Figure 8

MLL1 is required for horizontal cell integrity. Retinal cross-sections of CreNeg and Mll1KO mice at P0 (A,B), P7 (D,E) and P14 (G,H), immunostained for OC1 (green) to mark horizontal cells (arrowheads). Quantification of OC1 + cells per retina cross-section at P0 (C), P7 (F) and P14 (I), presented as mean OC1 + cells per cross-section + SEM. *p < 0.05, n.s. = not significant by two-way ANOVA with Tukey’s multiple comparisons (n = 3). To further assess horizontal cell distribution and connectivity in 1MO retinas, immunostaining was performed on retinal cross-sections (J,K) for Calbindin (red), which labels cell bodies of HC and AC, and Neurofilament medium chain (green), which labels their axons. (J,K) Retinal cross-sections show the clear spatial distribution of HC (arrowheads) and AC (white arrows). Flat mounts of 1MO CreNeg (L) and Mll1KO retinas (M), imaged with confocal microscopy at the level of the OPL and outer INL revealed defects in the HC mosaic and axon distribution network, as well as interrupted neurofilaments (arrows) and axon varicosities (arrowheads) in Mll1KO retinas. Antibody information is given in Supplementary Table S2.