Single-cell RNA sequencing reveals novel markers of pituitary stem cells and hormone-producing cell-types

Transcription factors and signaling pathways that regulate stem cells and specialized hormone-producing cells in the pituitary gland have been the subject of intense study and have yielded a mechanistic understanding of pituitary organogenesis and disease. Yet, the regulation of stem cell proliferation and differentiation, the heterogeneity among specialized hormone-producing cells, and the role of non-endocrine cells in the gland remain important, unanswered questions. Recent advances in single-cell RNA sequencing (scRNAseq) technologies provide new avenues to address these questions. We  performed scRNAseq on approximately 13,663 cells pooled from six whole pituitary glands of 7-week-old C57BL/6 male mice. We identified pituitary endocrine and stem cells in silico, as well as other support cell-types such as endothelia, connective tissue, and red and white blood cells. Differential gene expression analyses identify known and novel markers of pituitary endocrine and stem cell populations. We demonstrate the value of scRNAseq by in vivo validation of a novel gonadotrope-enriched marker, Foxp2. We present novel scRNAseq data of in vivo pituitary tissue, including data from agnostic clustering algorithms which suggest the presence of a somatotrope subpopulation enriched in sterol/cholesterol synthesis genes. At the same time, we show that incomplete transcriptome annotation can cause false negatives on some scRNAseq platforms that only generate 3' transcript end sequences, and use in vivo data to recover reads of the pituitary transcription factor Prop1. Ultimately, scRNAseq technologies represent a significant opportunity to address longstanding questions regarding the development and function of the different populations of the pituitary gland throughout life. Overall design: 10x Chromium single-cell RNAseq of cells from pituitary glands of 7-week-old male C57BL/6 mice

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Cheung LYM, George AS, McGee SR, Daly AZ, Brinkmeier ML, Ellsworth BS, Camper SA