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Fig. 8. A scheme of some early events during C. caviae entry. Interaction of a bacterium (grey circle) with the host cell plasma membrane induces the clustering of cholesterol-rich membrane domains (orange line), a phenomenon that might participate in initiating intracellular signalling. Signalling for entry might also be mediated by putative effector molecule(s) secreted by a type III mechanism. The small GTPases Cdc42 and Rac, which control proper actin polymerization, are rapidly activated. Abundant protein phosphorylation is detected and phosphorylated proteins (orange shapes) accumulate at the entry sites where they take part in the signalling cascade. In particular, several phosphorylated proteins can interact with the PI 3-kinase (blue), whose activity is required for C. caviae entry. Activation of Cdc42 and Rac is transient and is followed by the depolymerization of actin filaments, associated with a decrease in the accumulation of phosphorylated proteins around internalized bacteria. Although bacteria-associated actin patches have disappeared 45 minutes p.i., general remodelling of the cytoskeleton can be observed for longer times after infection.
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