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. 2022 Mar 9;96(5):e01813-21. doi: 10.1128/jvi.01813-21

FIG 5.

FIG 5

SM-cholesterol complex domains are required for the constriction of the CCS bound by IAV. (A) Representative transmission electron micrographs of the CCSs. (Left) No IAV addition; (right) with the IAV virion. (B and C) Fractions of the CCSs at stages 1, 2, and 3 to 4 before and after cholesterol depletion using MβCD. (B) No IAV addition; (C) CCSs with an IAV virion. The numbers of CCSs observed were 166 and 134 (no IAV addition) and 66 and 57 (with an IAV virion) before and after cholesterol depletion, respectively. Cholesterol depletion (accessible and/or SM-sequestered cholesterol) slowed the invagination of CCSs without any IAV virion, inducing an increase of the CCSs in stage 1 (plate type), with a concomitant decrease of the CCSs in stages 3 and 4 (bowl and vesicle types). With the binding of an IAV virion, even under cholesterol-depleted conditions, the transition from stage 1 to stage 2 occurred at a normal rate (no increase of the CCSs in stage 1). However, the cholesterol domain was required for the transition from stage 2 to stage 3.