The study by Antony Rodriguez, Sam Griffiths-Jones, Jennifer L. Ashurst, and Allan Bradley from the Wellcome Trust Sanger Institute aimed to identify the transcriptional modes of mammalian microRNAs (miRNAs) by annotating their genomic positions in the human and mouse genomes. They found that 161 out of 232 known mammalian miRNAs overlap with defined transcription units (TUs). These miRNAs were identified in introns of 90 protein-coding genes and in both introns and exons of 66 mRNA-like noncoding RNAs (mncRNAs). The authors also identified novel families of miRNAs based on host gene identity and curated the expression patterns of miRNA host genes to illustrate spatial, temporal, and physiological regulation of miRNA expression. The findings suggest that miRNAs are transcribed in parallel with their host transcripts, and that the two different transcription classes of miRNAs ('exonic' and 'intronic') may require slightly different biogenesis mechanisms. The study highlights the complex nature of miRNA biogenesis and the potential for parallel transcription in mammals.The study by Antony Rodriguez, Sam Griffiths-Jones, Jennifer L. Ashurst, and Allan Bradley from the Wellcome Trust Sanger Institute aimed to identify the transcriptional modes of mammalian microRNAs (miRNAs) by annotating their genomic positions in the human and mouse genomes. They found that 161 out of 232 known mammalian miRNAs overlap with defined transcription units (TUs). These miRNAs were identified in introns of 90 protein-coding genes and in both introns and exons of 66 mRNA-like noncoding RNAs (mncRNAs). The authors also identified novel families of miRNAs based on host gene identity and curated the expression patterns of miRNA host genes to illustrate spatial, temporal, and physiological regulation of miRNA expression. The findings suggest that miRNAs are transcribed in parallel with their host transcripts, and that the two different transcription classes of miRNAs ('exonic' and 'intronic') may require slightly different biogenesis mechanisms. The study highlights the complex nature of miRNA biogenesis and the potential for parallel transcription in mammals.