Department of Medicine, University of California Los Angeles, 10833 LeConte Avenue, Los Angeles, CA 90095-1679, USA.
Circ Res. 2012 Feb 17;110(4):551-9. doi: 10.1161/CIRCRESAHA.111.255927. Epub 2012 Jan 5.
Left-right (LR) asymmetry is ubiquitous in animal development. Cytoskeletal chirality was recently reported to specify LR asymmetry in embryogenesis, suggesting that LR asymmetry in tissue morphogenesis is coordinated by single- or multi-cell organizers. Thus, to organize LR asymmetry at multiscale levels of morphogenesis, cells with chirality must also be present in adequate numbers. However, observation of LR asymmetry is rarely reported in cultured cells.
Using cultured vascular mesenchymal cells, we tested whether LR asymmetry occurs at the single cell level and in self-organized multicellular structures.
Using micropatterning, immunofluorescence revealed that adult vascular cells polarized rightward and accumulated stress fibers at an unbiased mechanical interface between adhesive and nonadhesive substrates. Green fluorescent protein transfection revealed that the cells each turned rightward at the interface, aligning into a coherent orientation at 20° relative to the interface axis at confluence. During the subsequent aggregation stage, time-lapse videomicroscopy showed that cells migrated along the same 20° angle into neighboring aggregates, resulting in a macroscale structure with LR asymmetry as parallel, diagonal stripes evenly spaced throughout the culture. Removal of substrate interface by shadow mask-plating, or inhibition of Rho kinase or nonmuscle myosin attenuated stress fiber accumulation and abrogated LR asymmetry of both single-cell polarity and multicellular coherence, suggesting that the interface triggers asymmetry via cytoskeletal mechanics. Examination of other cell types suggests that LR asymmetry is cell-type specific.
Our results show that adult stem cells retain inherent LR asymmetry that elicits de novo macroscale tissue morphogenesis, indicating that mechanical induction is required for cellular LR specification.
左右（LR）不对称性在动物发育中普遍存在。最近有研究报道细胞骨架的手性特异性决定了胚胎发生中的 LR 不对称性，这表明组织形态发生中的 LR 不对称性是由单细胞或多细胞组织者协调的。因此，为了在形态发生的多尺度水平上组织 LR 不对称性，具有手性的细胞也必须以足够的数量存在。然而，在培养的细胞中很少观察到 LR 不对称性。
使用培养的血管间充质细胞，我们测试了 LR 不对称性是否发生在单细胞水平和自组织的多细胞结构中。
使用微图案化，免疫荧光显示成年血管细胞在无偏力学界面（粘附和非粘附基底之间）向右极化并积累应力纤维。绿色荧光蛋白转染显示细胞在界面处各自向右转向，在汇合时相对于界面轴以 20°的角度排列成一致的取向。在随后的聚集阶段，延时视频显微镜显示细胞沿着相同的 20°角迁移到相邻的聚集物中，导致宏观结构具有 LR 不对称性，平行的、对角线的条纹均匀地分布在整个培养物中。通过阴影掩模板去除基底界面，或抑制 Rho 激酶或非肌肉肌球蛋白会削弱应力纤维的积累并消除单细胞极性和多细胞一致性的 LR 不对称性，表明界面通过细胞骨架力学触发不对称性。对其他细胞类型的检查表明，LR 不对称性是细胞类型特异性的。
我们的结果表明，成年干细胞保留了固有 LR 不对称性，引发了新的宏观组织形态发生，表明机械诱导是细胞 LR 特异性所必需的。
