An alarming new trend is sweeping the nation: men in skinny jeans. The fad has gone so far that even miRNAs have started squeezing themselves into tight genes, so to speak. According to a new paper by researchers from Tel Aviv University and Harvard, it seems miRNA genes preferentially wedge themselves within the introns of short genes compared with their relaxed-fit counterparts.
Most mammalian miRNAs arise from genomic duplication events, many occuring within introns of transcriptional units. To better understand how miRNA genes expand through the genome, the investigators examined the distribution of intronic miRNAs. Among their findings:
- Although miRNA genes are more frequently located in introns of long genes, their occurrence within introns of short genes is much higher than expected by random genomic integration. (Short genes usually have short introns.) This is true for human, mice, fly, and worm intronic miRNAs.
- Knocking down pre-mRNA splicing factors boosted the expression of miRNAs harbored in short but not long introns.
- The lengths of miRNA-hosting introns were more conserved between human and mouse than the lengths of non-hosting introns.
The team proposes a model in which splicing inhibits the expression of miRNAs located in short introns, possibly through steric hindrance by splicing factors at exon-intron boundaries. Integration of miRNA genes into short introns could be evolutionarily favorable because it allows mild regulation of potential target genes. Over time, as target genes gain or lose binding sites for the miRNA, stronger expression could evolve.
Get the skinny on all the details at Bioinformatics, February 2010.