Fleury Vincent, Watanabe Tomoko
Laboratoire de physique de la matière condensée, Ecole polytechnique/CNRS, 91128 Palaiseau cedex, France.
C R Biol. 2002 May;325(5):571-83. doi: 10.1016/s1631-0691(02)01432-4.
Understanding the growth of branching organs is an important scientific endeavour. It has crucial applications, from saving premature newborns, to repairing or even regenerating organs. Despite differences in timing and shape, branching morphogenesis of all branching organs or glands (lung, kidney, salivary, lachrymal, mammary glands, sebaceous and sweat glands, prostate, guts papillae etc.) is similar: an epithelial sheet of cells, forming a 2D layer, penetrates into a 3D mass of mesenchymal cells. Inside the epithelium, a lumen is filled with fluid. As the epithelium grows, it evolves into a branched structure. The pattern of branches is in some cases stereotypic, deterministic, and it has memory effects. We present a simple line of reasoning that predicts that viscous fingering of biological tissue will exhibit all of these features. The line of reasoning is based on the idea that surface tension selects the shape of a growing branch, as is well known in the context of moving boundary problems, except that in this case, the surface is akin to a liquid-crystal. The anisotropy of the surface tension comes from a symmetry breaking by collagen and fibroblasts. The equilibrium shape of the corresponding boundary is that of an actual fingertip, and the out-of-equilibrium shape is that of branched organs, such as the lung.
了解分支器官的生长是一项重要的科学探索。它有着至关重要的应用，从挽救早产新生儿到修复甚至再生器官。尽管在时间和形态上存在差异，但所有分支器官或腺体（肺、肾、唾液腺、泪腺、乳腺、皮脂腺和汗腺、前列腺、肠乳头等）的分支形态发生过程都是相似的：一层上皮细胞形成二维层，侵入三维间充质细胞团块。上皮内部，管腔充满液体。随着上皮生长，它演变成分支结构。在某些情况下，分支模式是刻板的、确定性的，并且具有记忆效应。我们提出了一条简单的推理思路，预测生物组织的粘性指进现象将呈现所有这些特征。这条推理思路基于这样一个观点，即表面张力决定生长分支的形状，这在移动边界问题中是众所周知的，只是在这种情况下，表面类似于液晶。表面张力的各向异性源于胶原蛋白和成纤维细胞引起的对称性破缺。相应边界的平衡形状是实际指尖的形状，而非平衡形状则是分支器官（如肺）的形状。
