Roles of Enhancer RNAs in RANKL-induced Osteoclast Differentiation Identified by Genome-wide Cap-analysis of Gene Expression using CRISPR/Cas9.

Bidirectional transcription has been proposed to play a role associated with enhancer activity. Transcripts called enhancer RNAs (eRNAs) play important roles in gene regulation; however, their roles in osteoclasts are unknown. To analyse eRNAs in osteoclasts comprehensively, we used cap-analysis of gene expression (CAGE) to detect adjacent transcription start sites (TSSs) that were distant from promoters for protein-coding gene expression. When comparing bidirectional TSSs between osteoclast precursors and osteoclasts, we found that bidirectional TSSs were located in the 5'-flanking regions of the Nrp2 and Dcstamp genes. We also detected bidirectional TSSs in the intron region of the Nfatc1 gene. To investigate the role of bidirectional transcription in osteoclasts, we performed loss of function analyses using the CRISPR/Cas9 system. Targeted deletion of the DNA regions between the bidirectional TSSs led to decreased expression of the bidirectional transcripts, as well as the protein-coding RNAs of Nrp2, Dcstamp, and Nfatc1, suggesting that these transcripts act as eRNAs. Furthermore, osteoclast differentiation was impaired by targeted deletion of bidirectional eRNA regions. The combined results show that eRNAs play important roles in osteoclastogenic gene regulation, and may therefore provide novel insights to elucidate the transcriptional mechanisms that control osteoclast differentiation.