Sabherwal Nitin, Tsutsui Akiko, Hodge Sarah, Wei Jun, Chalmers Andrew D, Papalopulu Nancy
Faculty of Life Sciences, Michael Smith Building, University of Manchester, Manchester, UK.
Development. 2009 Aug;136(16):2767-77. doi: 10.1242/dev.034454.
During neurogenesis in Xenopus, apicobasally polarised superficial and non-polar deep cells take up different fates: deep cells become primary neurons while superficial cells stay as progenitors. It is not known whether the proteins that affect cell polarity also affect cell fate and how membrane polarity information may be transmitted to the nucleus. Here, we examine the role of the polarity components, apically enriched aPKC and basolateral Lgl2, in primary neurogenesis. We report that a membrane-tethered form of aPKC (aPKC-CAAX) suppresses primary neurogenesis and promotes cell proliferation. Unexpectedly, both endogenous aPKC and aPKC-CAAX show some nuclear localisation. A constitutively active aPKC fused to a nuclear localisation signal has the same phenotypic effect as aPKC-CAAX in that it suppresses neurogenesis and enhances proliferation. Conversely, inhibiting endogenous aPKC with a dominant-negative form that is restricted to the nucleus enhances primary neurogenesis. These observations suggest that aPKC has a function in the nucleus that is important for cell fate specification during primary neurogenesis. In a complementary experiment, overexpressing basolateral Lgl2 causes depolarisation and internalisation of superficial cells, which form ectopic neurons when supplemented with a proneural factor. These findings suggest that both aPKC and Lgl2 affect cell fate, but that aPKC is a nuclear determinant itself that might shuttle from the membrane to the nucleus to control cell proliferation and fate; loss of epithelial cell polarity by Lgl2 overexpression changes the position of the cells and is permissive for a change in cell fate.
在非洲爪蟾的神经发生过程中，顶基极化的表层细胞和非极化的深层细胞会分化出不同的命运：深层细胞成为初级神经元，而表层细胞则保持为祖细胞。目前尚不清楚影响细胞极性的蛋白质是否也会影响细胞命运，以及膜极性信息是如何传递到细胞核的。在这里，我们研究了极性成分——顶端富集的非典型蛋白激酶C（aPKC）和基底外侧的Lgl2——在初级神经发生中的作用。我们报告称，一种膜锚定形式的aPKC（aPKC-CAAX）会抑制初级神经发生并促进细胞增殖。出乎意料的是，内源性aPKC和aPKC-CAAX都表现出一定程度的核定位。一种与核定位信号融合的组成型活性aPKC与aPKC-CAAX具有相同的表型效应，即它会抑制神经发生并增强增殖。相反，用一种局限于细胞核的显性负性形式抑制内源性aPKC会增强初级神经发生。这些观察结果表明，aPKC在细胞核中具有一种功能，这对于初级神经发生过程中的细胞命运决定很重要。在一项补充实验中，过表达基底外侧的Lgl2会导致表层细胞去极化并内化，当添加一种神经前体因子时，这些细胞会形成异位神经元。这些发现表明，aPKC和Lgl2都影响细胞命运，但aPKC本身是一种核决定因素，它可能从膜穿梭到细胞核以控制细胞增殖和命运；Lgl2过表达导致上皮细胞极性丧失，改变了细胞的位置，并允许细胞命运发生改变。
