题译：单细胞RNA测序鉴定出非洲爪蟾蜍尾巴再生的组织细胞

1. 实验设计

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比较能够尾部再生和不能尾部再生的蝌蚪进行单细胞测序。

regeneration-competent and -incompetent tadpoles by collecting either intact tails or tails at various stages after amputation

将所有样品时期单细胞数据进行整合聚类分析。

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作者期望找到与尾部再生特异的多能干细胞类群，遗憾的是通过注释细胞类群，没有发现这一类群。唯一发现截肢后新出现的细胞类群是motor neuron–like cell type。

We found no evidence for the emergence of a multipotent progenitor population during regeneration, nor did we observe intermediate cell states reflective of transdifferentiation, results which are consistent with those of lineage-tracing studies.

是否表明非洲爪蟾蜍幼体尾巴再生响应类群无法通过单细胞RNA揭示呢？

2. ROC类群的发现和再生过程的功能验证

自认为这篇文章一个重要的转折点是下面这张附图(之前看了好几遍文章主图，没有看到作者如何过度到ROC类群的发现)。

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作者比较了不同类群细胞随截肢后时间的变化过程，与不能尾部再生的蝌蚪相比，表皮细胞群受此截肢和再生变量因子的响应(注意看红色圈类群变化)，然后作者把该类群定义为Regeneration organizating cell (ROC)。

Surveying the range of single-cell data, we found that the most significant cell-type change specific to regeneration was related to a previously unidentified cell type of the epidermis (fig. S4), whichwedesignatedas the regenerationorganizing cell (ROC).

3. Relocalization of ROCs forms the specialized wound epidermis

非洲爪蟾数据：Xenbase(http://www.xenbase.org/entry/)

分析单细胞Marker基因，找到Lef1在尾巴再生表达。细胞消除实验(cell ablation)消除ROC细胞，导致尾巴截肢后再生能力丧失。

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4. Ligands and Recptors are required for regeneration

配体和受体之间的互作在再生过程中发挥重要作用。ROC细胞群表达配体，受体在祖细胞群表达，提示ROC可能作为启动再生的信号中心。

Ligands of signaling pathways that are known to be required for regeneration and that increase
proliferating cell numbers, such as FGF (15), BMP (5, 21), WNT (15), NOTCH (5), and TGFb (20), are simultaneously expressedinROCs but not in any other cell type. In contrast, receptors for these pathways are mostly expressed in progenitor cell types.In contrast, receptors for these pathways are mostly expressed in progenitor cell types.

作者进一步使用嫁接手段，证明表皮细胞中ROC的作用。

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