Figure 1.

BEST1 Mutations Reduce CaCC Current in Best Disease iPSC-RPE

(A) Top, image (in grayscale) of a normal fundus; bottom left, fundus image of an individual with ARB harboring compound heterozygous mutations in BEST1 (resulting in p.Arg141His; p.Ala195Val) showing a vitelliform lesion in the macula (red arrowhead) as well as small lesions outside the macula (white arrowheads); bottom right, fundus image showing a vitelliform macular lesion (red arrowhead) in an individual with adBD caused by a heterozygous p.Arg218Cys encoding mutation in BEST1.

(B) A fully functional homo-pentameric BEST1 channel is formed by assembly of WT subunits (green), allowing movement of chloride ions (yellow circles) upon binding of calcium ions (light blue circle) (based on the eukaryotic Best1 crystal structure¹⁶).

(C) Light microscopic images of normal, mutant-specific, and isogenic control iPSC-RPE used in this study. Scale bar = 50 μm (applies to all images in C).

(D) Immunocytochemical analyses of ZO-1 and BEST1 localization in iPSC-RPE cells. Scale bar = 50 μm (applies to all images in D).

(E) CaCC current density-voltage plots from WT, ARB, or adBD iPSC-RPE cells, as determined by calculating the difference in average chloride currents in the presence or absence of calcium (Figure S1). For +calcium, n = 6 cells for WT, 12 cells for Arg141His/Ala195Val ARB, 7 cells for Asn296His adBD, 5 cells for Ala146Lys adBD, 5 cells for Arg218Cys adBD, and 10 cells for Arg218Cys>WT isogenic control; for no calcium, n = 8 cells for WT, 12 cells for Arg141His/Ala195Val ARB, 8 cells for Asn296His adBD, 7 cells for Ala146Lys adBD, 8 cells for Arg218Cys adBD, and 9 cells for Arg218Cys>WT isogenic control iPSC-RPE (data combined from at least two replicates).