MicroRNAs (miRNAs) are non-coding RNA molecules that regulate gene expression by binding to target mRNAs. They are primarily transcribed by RNA polymerase II and processed by Drosha and Dicer to generate mature miRNAs. This study investigates the processing of miRNAs located within introns of protein-coding genes. It was previously thought that Drosha cleaves introns after splicing, but the authors found that miRNAs can be processed from unspliced introns before splicing. This suggests that Drosha may cleave miRNA-containing introns between the splicing commitment step and the excision step, allowing both miRNA biogenesis and protein synthesis to occur from a single primary transcript. The study shows that Drosha cleavage of intronic miRNAs does not significantly affect mRNA production, indicating that splicing is not a prerequisite for miRNA processing. The results suggest that miRNA-harboring introns may be cotranscriptionally defined and physically tethered to each other, allowing efficient splicing and miRNA processing. The findings provide a novel example of eukaryotic gene organization and RNA-processing control.MicroRNAs (miRNAs) are non-coding RNA molecules that regulate gene expression by binding to target mRNAs. They are primarily transcribed by RNA polymerase II and processed by Drosha and Dicer to generate mature miRNAs. This study investigates the processing of miRNAs located within introns of protein-coding genes. It was previously thought that Drosha cleaves introns after splicing, but the authors found that miRNAs can be processed from unspliced introns before splicing. This suggests that Drosha may cleave miRNA-containing introns between the splicing commitment step and the excision step, allowing both miRNA biogenesis and protein synthesis to occur from a single primary transcript. The study shows that Drosha cleavage of intronic miRNAs does not significantly affect mRNA production, indicating that splicing is not a prerequisite for miRNA processing. The results suggest that miRNA-harboring introns may be cotranscriptionally defined and physically tethered to each other, allowing efficient splicing and miRNA processing. The findings provide a novel example of eukaryotic gene organization and RNA-processing control.