title: Polarity protein Par3/Bazooka follows myosin-dependent junction repositioning.
abstract: The polarity protein Par3/Bazooka (Baz) has been established as a central component of the apical basal polarity system that determines the position of cell-cell junctions in epithelial cells. Consistent with that view, we show that shortly before gastrulation in Drosophila, Baz protein in the mesoderm is down-regulated from junctional sites in response to Snail (Sna) expression. This down-regulation leads to a specific decrease in adherens junctions without affecting other E-Cadherin pools. However, we further show that, interactions between Baz and junctions are not unidirectional. During apical constriction and the internalization of the mesoderm, down-regulation of Baz is transiently blocked as adherens junctions shift apically and are strengthened in response to tension generated by contractile actomyosin. When such junction remodeling is prevented by down-regulating myosin, Baz is lost prematurely in mesodermal epithelium. During such apical shifts, Baz is initially left behind as the junction shifts position, but then re-accumulates at the new location of the junctions. On the dorsal side of the embryo, a similar pattern of myosin activity appears to limit the basal shift in junctions normally driven by Baz that controls epithelium folding. Our results suggest a model where the sensitivity of Baz to Sna expression leads to the Sna-dependent junction disassembly required for a complete epithelium-mesenchymal transition. Meanwhile this loss of Baz-dependent junction maintenance is countered by the myosin-based mechanism which promotes an apical shift and strengthening of junctions accompanied by a transient re-positioning and maintenance of Baz proteins.
authors.affiliation: Department of Molecular Biology, Princeton University, USA.
authors.forename: Mo
authors.initials: M
authors.lastname: Weng
authors.affiliation: Department of Molecular Biology, Princeton University, USA; Howard Hughes Medical Institute, Princeton University, Princeton, NJ 08540, USA. Electronic address: efw@princeton.edu.
authors.forename: Eric
authors.initials: E
authors.lastname: Wieschaus
mesh_terms: D000205:Actomyosin / Q000378:metabolism; D022005:Adherens Junctions / Q000502:physiology*; D000818:Animals; D015536:Down-Regulation; D029721:Drosophila Proteins / Q000096:biosynthesis / Q000235:genetics*; D004331:Drosophila melanogaster / Q000196:embryology*; D058750:Epithelial-Mesenchymal Transition / Q000502:physiology; D004848:Epithelium / Q000378:metabolism; D005260:Female; D047908:Intracellular Signaling Peptides and Proteins / Q000096:biosynthesis / Q000235:genetics*; D008297:Male; D008565:Membrane Proteins / Q000235:genetics*; D008648:Mesoderm / Q000502:physiology; D000071250:Snail Family Transcription Factors / Q000096:biosynthesis*
chemical_list: D029721:Drosophila Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D000071250:Snail Family Transcription Factors; C400774:baz protein, Drosophila; C000604451:sna protein, Drosophila; D000205:Actomyosin