Abstract
During morphogenesis, remodelling of cell shape requires the expansion or contraction of plasma membrane domains. Here we identify a mechanism underlying the restructuring of the apical surface during epithelial morphogenesis in Drosophila. We show that the retraction of villous protrusions and subsequent apical plasma membrane flattening is an endocytosis-driven morphogenetic process. Quantitation of endogenously tagged GFP::Rab5 dynamics reveals a massive increase in apical endocytosis that correlates with changes in apical morphology. This increase is accompanied by the formation of tubular plasma membrane invaginations that serve as platforms for the de novo generation of Rab5-positive endosomes. We identify the Rab5-effector Rabankyrin-5 as a regulator of this pathway and demonstrate that blocking dynamin activity results in the complete inhibition of tubular endocytosis, in the disappearance of Rab5 endosomes, and in the inhibition of surface flattening. These data collectively demonstrate a requirement for endocytosis in morphogenetic remodelling during epithelial development.
Highlights
During morphogenesis, remodelling of cell shape requires the expansion or contraction of plasma membrane domains
total internal reflection fluorescence (TIRF)-M is exceptionally well suited for following membrane dynamics with high spatio-temporal resolution, as it relies upon an evanescent wave that exclusively illuminates a region in close proximity (10–200 nm) to the coverslip[22]
In summary, our data demonstrate that apical surface flattening is a dynamin-dependent process associated with the dynamic regulation and functional re-organization of both endocytosis and endosome biogenesis
Summary
During morphogenesis, remodelling of cell shape requires the expansion or contraction of plasma membrane domains. We identify the Rab5-effector Rabankyrin-5 as a regulator of this pathway and demonstrate that blocking dynamin activity results in the complete inhibition of tubular endocytosis, in the disappearance of Rab[5] endosomes, and in the inhibition of surface flattening These data collectively demonstrate a requirement for endocytosis in morphogenetic remodelling during epithelial development. At the beginning of cellularization, the apical surface is rich in highly dynamic membrane protrusions that undergo a progressive, stereotypical retraction and flattening as cellularization proceeds[16] This change in apical morphology is concomitant with a corresponding change in the organization of the underlying actin cytoskeleton and the establishment of adherens junctions that serve to interconnect the cellular epithelium. Mutations in the proto-oncogenic kinase Abelson, a key regulator of adherens junction stability and actin organization, result in an excess of actin polymerization in membrane protrusions and a corresponding delay in surface flattening[17]
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