Initial characterization of WDR5B reveals a role in the proliferation of retinal pigment epithelial cells

The chromatin-associated protein WDR5 has been widely studied due to its role in histone modification and its potential as a pharmacological target for the treatment of cancer. In humans, the protein with highest sequence homology to WDR5 is encoded by the retrogene WDR5B, which remains unexplored. Here, we used CRISPR-Cas9 genome editing to generate WDR5B knockout and WDR5B-FLAG knock-in cell lines for further characterization. In contrast to WDR5, WDR5B exhibits low expression in pluripotent cells and is upregulated upon neural differentiation. Loss or shRNA depletion of WDR5B impairs cell growth and increases the fraction of non-viable cells in proliferating retinal pigment epithelial (RPE) cultures. CUT&RUN chromatin profiling in RPE and neural progenitors indicates minimal WDR5B enrichment at established WDR5 binding sites. These results suggest that WDR5 and WDR5B exhibit several divergent biological properties despite sharing a high degree of sequence homology. CUT&RUN sequencing was performed using FLAG or rabbit IgG (control) antibodies in human ARPE-19 cell lines stably expressing WDR5-FLAG or WDR5B-FLAG (2 biological replicates per condition). ARPE-19 cells were grown in Lonza XVIVO10 medium and harvested on day 8 post-seeding. CUT&RUN sequencing was also performed using WDR5, FLAG, or rabbit IgG (control) antibodies in human H9 ESC-derived neural ectoderm progenitor cells edited using CRISPR-Cas9 to endogenously express WDR5B-FLAG (2 biological replicates per condition). Neural ectoderm cells were differentiated for 6 days prior to CUT&RUN in DMEM/F12 medium containing 1X B-27, 1X N-2, 10mM nicotinamide, 10µM SB431542, and 5µM DMH1. All cells were cultured at 37C with 5% CO2.