Fig. 4: Localization of SKSR1 expression and translocation of the protein during invasion.

a Identification of SKSR1-3HA expression in 8 egressing merozoites. SKSR1(red) is localized near the nucleus; EF1a in green; nuclei (stained with Hoechst) in blue; scale bar = 5 µm. b Ultrastructure expansion microscopy (U-ExM) showing SKSR1 in green relative to NHS ester-stained organelles (red); nuclei in blue; scale bar = 5 µm. c Dynamics of SKSR1 expression during invasion. SKSR1 is translocated from small granules to the apical region of C. parvum sporozoites during the late phase of the host cell invasion. The cartoon images to the left of IFA panels illustrate the process of sporozoite invasion. Scale bar = 5 µm. d Immunofluorescence localization of SKSR1 at the stage when sporozoites form a cup-like structure (side view) with the host cell membrane. Scale bar = 5 µm. e Immunoelectron microscopic localization of SKSR1. SKSR1 is localized at the parasite-host interface. Scale bars = 500 nm. a–e Each experiment was performed at least twice with similar results. f A model of SKSR1 secretion during Cryptosporidium invasion. The SKSR1 protein is shown in red. Source data are provided as a Source Data file.