Rap1 and Canoe/afadin are essential for establishment of apical-basal polarity in the Drosophila embryo.
The establishment and maintenance of apical-basal cell polarity is critical for assembling epithelia and maintaining organ architecture. Drosophila embryos provide a superb model. In the current view, apically positioned Bazooka/Par3 is the initial polarity cue as cells form during cellularization. Bazooka then helps to position both adherens junctions and atypical protein kinase C (aPKC). Although a polarized cytoskeleton is critical for Bazooka positioning, proteins mediating this remained unknown. We found that the small GTPase Rap1 and the actin-junctional linker Canoe/afadin are essential for polarity establishment, as both adherens junctions and Bazooka are mispositioned in their absence. Rap1 and Canoe do not simply organize the cytoskeleton, as actin and microtubules become properly polarized in their absence. Canoe can recruit Bazooka when ectopically expressed, but they do not obligatorily colocalize. Rap1 and Canoe play continuing roles in Bazooka localization during gastrulation, but other polarity cues partially restore apical Bazooka in the absence of Rap1 or Canoe. We next tested the current linear model for polarity establishment. Both Bazooka and aPKC regulate Canoe localization despite being "downstream" of Canoe. Further, Rap1, Bazooka, and aPKC, but not Canoe, regulate columnar cell shape. These data reshape our view, suggesting that polarity establishment is regulated by a protein network rather than a linear pathway.
Department of Biology, University of North Carolina, Chapel Hill, NC, USA.
Wangsun
W
Choi
Nathan J
NJ
Harris
Kaelyn D
KD
Sumigray
Mark
M
Peifer
D022005:Adherens Junctions / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D016764:Cell Polarity; D048430:Cell Shape; D003599:Cytoskeleton / Q000378:metabolism; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000196:embryology / Q000235:genetics / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000196:embryology / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D018613:Microscopy, Confocal; D008954:Models, Biological; D009154:Mutation; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D020827:rap1 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
D029721:Drosophila Proteins; D047908:Intracellular Signaling Peptides and Proteins; C400774:baz protein, Drosophila; C092747:cno protein, Drosophila; D049452:Green Fluorescent Proteins; C115015:PKC-3 protein; D011493:Protein Kinase C; D020827:rap1 GTP-Binding Proteins