The cell cycle of stem cells is tightly controlled so that they can divide throughout life and respond to challenges such as injury and starvation. Defects in this control could result in abnormal tissue maintenance or cancer. Now, Hannele Ruohola-Baker and co-workers analyse cell division in Drosophila germline stem cells (GSCs) and reveal that the cell cycle regulator Dacapo is suppressed by microRNAs (miRNAs); in turn, the miRNAs might be controlled by insulin(). This group has previously shown that the miRNA pathway regulates Dacapo in GSCs. Here,the authors demonstrate that several miRNAs can target the dacapo3′ UTR directly, and that mutations in these miRNAs lead to abnormal GSC divisions. The dacapo 3′ UTR also responds to insulin receptor(InR), but not to TGF-β, signalling (two pathways known to regulate GCS divisions), and InR-deficient GSCs display defects resembling those of miRNA pathway mutants. Based on these and other findings, the authors propose that insulin regulates the division of GSCs through miRNAs and Dacapo.
