干细胞是尚未分化成熟的细胞，除胚胎干细胞外，多数干细胞常常“命中注定”只能成长为某一种特定的细胞。但刊登在19日出版的英国《自然》杂志上的一项最新研究成果显示，只要改变成长环境，来自胸腺的干细胞也可以“转行”变为毛囊细胞。这对于研究器官组织再生具有重要意义。
据英国爱丁堡大学发布的公告，该校研究人员和瑞士同行进行的这项研究成功改变了实验鼠胸腺干细胞的“命运”。胸腺是存在于人和许多动物胸部的一个器官，它是免疫细胞T细胞的生成地，在免疫系统中发挥着重要作用。
研究人员首先培养出实验鼠胸腺干细胞，然后将它转移到适宜皮肤毛囊细胞生长的环境中培养，结果发现这些胸腺干细胞在新环境中逐渐改变了自己的基因特征，越来越像皮肤毛囊的干细胞。
在这种环境中培育一段时间后，这些细胞被移植到正在生长的皮肤中，结果它们拥有了像毛囊细胞一样供养和修复毛发的能力，且表现出色。天然毛囊干细胞成长后只有三个星期的修复毛发能力，而这些胸腺干细胞“转行”后拥有长达一年的修复毛发能力。
据介绍，大部分动物的胚胎分为外胚层、中胚层和内胚层三个胚层，外胚层成长为皮肤和神经等，中胚层成长为肌肉、骨骼和血液等，内胚层成长为肠道、肝脏和胸腺等器官。过去一直认为这三个胚层的细胞间存在无法逾越的鸿沟，但本次研究证明来自内胚层的胸腺干细胞也可以变为本应属于外胚层的皮肤毛囊细胞，显示不同胚层细胞间的区分并不绝对。
爱丁堡大学的克莱尔·布莱克本博士说，这些胸腺干细胞在适宜毛囊干细胞成长的环境里完全改变了原定的成长轨道，从而启发研究人员使用适宜其他器官干细胞成长的环境，探索能否培育出所需的器官细胞，这对研究器官组织再生具有重要意义。（生物谷Bioon.com）
生物谷推荐原文出处：
Nature doi:10.1038/nature09269
Microenvironmental reprogramming of thymic epithelial cells to skin multipotent stem cells
Paola Bonfanti,Stéphanie Claudinot,Alessandro W. Amici,Alison Farley,C. Clare Blackburn& Yann Barrandon
The thymus develops from the third pharyngeal pouch of the anterior gut and provides the necessary environment for thymopoiesis (the process by which thymocytes differentiate into mature T lymphocytes) and the establishment and maintenance of self-tolerance1, 2, 3. It contains thymic epithelial cells (TECs) that form a complex three-dimensional network organized in cortical and medullary compartments, the organization of which is notably different from simple or stratified epithelia4. TECs have an essential role in the generation of self-tolerant thymocytes through expression of the autoimmune regulator Aire5, 6, but the mechanisms involved in the specification and maintenance of TECs remain unclear7, 8, 9. Despite the different embryological origins of thymus and skin (endodermal and ectodermal, respectively), some cells of the thymic medulla express stratified-epithelium markers10, 11, 12, interpreted as promiscuous gene expression. Here we show that the thymus of the rat contains a population of clonogenic TECs that can be extensively cultured while conserving the capacity to integrate in a thymic epithelial network and to express major histocompatibility complex class II (MHC II) molecules and Aire. These cells can irreversibly adopt the fate of hair follicle multipotent stem cells when exposed to an inductive skin microenvironment; this change in fate is correlated with robust changes in gene expression. Hence, microenvironmental cues are sufficient here to re-direct epithelial cell fate, allowing crossing of primitive germ layer boundaries and an increase in potency13.
