ABSTRACT
Technological improvements enable single-cell epigenetic analyses of organ development. We reasoned that high-resolution single-cell chromatin accessibility mapping would provide needed insight into the epigenetic reprogramming and transcriptional regulators involved in normal mammary gland development. Here, we provide a single-cell resource of chromatin accessibility for murine mammary development from the peak of fetal mammary stem cell (fMaSC) functional activity in late embryogenesis to the differentiation of adult basal and luminal cells. We find that the chromatin landscape within individual cells predicts both gene accessibility and transcription factor activity. The ability of single-cell chromatin profiling to separate E18 fetal mammary cells into clusters exhibiting basal-like and luminal-like chromatin features is noteworthy. Such distinctions were not evident in analyses of droplet-based single-cell transcriptomic data. We present a web application as a scientific resource for facilitating future analyses of the gene regulatory networks involved in mammary development.
Subject(s)
Cell Lineage/genetics , Chromatin/metabolism , Mammary Glands, Animal/cytology , Mammary Glands, Animal/growth & development , Single-Cell Analysis , Transcription, Genetic , Animals , Cell Differentiation/genetics , Epigenesis, Genetic , Female , Fetus/cytology , Gene Expression Regulation, Developmental , Genome , Mice , Transcription Factors/metabolismABSTRACT
Cell state reprogramming during tumor progression complicates accurate diagnosis, compromises therapeutic effectiveness, and fuels metastatic dissemination. We used chromatin accessibility assays and transcriptional profiling during mammary development as an agnostic approach to identify factors that mediate cancer cell state interconversions. We show that fetal and adult basal cells share epigenetic features consistent with multi-lineage differentiation potential. We find that DNA-binding motifs for SOX transcription factors are enriched in chromatin that is accessible in stem/progenitor cells and inaccessible in differentiated cells. In both mouse and human tumors, SOX10 expression correlates with stem/progenitor identity, dedifferentiation, and invasive characteristics. Strikingly, we demonstrate that SOX10 binds to genes that regulate neural crest cell identity, and that SOX10-positive tumor cells exhibit neural crest cell features.
Subject(s)
Breast Neoplasms/genetics , Cell Plasticity/genetics , Mammary Neoplasms, Experimental/genetics , SOXE Transcription Factors/metabolism , Adult , Animals , Breast Neoplasms/pathology , Cell Differentiation/genetics , Cell Line, Tumor/transplantation , Cell Transformation, Neoplastic/genetics , Embryo, Mammalian , Epigenesis, Genetic , Female , Gene Expression Profiling , Gene Expression Regulation, Neoplastic , Humans , Mammary Glands, Animal/growth & development , Mammary Glands, Animal/pathology , Mammary Glands, Human/growth & development , Mammary Glands, Human/pathology , Mammary Neoplasms, Experimental/pathology , Mice , Mice, Transgenic , Neural Crest/growth & development , Neural Crest/pathology , SOXE Transcription Factors/genetics , Stem Cells/pathologyABSTRACT
The search for the bipotent mammary stem cells that drive mammary development requires markers to enable their prospective isolation. There is general agreement that bipotent mouse mammary stem cells are abundant in late fetal development, but their existence in the adult is vigorously debated. Among markers useful for mammary stem cell identification, the Wnt co-receptor Lgr5 has been suggested by some to be both "necessary and sufficient" for bipotency and transplantation of adult mammary stem cell activity, though other studies disagree. Importantly, the relevance of Lgr5 to the bipotency of fetal mammary stem cells has not been studied. We show here that expression of a fluorescent protein driven by the endogenous Lgr5 promoter enables significant fetal mammary stem cell enrichment. We used lineage tracing to demonstrate embryonic cells expressing Lgr5 are bipotent, while their adult counterparts are myoepithelial restricted. Importantly, our data conclusively demonstrate that Lgr5 is dispensable for both fetal and adult mammary stem cell activity and for the development of mammary tumors.
