The eggs of drosophilid species are characterised by the presence of dorsal appendages, which arise from the follicular epithelium. Different species display different numbers and morphologies of appendages, but little is known about how these differences arise from a morphological perspective. Now, on p. , Miriam Osterfield and colleagues compare the morphogenesis of the D. melanogaster paired appendages with appendage formation in two other species, S. pattersoni and D. funebris. In D. melanogaster, appendage morphogenesis is at least partly driven by cell-cell rearrangements between the cells that will form the floor of the appendage and neighbouring operculum cells. However, the authors find that this morphogenetic mechanism is not conserved in S. pattersoni, where eggs have variable numbers of appendages – typically five to eight. Instead, tube morphogenesis is driven by floor cell elongation: those floor cells that will form the appendage elongate dramatically without a similar exchange of neighbours. In D. funebris, both cell elongation and cell rearrangements contribute to appendage formation. That the mechanisms underlying appendage formation differ so dramatically suggests a surprising diversity in cellular behaviours during morphogenesis between even closely related species.
