Formation of the intraluminal vesicles via the invagination of the MVB membranes.

<p>Normal mouse bladder was fixed by high pressure freezing and freeze-substitution (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0099644#pone.0099644-Hudoklin2" target="_blank">[29]</a>), cut into 60-nm sections and its urothelial umbrella cells examined by transmission EM. (<b>A</b>) An umbrella cell containing many MVBs lined with uroplakin plaques. (<b>B</b>) The limiting membranes of MVB consist of uroplakin plaques with thickened, rigid-looking leaflets (arrows) interrupted by a hinge area (asterisk), and the intraluminal vesicles (ILVs) are connected with thin, irregular filaments (filled arrowheads), and amorphous materials (open arrowhead). (<b>C and D</b>) Formation of ILVs via the invagination of the limiting membrane of MVBs (open arrows). Scale bar = 1 µm (A), 0.1 µm (B), or 0.2 µm (C and D).