Uniform sheets devoid of nanoholes form in the absence of reticulons. (A and B) Overview confocal and magnified STED images of SNAP-KDEL–labeled ER network in control and CRISPR-Cas9–KO Rtn4 U2OS cells under indicated RNAi conditions. (C) Plot represents percentage of cells with indicated ER sheet phenotypes (nonuniform, detectable nanoholes; uniform, no detectable nanoholes) for indicated conditions. Error bars show standard deviation. No statistical significance test was performed.