Dev101444 2549..2558

Multicellular rosettes have recently been appreciated as important cellular intermediates that are observed during the formation of diverse organ systems. These rosettes are polarized, transient epithelial structures that sometimes recapitulate the form of the adult organ. Rosette formation has been studied in various developmental contexts, such as in the zebrafish lateral line primordium, the vertebrate pancreas, the Drosophila epithelium and retina, as well as in theadult neural stemcell niche.Thesestudieshave revealed that the cytoskeletal rearrangements responsible for rosette formation appear to be conserved. By contrast, the extracellular cues that trigger these rearrangements in vivo are less well understood and aremore diverse. Here, we review recent studies of the genetic regulation and cellular transitions involved in rosette formation. We discuss and compare specific models for rosette formation and highlight outstanding questions in the field.