Germinal centers (brown) are abnormal in mice lacking miR-155 (bottom).
RAJEWSKY/AAAS
Rather than coding for proteins, miRNAs decrease protein levels by binding to their mRNA targets. Since their discovery in worms, researchers have wondered whether miRNAs simply fine-tune the genome's work or have large-scale effects of their own.
The first reports of mice lacking specific miRNAs suggest their effects are wide and strong. Antony Rodriguez, Allan Bradley (Sanger Institute, London, UK), and colleagues knocked out the gene coding for miR-155, which is active in the immune system and is up-regulated in lymphomas. The mice had defective T cell responses, were unable to fight off infection, and displayed lung tissue scarring seen in autoimmune diseases.
The same miRNA was also deleted by To-Ha...
