Doerflinger Hélène, Benton Richard, Shulman Joshua M, St Johnston Daniel
The Wellcome Trust/Cancer Research UK Institute and the Department of Genetics, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK.
Development. 2003 Sep;130(17):3965-75. doi: 10.1242/dev.00616.
The PAR-1 kinase plays a conserved role in cell polarity in C. elegans, Drosophila and mammals. We have investigated the role of PAR-1 in epithelial polarity by generating null mutant clones in the Drosophila follicular epithelium. Large clones show defects in apicobasal membrane polarity, but small clones induced later in development usually have a normal membrane polarity. However, all cells that lack PAR-1 accumulate spectrin and F-actin laterally, and show a strong increase in the density of microtubules. This is consistent with the observation that the mammalian PAR-1 homologues, the MARKs, dramatically reduce the number of microtubules, when overexpressed in tissue culture cells. The MARKs have been proposed to destabilize microtubules by inhibiting the stabilizing activity of the Tau family of microtubule-associated proteins. This is not the case in Drosophila, however, as null mutations in the single tau family member in the genome have no effect on the microtubule organisation in the follicle cells. Furthermore, PAR-1 activity stabilises microtubules, as microtubules in mutant cells depolymerise much more rapidly after cold or colcemid treatments. Loss of PAR-1 also disrupts the basal localisation of the microtubule plus ends, which are mislocalised to the centre of mutant cells. Thus, Drosophila PAR-1 regulates the density, stability and apicobasal organisation of microtubules. Although the direct targets of PAR-1 are unknown, we suggest that it functions by regulating the plus ends, possibly by capping them at the basal cortex.
PAR-1激酶在秀丽隐杆线虫、果蝇和哺乳动物的细胞极性中发挥着保守作用。我们通过在果蝇卵泡上皮中产生无功能突变克隆，研究了PAR-1在上皮极性中的作用。大克隆显示出顶基膜极性缺陷，但在发育后期诱导产生的小克隆通常具有正常的膜极性。然而，所有缺乏PAR-1的细胞都会在侧面积累血影蛋白和F-肌动蛋白，并显示微管密度显著增加。这与以下观察结果一致：当在组织培养细胞中过表达时，哺乳动物PAR-1的同源物MARKs会显著减少微管数量。有人提出MARKs通过抑制微管相关蛋白Tau家族的稳定活性来使微管不稳定。然而，在果蝇中并非如此，因为基因组中单个Tau家族成员的无功能突变对卵泡细胞中的微管组织没有影响。此外，PAR-1活性可稳定微管，因为突变细胞中的微管在冷处理或秋水仙酰胺处理后解聚得更快。PAR-1的缺失还会破坏微管正端的基部定位，这些正端会错误定位到突变细胞的中心。因此，果蝇PAR-1调节微管的密度、稳定性和顶基组织。虽然PAR-1的直接靶点尚不清楚，但我们认为它可能通过调节正端来发挥作用，可能是通过在基部皮层对其进行封端。
