Staccato/Unc-13-4 controls secretory lysosome-mediated lumen fusion during epithelial tube anastomosis.
A crucial yet ill-defined step during the development of tubular networks, such as the vasculature, is the formation of connections (anastomoses) between pre-existing lumenized tubes. By studying tracheal tube anastomosis in Drosophila melanogaster, we uncovered a key role of secretory lysosome-related organelle (LRO) trafficking in lumen fusion. We identified the conserved calcium-binding protein Unc-13-4/Staccato (Stac) and the GTPase Rab39 as critical regulators of this process. Stac and Rab39 accumulate on dynamic vesicles, which form exclusively in fusion tip cells, move in a dynein-dependent manner, and contain late-endosomal, lysosomal, and SNARE components characteristic of LROs. The GTPase Arl3 is necessary and sufficient for Stac LRO formation and promotes Stac-dependent intracellular fusion of juxtaposed apical plasma membranes, thereby forming a transcellular lumen. Concomitantly, calcium is released locally from ER exit sites and apical membrane-associated calcium increases. We propose that calcium-dependent focused activation of LRO exocytosis restricts lumen fusion to appropriate domains within tip cells.
Institute of Molecular Life Sciences and Ph.D. Program in Molecular Life Sciences, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
Sara
S
Caviglia
Max-Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, D-01307 Dresden, Germany.
Marko
M
Brankatschk
Institute of Molecular Life Sciences and Ph.D. Program in Molecular Life Sciences, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
Elisabeth J
EJ
Fischer
Max-Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, D-01307 Dresden, Germany.
Suzanne
S
Eaton
Institute of Molecular Life Sciences and Ph.D. Program in Molecular Life Sciences, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.|Institute of Neurobiology, University of Münster, Badestrasse 9, D-48149 Münster, Germany.|Cells-in-Motion Cluster of Excellence (EXC 1003 - CiM), University of Münster, D-48149 Münster, Germany.
Stefan
0000-0002-0634-3368
S
Luschnig
D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D004331:Drosophila melanogaster; D004847:Epithelial Cells / Q000166:cytology; D004848:Epithelium / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology*; D008247:Lysosomes / Q000378:metabolism*; D008561:Membrane Fusion / Q000502:physiology*; D015388:Organelles / Q000378:metabolism*; D050600:SNARE Proteins / Q000378:metabolism*
D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D050600:SNARE Proteins; C083141:phorbol ester binding protein