Smurfs have “fused” into the asymmetric division of stem cells

Abstract

The asymmetric cell division is the way in which a stem cell divides into one daughter stem cell and one differentiated daughter cell. This process is one of the key principles of developmental biology that ensures the perpetual supply of stem cells while allowing a particular cell lineage to be populated. During Drosophila oogenesis, the fate of the daughter stem cell produced from the asymmetric division of germline stem cells (GSCs) is specified by Decapentaplegic (Dpp), but the other daughter cell has almost equal access to the Dpp signal. How Dpp signaling is inactivated in the differentiated daughter cell has been a deep mystery until a recent study, led by Dahua Chen of the Institute of Zoology, China (Xia et al., 2010), showed that the Dpp receptor, Thick vein (Tkv), is degraded specifically in the differentiated daughter cell by an HECT-domain ubiquitin E3 ligase, Smurf, in conjunction with a serine-threonine kinase Fused (Fu). This finding is as much revealing as it is surprising, because up until now Fu is considered a core member of the Hedgehog signaling pathway. Whether Fu serendipitously steps onto the turf of Dpp signaling or its regulation of Tkv degradation foretells an elaborate coordination between two important cell-cell communication systems will surely be a hot button issue for future studies.