In somatic cell reprogramming, cells must escape the somatic cell-specific gene expression program to adopt other cell fates. Here, in vitro chemical induction with RepSox generated chemically induced mammary epithelial cells (CiMECs) with milk secreting functions from goat ear fibroblasts (GEFs). Transplanted CiMECs regenerated the normal mammary gland structure with milk-secreting functions in nude mice. Single-cell RNA sequencing revealed that during the reprogramming process, GEFs may sequentially undergo embryonic ectoderm (EE)-like and different MEC developmental states and finally achieve milk secreting functions, bypassing the pluripotent state. Mechanistically, Smad3 upregulation induced by transforming growth factor β (TGFβ) receptor 1 (TGFβR1) downregulation led to GEF reprogramming into CiMECs without other reprogramming factors. The TGFβR1-Smad3 regulatory effects will provide new insight into the TGFβ signaling pathway regulation of somatic cell reprogramming. These findings suggest an innovative strategy for autogenous cell therapy for mammary gland defects and the production of transgenic mammary gland bioreactors.

在体细胞重编程中，细胞必须逃避体细胞特异性基因表达程序以适应其他细胞命运。在这里，使用 RepSox 进行体外化学诱导产生了化学诱导的乳腺上皮细胞 (CiMEC)，其具有来自山羊耳成纤维细胞 (GEF) 的泌乳功能。移植的CiMECs在裸鼠体内再生了具有泌乳功能的正常乳腺结构。单细胞RNA测序显示，在重编程过程中，GEFs可能依次经历胚胎外胚层（EE）样和不同的MEC发育状态，最终实现泌乳功能，绕过多能状态。从机制上讲，Smad3 上调由转化生长因子 β (TGFβ) 受体 1 (TGFβR1) 诱导下调导致 GEF 在没有其他重编程因素的情况下重编程为 CiMEC。TGFβR1-Smad3 调节作用将为体细胞重编程的 TGFβ 信号通路调节提供新的见解。这些发现提出了一种针对乳腺缺陷的自体细胞疗法和转基因乳腺生物反应器生产的创新策略。