Rhombic organization of microvilli domains found in a cell model of the human intestine

Symmetry is rarely found on cellular surfaces. An exception is the brush border of microvilli, which are essential for the proper function of transport epithelia. In a healthy intestine, they appear densely packed as a 2D-hexagonal lattice. For in vitro testing of intestinal transport the cell line Caco-2 has been established. As reported by electron microscopy, their microvilli arrange primarily in clusters developing secondly into a 2D-hexagonal lattice. Here, atomic force microscopy (AFM) was employed under aqueous buffer conditions on Caco-2 cells, which were cultivated on permeable filter membranes for optimum differentiation. For analysis, the exact position of each microvillus was detected by computer vision; subsequent Fourier transformation yielded the type of 2D-lattice. It was confirmed, that Caco-2 cells can build a hexagonal lattice of microvilli and form clusters. Moreover, a second type of arrangement was discovered, namely a rhombic lattice, which appeared at sub-maximal densities of microvilli with (29 ± 4) microvilli / μm2. Altogether, the findings indicate the existence of a yet undescribed pattern in cellular organization.细胞表面极少呈现对称性。唯一的例外是微绒毛刷状缘（brush border），其对转运上皮（transport epithelia）的正常功能至关重要。在健康肠道中，微绒毛呈紧密排列的二维六边形晶格（2D-hexagonal lattice）结构。 针对肠道转运的体外检测研究，已建立了Caco-2细胞系（cell line Caco-2）。据电子显微镜（electron microscopy）观测报道，该细胞系的微绒毛最初以簇状排列，随后逐步形成二维六边形晶格结构。 本研究采用原子力显微镜（atomic force microscopy, AFM），在水相缓冲液（aqueous buffer）环境下对Caco-2细胞进行观测；这些细胞被培养于通透滤膜（permeable filter membranes）上以实现最优分化。分析阶段，通过计算机视觉（computer vision）技术识别每一根微绒毛的精确位置，后续经傅里叶变换（Fourier transformation）即可确定二维晶格的类型。 研究证实，Caco-2细胞可形成微绒毛的六边形晶格结构并形成簇状排列。此外，本研究还发现了第二种排列模式：菱形晶格（rhombic lattice），该结构出现在微绒毛密度未达最大值的区域，密度为(29 ± 4) 根/μm²。 综上，本研究结果表明，细胞组织中存在一种尚未被报道过的排列模式。