Heterogeneity within the mouse mammary epithelium and potential lineage relationships have been recently explored by single-cell RNA profiling. To further understand how cellular diversity changes during mammary ontogeny, we profiled single cells from nine different developmental stages spanning late embryogenesis, early postnatal, prepuberty, adult, mid-pregnancy, late-pregnancy, and post-involution, as well as the transcriptomes of micro-dissected terminal end buds (TEBs) and subtending ducts during puberty. The single cell transcriptomes of 132,599 mammary epithelial cells from 9 different developmental stages were determined on the 10x Genomics Chromium platform, and integrative analyses were performed to compare specific time points. The mammary rudiment at E18.5 closely aligned with the basal lineage, while prepubertal epithelial cells exhibited lineage segregation but to a less differentiated state than their adult counterparts. Comparison of micro-dissected TEBs versus ducts showed that luminal cells within TEBs harbored intermediate expression profiles. Ductal basal cells exhibited increased chromatin accessibility of luminal genes compared to their TEB counterparts suggesting that lineage-specific chromatin is established within the subtending ducts during puberty. An integrative analysis of five stages spanning the pregnancy cycle revealed distinct stage-specific profiles and the presence of cycling basal, mixed-lineage, and 'late' alveolar intermediates in pregnancy. Moreover, a number of intermediates were uncovered along the basal-luminal progenitor cell axis, suggesting a continuum of alveolar-restricted progenitor states. This extended single cell transcriptome atlas of mouse mammary epithelial cells provides the most complete coverage for mammary epithelial cells during morphogenesis to date. Together with chromatin accessibility analysis of TEB structures, it represents a valuable framework for understanding developmental decisions within the mouse mammary gland.

中文翻译：

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小鼠乳腺上皮细胞发育过程中的单细胞转录组图谱

最近通过单细胞 RNA 分析探索了小鼠乳腺上皮内的异质性和潜在的谱系关系。为了进一步了解乳腺个体发育过程中细胞多样性如何变化，我们分析了来自九个不同发育阶段的单个细胞，包括胚胎发生晚期、产后早期、青春期前、成年、妊娠中期、妊娠晚期和复旧后，以及显微解剖末端芽 (TEB) 和青春期对着导管。在 10x Genomics Chromium 平台上确定了来自 9 个不同发育阶段的 132,599 个乳腺上皮细胞的单细胞转录组，并进行了综合分析以比较特定时间点。E18.5 处的乳腺发育与基底谱系紧密对齐，而青春期前上皮细胞表现出谱系分离，但分化程度低于成年细胞。微解剖 TEB 与导管的比较表明 TEB 内的管腔细胞具有中间表达谱。与 TEB 对应物相比，导管基底细胞表现出腔基因的染色质可及性增加，这表明在青春期在对向导管内建立了谱系特异性染色质。对跨越妊娠周期的五个阶段的综合分析揭示了不同的阶段特异性特征以及妊娠期循环基础、混合谱系和“晚期”肺泡中间体的存在。此外，沿基底管腔祖细胞轴发现了许多中间体，表明存在肺泡受限祖细胞状态的连续体。这种扩展的小鼠乳腺上皮细胞单细胞转录组图谱为迄今为止形态发生过程中的乳腺上皮细胞提供了最完整的覆盖。连同 TEB 结构的染色质可及性分析，它代表了理解小鼠乳腺内发育决策的宝贵框架。