Localization and Function of Pals1 Associated Tight Junction Protein in Drosophila is Regulated by Two Distinct Apical Complexes [Cell Biology]

April 6th, 2015 by Sen, A., Sun, R., Krahn, M. P.

The transmembrane protein Crumbs (Crb) and its intracellular adaptor protein Pals1 (Stardust, Sdt in Drosophila) play a crucial role in the establishment and maintenance of apical-basal polarity in epithelial cells in various organisms. In contrast, the multiple-PDZ-domain containing protein PATJ, which has been described to form a complex with Crb/Sdt, is not essential for apical basal polarity or for the stability of the Crb/Sdt complex in the Drosophila epidermis. Here we show that in the embryonic epidermis Sdt is essential for the correct subcellular localization of PATJ in differentiated epithelial cells but not during cellularization. Consistently, the L27-domain of PATJ is crucial for the correct localization and function of the protein. Our data further indicate that the four PDZ domains of PATJ function to a large extent in redundancy regulating the proteins function. Interestingly the PATJ-Sdt heterodimer is not only recruited to the apical cell-cell contacts by binding to Crb but depends on functional Bazooka (Baz). However biochemical experiments show that PATJ associates with both complexes, the Baz-Sdt and the Crb-Sdt complex in the mature epithelium of the embryonic epidermis, suggesting a role of these two complexes for PATJs function during development of Drosophila.
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