MicroRNA Biogenesis Takes Another Single Hit from Microsatellite Instability

In this issue of Cancer Cell, Melo et al. show that mutation of a single allele of the Exportin-5 gene (XPO5) suffices to depress microRNA (miRNA) levels and promote tumorigenesis. Thus, XPO5 joins the ranks of DICER and TRBP as a haploinsufficient tumor suppressor in the miRNA biogenesis pathway.