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First published online March 8, 2006
doi: 10.1242/10.1242/jcs.02898

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The PAR-aPKC system: lessons in polarity

Department of Molecular Biology, Yokohama City University Graduate School of Medical Science, 3-9 Fuku-ura, Kanazawa-ku, Yokohama 236-0004, Japan

View larger version (37K): [in a new window]   Fig. 1. Various types of cell polarity in which the PAR-aPKC system is involved. (A) Anterior-posterior polarization of the C. elegans zygote just after fertilization. (B) Anterior-posterior polarizations (early and late) of Drosophila oocytes during oogenesis. (C) Development of apical-basal polarity of Drosophila blastoderm epithelium formed just beneath the egg membrane. (D) Apical-basal polarity observed in mammalian cultured epithelial cells. (E) Polarization of mammalian primary-cultured astrocytes to the front during directed migration. (F) Polarization of a mammalian primary-cultured neuron that specifies one of the immature neurites as an axon. Red lines and dots represent the localization of the aPKC complex, whereas blue lines indicate the PAR-1 distribution. The distribution of PAR-1 in the Drosophila embryonic ectoderm and its derivative neuroblasts, as well as in mammalian astrocytes and neurons has not been clearly described. Gray ovals represent nuclei, green lines represent microtubules.

View larger version (22K): [in a new window]   Fig. 2. Antagonistic interactions between oppositely localized PAR-aPKC system components that lead to the establishment of complementary membrane domains. (A) C. elegans zygote. (B) Drosophila/mammalian epithelial cells. In epithelial cells, the involvement of additional evolutionarily conserved polarity proteins (Crb/Pals1/PATJ and Lgl/Scrib/Dlg) has also been demonstrated. The components of the PAR-aPKC system are shown in black boxes. Red indicates anterior or apical polarity proteins, whereas blue indicates posterior or basolateral polarity proteins. Green indicates proteins that do not show clear asymmetric localization. Red- and blue-colored boxes enclose proteins categorized into functional groups whose localizations are mutually dependent (the requirement of PATJ for the localization of Crb and Sdt/Pals1 has been shown only in MDCK cells not in Drosophila) (Pielage et al., 2003; Shin et al., 2005). The role of PAR-4 in these interactions has not been well clarified, although its close functional relationship with PAR-1 has been demonstrated in both types of cell (see text).

View larger version (31K): [in a new window]   Fig. 3. The protein-protein interaction network involving polarity proteins in mammalian epithelial cells. The key shows the protein domains involved. Black arrows indicate direct physical interactions, whereas orange dotted arrows indicate phosphorylation. Putative interactions suggested from the data obtained using Drosophila epithelia are indicated by gray dotted arrows with question marks. The involvement of PAR-5/14-3-3 is not shown in this figure to avoid complication, although PAR-5/14-3-3 has been demonstrated to interact with PAR-1b and PAR-3. PAR-1b is suggested to phosphorylate microtubule-associated proteins (MAPs) and thereby affect microtubule stability (Drewes et al., 1997; Cohen et al., 2004). AJ, adherens junction; TJ, tight junction.

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