Focused CRISPR-Cas9 screen identifies SNORD42A as a growth regulator for leukemia cells. (A) Experimental design of the CRISPR-Cas9 snoRNA screen. Leukemic cells were infected with the designed CRISPR-Cas9 snoRNA library. Samples were taken at day 1, 5, and 9. The relative frequency of each gRNA was determined by deep sequencing. (B) Number of raw counts for each sgRNA included in the screen. More than 99% of all sgRNAs were detected at day 1 in the analyzed cells. (C) Fold changes of all sgRNAs from day 9 to day 1 as mean from all experiments. The blue bar shows the ratio of SNORD42A gRNA2 (log2 fold change = −0.83). Positive controls are sgRNAs targeting essential genes (c-MYC, EIF4A1, and RUNX1). (D) Clustering of snoRNAs (n = 52) that had a significant (P < .05) negative MAGeCK score in at least on condition (day 5 to day 1 or day 9 to day 1) in 1 cell line. For these snoRNAs, the heatmap shows the negative MAGeCK score from day 5 to day 1 and from day 9 to day 1 for each cell line. *P < .05 for SNORD42A. (E) Changes of SNORD42A gRNA2 as mean of 2 replicates from day 5 to day 1 and from day 9 to day 1 in all cell lines.