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. 2021 Dec 30;62(15):32. doi: 10.1167/iovs.62.15.32

Figure 1.

Figure 1.

ICPSER in retinal pigmented epithelial cells of Rhesus Monkey. (A) Two adjacent retinal pigmented epithelial cells (RPE) are provided with ICPSER (arrows) at the corner of the lateral (arrowheads) and basal cell membranes. Monkey R10026. BM = Bruch's membrane. Magnification bar, 350 nm. (B) ICPSER (arrows) at higher magnification. The ICPSER shows a periodic array due to the checkerboard pattern of larger tubular structures surrounded by two concentric membranes and very small tubules (arrowheads) outlined by a single membrane. Larger and smaller tubules are apparently joined by straight filament-like elements. Monkey R10026. Magnification bar, 120 nm. (C) Electron tomography of an ICPSER unveils its complex nature. Thin axial slices (0.6 nm thick) show that membrane profiles follow a regular pattern realized by the alternation of larger C-shaped and smaller rounded tubules. This is particularly evident on the left where the section has a more favorable orientation. The distance between adjacent C-shaped tubules or between a C-shaped tubule and a rounded tubule is remarkably constant (8.5 nm). Monkey R10019. Magnification bar, 120 nm. (D) To generate a 3D-model of the ICPSER, membrane profiles have been retraced with different colors according to their continuity through the entire series of axial slices. Four major compartments, red, green, yellow and purple, can be identified. A fifth minor compartment (blue) can also be seen. Monkey R10019. Magnification bar, 120 nm. (E) A 3D rendering of the ICPSER. The model has been rotated on the z-axis to align compartments along the x- and y-axes. Four vertical rows (highlighted with numbered squared brackets) of different elements aligned along the y-axis can be appreciated as well as the alternation of C-shaped and rounded tubules (particularly as far as rows #1 and #2 are concerned). Periodicity in the model includes the regular sequence of the four major compartments that, however, follow inverted orders when comparing adjacent rows. A fifth minor compartment in blue (arrow) can also be seen as a single tubule traversing the ICPSER. Monkey R10019. Magnification bar, 120 nm. (F) A 3D rendering of the ICPSER. The model is the same shown in E though rotated by 40° on the x-axis. Magnification bar, 120 nm.