Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA 02115, USA.
Proc Natl Acad Sci U S A. 2012 Mar 6;109(10):3932-7. doi: 10.1073/pnas.1113890109. Epub 2012 Feb 21.
Lifelong self-renewal of the adult intestinal epithelium requires the activity of stem cells located in mucosal crypts. Lgr5 and Bmi1 are two molecular markers of crypt-cell populations that replenish all lineages over time and hence function as stem cells. Intestinal stem cells require Wnt signaling, but the understanding of their cellular niche is incomplete. Lgr5-expressing crypt base columnar cells (CBCs) reside deep in the crypt, mingled among mature Paneth cells that are well positioned for short-range signaling. Partial lineage ablation previously had implied that Paneth cells are nonessential constituents of the stem-cell niche, but recently their absence was reported to interfere with Lgr5(+) CBCs, resurrecting an appealing idea. However, previous mouse models failed to remove Paneth cells completely or permanently; defining the intestinal stem-cell niche requires clarity with respect to the Paneth cell role. We find that Lgr5(+) cells with stem-cell activity cluster in future crypts early in life, before Paneth cells develop. We also crossed conditional Atoh1(-/-) mice, which lack Paneth cells entirely, with Lgr5(GFP) mice to visualize Lgr5(+) CBCs and to track their stem-cell function. In the sustained absence of Paneth cells, Lgr5(+) CBCs occupied the full crypt base, proliferated briskly, and generated differentiated progeny over many months. Gene expression in fluorescence-sorted Lgr5(+) CBCs reflected intact Wnt signaling despite the loss of Paneth cells. Thus, Paneth cells are dispensable for survival, proliferation, and stem-cell activity of CBCs, and direct contact with Lgr5-nonexpressing cells is not essential for CBC function.
成年肠道上皮细胞的终身自我更新需要位于黏膜隐窝中的干细胞的活性。Lgr5 和 Bmi1 是两种隐窝细胞群体的分子标记物，它们随着时间的推移补充所有谱系，因此作为干细胞发挥作用。肠道干细胞需要 Wnt 信号，但对其细胞生态位的理解并不完整。Lgr5 表达的隐窝基底柱状细胞（CBC）位于隐窝深处，与成熟的 Paneth 细胞混合在一起，这些细胞位于短距离信号传递的理想位置。以前的部分谱系消融实验暗示 Paneth 细胞不是干细胞生态位的必需组成部分，但最近有报道称它们的缺失会干扰 Lgr5(+) CBC，从而重新提出了一个吸引人的想法。然而，以前的小鼠模型未能完全或永久性地去除 Paneth 细胞；定义肠道干细胞生态位需要明确 Paneth 细胞的作用。我们发现具有干细胞活性的 Lgr5(+)细胞在生命早期，即在 Paneth 细胞发育之前，聚集在未来的隐窝中。我们还将条件性 Atoh1(-/-)小鼠（完全缺乏 Paneth 细胞）与 Lgr5(GFP)小鼠进行杂交，以可视化 Lgr5(+) CBC 并追踪其干细胞功能。在 Paneth 细胞持续缺失的情况下，Lgr5(+) CBC 占据了整个隐窝底部，快速增殖，并在多个月内产生分化后代。荧光分选的 Lgr5(+) CBC 中的基因表达反映了 Wnt 信号的完整性，尽管 Paneth 细胞缺失。因此，Paneth 细胞对于 CBC 的存活、增殖和干细胞活性是可有可无的，并且与 Lgr5 不表达细胞的直接接触对于 CBC 功能不是必需的。
