Abstract
Apical-basal polarity is a fundamental property of animal tissues. The Drosophila embryo provides an outstanding model for defining mechanisms that initiate and maintain polarity. Polarity is initiated during cellularization, when cell-cell adherens junctions are positioned at the future boundary of apical and basolateral domains. Polarity maintenance then involves complementary and antagonistic interplay between apical and basal polarity complexes. The Scribble/Dlg module is well-known for promoting basolateral identity during polarity maintenance. Here we report a surprising role for the Scribble/Dlg module in polarity initiation, placing it at the top of the network that positions adherens junctions. Scribble and Dlg are enriched in nascent adherens junctions and are essential for adherens junction positioning and supermolecular assembly. They also play a role in basal junction assembly. We test hypotheses for the underlying mechanisms. Our data suggest that the Scribble/Dlg module plays multiple roles in polarity initiation, via Par-1-dependent and independent mechanisms. Different domains of Scribble contribute to these distinct roles. Together these data reveal novel roles for Scribble/Dlg as master scaffolds regulating the assembly of distinct junctional complexes at different times and places.
Footnotes
Abbreviations used: AJ, adherens junction; Arm, Armadillo; Baz, Bazooka; BJ, basal junction; Cno, Canoe; DE-cad, Drosophila E-cadherin; Dlg, Discs Large; GEF, guanine nucleotide exchange factor; GFP, green fluorescent protein; Lgl, Lethal giant larvae; LRR, leucine rich repeats; MIP, maximum intensity projection; Nrt, Neurotactin; PDZ domain, post synaptic density, disc large, and zonula occludens-1 domain; SAJ, spot adherens junction; SJ, septate junctions; shRNA, short hairpin RNA; Scrib, Scribble; TCJ, tricellular junctions; WT, wildtype
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