Trafficking through Rab11 endosomes is required for cellularization during Drosophila embryogenesis.
BACKGROUND
Embryonic cleavage leads to the formation of an epithelial layer during development. In Drosophila, the process is specialized and called cellularization. The trafficking pathways that underlie this process and that are responsible for the mobilization of membrane pools, however, remain poorly understood.


RESULTS
We provide functional evidence for the role of endocytic trafficking through Rab11 endosomes in remobilizing vesicular membrane pools to ensure lateral membrane growth. Part of the membrane stems from endocytosed apical material. Mutants in the endocytic regulators rab5 and shibire/dynamin inhibit basal-lateral membrane growth, and apical endocytosis is blocked in shibire mutants. In addition, shibire controls vesicular trafficking through Rab11-positive endosomes. In shibire mutants, the transmembrane protein Neurotactin follows the secretory pathway normally but is not properly inserted in the plasma membrane and accumulates instead in Rab11 subapical endosomes. Consistent with a direct role of shibire in vesicular trafficking through Rab11 endosomes, Shibire is enriched in this compartment. Moreover, we show by electron microscopy the large accumulation of intracellular coated pits on subapical endocytic structures in shibire mutants. Finally, we show that Rab11 is essential for membrane growth and invagination during cellularization.


CONCLUSIONS
Together, the data show that endocytic trafficking is required for basal-lateral membrane growth during cellularization. We identify Rab11 endosomes as key trafficking intermediates that control vesicle exocytosis and membrane growth during cellularization. This pathway may be required in other morphogenetic processes characterized by the growth of a membrane domain.
Laboratoire de Génétique et de Physiologie du Développement, Institut de Biologie du Développement de Marseille, France.
Anne
A
Pelissier
Jean-Paul
JP
Chauvin
Thomas
T
Lecuit
D000818:Animals; D002455:Cell Division / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism*; D004330:Drosophila / Q000196:embryology*; D029721:Drosophila Proteins / Q000378:metabolism; D034281:Dynamins / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000648:ultrastructure; D011992:Endosomes / Q000378:metabolism / Q000502:physiology*; D004727:Endothelium / Q000502:physiology; D006652:Histological Techniques; D008845:Microinjections; D008854:Microscopy, Electron; D016133:Polymerase Chain Reaction; D013696:Temperature; D020691:rab GTP-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D020696:rab5 GTP-Binding Proteins / Q000378:metabolism; D000099193:rab11 GTP-Binding Proteins
D029721:Drosophila Proteins; D034281:Dynamins; D020691:rab GTP-Binding Proteins; D020696:rab5 GTP-Binding Proteins; D000099193:rab11 GTP-Binding Proteins; C439628:shi protein, Drosophila