The fusome and microtubules enrich Par-1 in the oocyte, where it effects polarization in conjunction with Par-3, BicD, Egl, and dynein.
After its specification, the Drosophila oocyte undergoes a critical polarization event that involves a reorganization of the microtubules (MT) and relocalization of the determinant Orb within the oocyte. This polarization requires Par-1 kinase and the PDZ-containing Par-3 homolog, Bazooka (Baz). Par-1 has been observed on the fusome, which degenerates before the onset of oocyte polarization. How Par-1 acts to polarize the oocyte has been unclear. Here we show that Par-1 becomes restricted to the oocyte in a MT-dependent fashion after disappearance of the fusome. At the time of polarization, the kinase itself and the determinant BicaudalD (BicD) are relocalized from the anterior to the posterior of the oocyte. Par-1 and BicD are interdependent and require MT and the minus end-directed motor Dynein for their relocalization. We show that baz is required for Par-1 relocalization within the oocyte and that the distributions of Baz and Par-1 in the Drosophila oocyte are complementary and strikingly reminiscent of the two PAR proteins in the C. elegans embryo. We propose that, through the combined actions of the fusome, MT, and Baz, Par-1 is selectively enriched and localized within the oocyte, where, in conjunction with BicD, Egalitarian (Egl), and Dynein, it acts on the MT cytoskeleton to effect polarization.
Vaccari
Thomas
T
Developmental Biology Programme, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany.
Ephrussi
Anne
A
D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D016764:Cell Polarity / Q000502:physiology*; D003599:Cytoskeleton / Q000648:ultrastructure*; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D004331:Drosophila melanogaster / Q000166:cytology / Q000235:genetics / Q000502:physiology*; D004398:Dyneins / Q000235:genetics / Q000502:physiology*; D004527:Egg Proteins / Q000235:genetics / Q000502:physiology*; D038362:Glycogen Synthase Kinase 3; D047908:Intracellular Signaling Peptides and Proteins; D008870:Microtubules / Q000502:physiology*; D020409:Molecular Motor Proteins; D009865:Oocytes / Q000378:metabolism / Q000648:ultrastructure*; D009866:Oogenesis; D015388:Organelles / Q000648:ultrastructure*; D011494:Protein Kinases / Q000235:genetics / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases; D016601:RNA-Binding Proteins / Q000378:metabolism
C061998:BicD protein, Drosophila; D002352:Carrier Proteins; D029721:Drosophila Proteins; D004527:Egg Proteins; D047908:Intracellular Signaling Peptides and Proteins; D020409:Molecular Motor Proteins; D016601:RNA-Binding Proteins; C400774:baz protein, Drosophila; C089932:orb protein, Drosophila; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D038362:Glycogen Synthase Kinase 3; C472496:Par-1 protein, Drosophila; D004398:Dyneins