DGCR8 HITS-CLIP reveals novel functions for the Microprocessor

The Drosha–DGCR8, or Microprocessor, complex, is required for microRNA biogenesis. DGCR8 recognizes the RNA substrates, whereas Drosha functions as an endonuclease. High-throughput sequencing and cross-linking immunoprecipitation (HITS-CLIP) analyses reveal many other RNA targets of DGCR8 besides microRNAs, including snoRNAs, which are processed in a Drosha-independent manner, as well as long noncoding RNAs and mRNAs of protein-coding genes. The Drosha–DGCR8 complex (Microprocessor) is required for microRNA (miRNA) biogenesis. DGCR8 recognizes the RNA substrate, whereas Drosha functions as the endonuclease. Using high-throughput sequencing and cross-linking immunoprecipitation (HITS-CLIP) we identified RNA targets of DGCR8 in human cells. Unexpectedly, miRNAs were not the most abundant targets. DGCR8-bound RNAs also comprised several hundred mRNAs as well as small nucleolar RNAs (snoRNAs) and long noncoding RNAs. We found that the Microprocessor controlled the abundance of several mRNAs as well as of MALAT1. By contrast, DGCR8-mediated cleavage of snoRNAs was independent of Drosha, suggesting the involvement of DGCR8 in cellular complexes with other endonucleases. Binding of DGCR8 to cassette exons is a new mechanism for regulation of the relative abundance of alternatively spliced isoforms. These data provide insights in the complex role of DGCR8 in controlling the fate of several classes of RNAs.