A majority of the layer V neurons showed superior accumulation of GM130, which was not significantly affected in aPKC deletion mice. aPKC deletion mice did not show apparent cell loss/degeneration in the brain. In addition, neuronal orientation/distribution seemed to be unaffected. Thus, despite the polarity complex disruption, neuronal deletion of aPKC does not induce obvious cell loss or disorientation in mouse brains Sigma-1 receptor antagonist 3 after cell differentiation. == Introduction == In mammals, neuronal cells are polarized in multiple actions of cell differentiation. These include apical-basal polarity of neuronal progenitor epithelial cells, asymmetric division of the progenitors, directed cell migration, axon-dendrite specification and dendritic spine formation. These cell polarizations are fundamental to proper development of the central nervous system (CNS). Atypical protein kinase C (aPKC) is usually a Ser/Thr kinase that is structurally different from other common PKC subfamily kinases; that is, it lacks binding regions for calcium and phorbol ester in its regulatory domain name, but contains a protein binding PB1 domain name at its N-terminus[1]. aPKC forms an evolutionarily conserved protein complex with the PDZ-containing proteins PAR-3 and PAR-6, and it localizes asymmetrically within a cell to regulate polarization. This has been observed in various types of cells, such asC. elegansone-cell embryos,Drosophilaepidermis and mammalian epithelial cells[2][4]. aPKC also forms a complex with Lgl, a protein that contains WD repeats. This complex forms independently of PAR-3 and regulates aPKC/PAR-3/PAR-6-mediated polarization of epithelial cells[5][8]. Recent studies of gene knockout or knockdown in mice have established thein vivosignificance of aPKC and PAR-3 for epithelial tissue morphogenesis and its maintenance in mammals[9][14]. Genetic studies usingDrosophilahave further identified critical roles of aPKC/PAR-3/PAR-6 and Lgl in CNS development through the regulation of asymmetric division of neuronal progenitors (neuroblasts)[15][17]. Previously, we found that conditional knockout of an aPKC isoformaPKCin mice using a nestin-cre transgene induces disruption of apical-basal polarity of neuronal progenitor cells (neuroepithelial cells) in mouse brain cortex[18]. Although the role of aPKC in neuronal progenitor differentiation was not clarified by this study, possibly because gene knockout was done at a relatively late Sigma-1 receptor antagonist 3 stage (E15), knockdown of PAR-3 at earlier stages (E1213) enhances neuronal progenitor differentiation whereas ectopic expression of PAR-3 or PAR-6 suppresses it in mouse brains[19],[20]. In contrast, knockout of the Lgl isoform Lgl-1 suppresses progenitor differentiation and induces its continuous proliferation, leading to neoplasia formation[21], suggesting that neuronal progenitor differentiation is usually differentially regulated by PAR-3 and Lgl-1 in mammals. The importance of aPKC for neural progenitor proliferation/differentiation is usually shown during neurogenesis in Xenopus[22],[23]and zebrafish[24]embryos. As for neuronal migration, overexpression of the PAR-6 isoform PAR-6 has been shown to suppress migration of cerebellar granule neurons by disturbing cytoskeletal organization[25],[26]. Thus, aPKC and/or its interactors are involved in multiple actions of CNS development from progenitor maintenance/differentiation to cell migration by regulating cell polarization. Studies usingin vitrocultured rat hippocampal neurons further suggest the involvement of aPKC/PAR-3/PAR-6 in later stages of differentiation[27],[28]. One of them is axon specification, during which these proteins localize to the tip of the growing Mmp27 axon and regulate axonal growth by interacting with several molecules such as KIF3A, APC and Tiam1[29][32]. In addition, TGF- signaling and Smurf1 E3 ligase regulate PAR-6 by its phosphorylation and degradation, respectively, and play a Sigma-1 receptor antagonist 3 role in axonal growth of cortical neurons during mouse brain development[33],[34]. Lgl-1 has also been shown to regulate axonal growth of rat cortical neuronsin vivo[35]. PAR-3, aPKC and PAR-6 are required for dendritic spine morphogenesis inin-vitrocultured hippocampal neurons[36],[37], and the potentialin vivosignificance of this is suggested by evidence that BAI1 interacts with PAR-3 to recruit it to dendritic spines in mice[38]. In addition, analysis of mutant zebrafish has revealed that aPKC is required for dendritic specification of Purkinje cells during development[39]. Thus, although these observations contradict those observed inDrosophila[40], at least in mammals (and possibly also in zebrafish), aPKC and its interactors are involved in axon/dendrite specification and morphogenesis in later stages of neuronal differentiation. In contrast to the significance of aPKC and its interactors for neuronal differentiation during CNS development, their roles in neuronal maintenance after CNS development remain unknown. To.