Long-label retention has been used by many to prove Cairns' immortal strand hypothesis and to identify potential stem cells. Here, we describe two strategies using 5-ethynl-2'-deoxyuridine (EdU) to identify and understand the distribution of long-label-retaining mammary epithelial cells during formation of the mouse mammary ductal system. First, EdU was given upon two consecutive days per week during weeks 4 through 10 and analyzed for label retention at 13 weeks of age. Alternatively, EdU was given for 14 consecutive days beginning at 28 days of age and ending at 42 days of age. Analyses were conducted at >91 days of age (13 weeks). Many more LREC were detected following the second labeling method and their distribution among the subsequently developed ducts. This finding indicated that the early-labeled cells that retained their label were distributed into portions of the gland that developed after the ending of EdU treatment (i.e. 42->91 days). These observations may have important meaning with respect to the previously demonstrated retention of regenerative capacity throughout the mouse mammary gland despite age or reproductive history. These results suggest LREC may represent long-lived progenitor cells that are responsible for mammary gland homeostasis. Additionally, these cells may act as multipotent stem cells capable of mammary gland regeneration upon random fragment transplantation into epithelium-denuded mammary fat pads.

中文翻译：

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长标签保留的乳腺上皮细胞在导管发育的早期产生并分布在整个分支导管中

许多人使用长标签保留来证明凯恩斯的永生链假说并识别潜在的干细胞。在这里，我们描述了使用 5-ethynl-2'-deoxyuridine (EdU) 来识别和了解在小鼠乳腺导管系统形成过程中长标签保留乳腺上皮细胞的分布的两种策略。首先，在第 4 周到第 10 周期间每周连续两天给予 EdU，并在 13 周龄时分析标签保留情况。或者，从 28 日龄开始到 42 日龄结束连续 14 天给予 EdU。分析是在 > 91 日龄（13 周）时进行的。在第二种标记方法及其在随后开发的导管中的分布之后，检测到更多的 LREC。这一发现表明，保留其标签的早期标记细胞分布在 EdU 治疗结束后（即 42->91 天）发育的腺体部分。这些观察结果可能对先前证明的整个小鼠乳腺的再生能力保留具有重要意义，尽管年龄或生殖史。这些结果表明 LREC 可能代表负责乳腺稳态的长寿祖细胞。此外，这些细胞可以作为多能干细胞，在随机片段移植到上皮裸露的乳腺脂肪垫中时能够再生乳腺。这些观察结果可能对先前证明的整个小鼠乳腺的再生能力保留具有重要意义，尽管年龄或生殖史。这些结果表明 LREC 可能代表负责乳腺稳态的长寿祖细胞。此外，这些细胞可以作为多能干细胞，在随机片段移植到去除上皮的乳腺脂肪垫中时能够再生乳腺。这些观察结果可能对先前证明的整个小鼠乳腺的再生能力保留具有重要意义，尽管年龄或生殖史。这些结果表明 LREC 可能代表负责乳腺稳态的长寿祖细胞。此外，这些细胞可以作为多能干细胞，在随机片段移植到上皮裸露的乳腺脂肪垫中时能够再生乳腺。