Horne-Badovinac Sally, Bilder David
Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, California, United States of America.
PLoS Genet. 2008 Jan;4(1):e8. doi: 10.1371/journal.pgen.0040008.
Intense investigation has identified an elaborate protein network controlling epithelial polarity. Although precise subcellular targeting of apical and basolateral determinants is required for epithelial architecture, little is known about how the individual determinant proteins become localized within the cell. Through a genetic screen for epithelial defects in the Drosophila follicle cells, we have found that the cytoplasmic Dynein motor is an essential regulator of apico-basal polarity. Our data suggest that Dynein acts through the cytoplasmic scaffolding protein Stardust (Sdt) to localize the transmembrane protein Crumbs, in part through the apical targeting of specific sdt mRNA isoforms. We have mapped the sdt mRNA localization signal to an alternatively spliced coding exon. Intriguingly, the presence or absence of this exon corresponds to a developmental switch in sdt mRNA localization in which apical transcripts are only found during early stages of epithelial development, while unlocalized transcripts predominate in mature epithelia. This work represents the first demonstration that Dynein is required for epithelial polarity and suggests that mRNA localization may have a functional role in the regulation of apico-basal organization. Moreover, we introduce a unique mechanism in which alternative splicing of a coding exon is used to control mRNA localization during development.
深入研究已确定了一个控制上皮极性的复杂蛋白质网络。尽管上皮结构需要顶端和基底外侧决定因素精确的亚细胞定位，但对于单个决定因素蛋白如何在细胞内定位却知之甚少。通过对果蝇卵泡细胞上皮缺陷进行遗传筛选，我们发现细胞质动力蛋白是顶-基极性的重要调节因子。我们的数据表明，动力蛋白通过细胞质支架蛋白星尘（Sdt）发挥作用，部分通过特定sdt mRNA亚型的顶端靶向作用来定位跨膜蛋白面包屑（Crumbs）。我们已将sdt mRNA定位信号映射到一个可变剪接的编码外显子。有趣的是，该外显子的存在与否对应于sdt mRNA定位的一个发育开关，其中顶端转录本仅在上皮发育早期出现，而未定位的转录本在成熟上皮中占主导。这项工作首次证明了动力蛋白是上皮极性所必需的，并表明mRNA定位可能在顶-基组织的调节中具有功能作用。此外，我们引入了一种独特的机制，即利用编码外显子的可变剪接在发育过程中控制mRNA定位。
