Association of ASIP/mPAR‐3 with adherens junctions of mouse neuroepithelial cells

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Abstract
Polarity proteins play fundamental roles in asymmetric cell division, which is essential for the production of different types of cells in multicellular organisms. Here, we explore the localization of atypical PKC isotype-specific interacting protein (ASIP), a mammalian homologue of the Caenorhabditis elegans polarity protein PAR-3, in embryonic neural tissues. Although ASIP is localized on tight junctions in cultured epithelial cells, it localizes on adherens junctions outlined by β-catenin and afadin at the luminal surface, an apical end of the neuroepithelium in developing mouse central nervous systems. Mammalian homologues of other C. elegans polarity proteins, mPAR-6 and aPKC, also localize in the adherens junctions. In dorsal root ganglia of the peripheral nervous system, ASIP is found predominantly in the cytoplasm of ganglion cells. In dividing preneural cells at the ventricular (luminal) surface of the embryonic telencephalon, ASIP localize in adherence junctions of luminal surface regardless of the axis of cell division. Therefore, only the daughter cell facing the lumen (apical daughter) may inherit ASIP when the division plate is oriented parallel to the surface. Given the roles of Bazooka, a Drosophila homologue of ASIP/PAR-3, in the asymmetric division of the Drosophila neuroblast, these observations suggest that ASIP, along with other polarity proteins and adherens junction proteins, plays an important role in neural cell differentiation by means of asymmetric cell division.