Mostov Keith, Brakeman Paul, Datta Anirban, Gassama Ama, Katz Leonid, Kim Minji, Leroy Pascale, Levin Max, Liu Kathleen, Martin Fernando, O'Brien Lucy E, Verges Marcel, Su Tao, Tang Kitty, Tanimizu Naoki, Yamaji Toshiyuki, Yu Wei
Department of Anatomy, University of California, San Francisco 94143-2140, USA.
Novartis Found Symp. 2005;269:193-200; discussion 200-5, 223-30.
The kidney is primarily comprised of highly polarized epithelial cells. Much has been learned recently about the mechanisms of epithelial polarization. However, in most experimental systems the orientation of this polarity is determined by external cues, such as growth of epithelial cells on a filter support. When Madin-Darby canine kidney (MDCK) cells are grown instead in a three-dimensional (3D) collagen gel, the cells form hollow cysts lined by a monolayer of epithelial cells, with their apical surfaces all facing the central lumen. We have found that expression of a dominant-negative (DN) form of the small GTPase Rac1 causes an inversion of epithelial polarity, such that the apical surface of the cells instead faces the periphery of the cyst. This indicates that the establishment of polarity and the orientation of polarity can be experimentally separated by growing cells in a 3D collagen gel, where there is no filter support to provide an external cue for orientation. DN Rac1 causes a defect in the assembly of laminin into its normal basement membrane network, and addition of a high concentration of exogenous laminin rescues the inversion of polarity caused by DN Rac1.
肾脏主要由高度极化的上皮细胞组成。最近，人们对上皮极化的机制有了很多了解。然而，在大多数实验系统中，这种极性的方向是由外部线索决定的，比如上皮细胞在滤膜支架上的生长情况。当将马-达二氏犬肾（MDCK）细胞培养在三维（3D）胶原凝胶中时，细胞会形成由单层上皮细胞排列而成的中空囊肿，其顶端表面都朝向中央管腔。我们发现，小GTP酶Rac1的显性负性（DN）形式的表达会导致上皮极性反转，使得细胞的顶端表面反而朝向囊肿的周边。这表明，通过在没有滤膜支架提供外部方向线索的3D胶原凝胶中培养细胞，极性的建立和极性的方向可以在实验中被分开。DN Rac1会导致层粘连蛋白组装到其正常基底膜网络中出现缺陷，添加高浓度的外源性层粘连蛋白可以挽救由DN Rac1引起的极性反转。
