Fig 1.

TgSAS6 and TgSAS6L localize to distinct regions in Toxoplasma tachyzoites. (A) The Toxoplasma homolog of SAS6 (green) localizes to centrioles along with the centriole marker centrin (red). The overlap between these proteins is not complete, which likely reflects distinct localization within centrioles; while centrin is typically located throughout the centriole, SAS-6 is a marker of the proximal end of centrioles. (B) TgSAS6L (red, anti-SAS6L antiserum) is found at the apex of Toxoplasma tachyzoites and does not colocalize with SAS-6 in the centrioles (green, YFP tag). (C) Ionomycin triggers conoid extrusion in most extracellular parasites. In these cells, SAS6L-mCherry labeling (red) is above the APR (RNG1-YFP, green). (D) When the conoid is retracted, TgSAS6L and RNG1-YFP partially colocalize (the preconoidal region is smaller than the APR). (E) Extraction of extracellular tachyzoites with DOC frees the subpellicular microtubules and conoid (blue) and APR (RNG1-YFP, green) from other cellular material. TgSAS6L is located at the apical end of the conoid, and RNG1-YFP is beneath the extended conoid at the APR. The tubulin channel alone permits identification of the conoid (arrows) above the subpellicular microtubules. (F) Immunogold labeling indicates that SAS6L-YFP localizes to the extreme apical region of Toxoplasma tachyzoites, above the conoid in both longitudinal (arrows, top) and transverse (arrows, bottom) sections of the apical region. Scale bars, 2 μm (A to E) or 250 nm (F).