Sertoli cells are the source of stem cell factor for spermatogenesis.

Several cell types have been proposed to create the required microenvironment for spermatogenesis. However, expression patterns of the key growth factors produced by these somatic cells have not been systematically studied and no such factor has been conditionally deleted from its primary source(s), raising the question of which cell type(s) are the physiological sources of these growth factors. Here, using single-cell RNA sequencing and a series of fluorescent reporter mice, we found that stem cell factor (Scf), one of the essential growth factors for spermatogenesis, was broadly expressed in testicular stromal cells, including Sertoli, endothelial, Leydig, smooth muscle and Tcf21-CreER+ stromal cells. Both undifferentiated and differentiating spermatogonia were associated with Scf-expressing Sertoli cells in the seminiferous tubule. Conditional deletion of Scf from Sertoli cells, but not any other Scf-expressing cells, blocked the differentiation of spermatogonia, leading to complete male infertility. Conditional overexpression of Scf in Sertoli cells, but not endothelial cells, significantly increased spermatogenesis. Our data reveal the importance of anatomical localization for Sertoli cells in regulating spermatogenesis and that SCF produced specifically by Sertoli cells is essential for spermatogenesis.

Luteinizing hormone signaling restricts hematopoietic stem cell expansion during puberty.

The number and self-renewal capacity of hematopoietic stem cells (HSCs) are tightly regulated at different developmental stages. Many pathways have been implicated in regulating HSC development in cell autonomous manners; however, it remains unclear how HSCs sense and integrate developmental cues. In this study, we identified an extrinsic mechanism by which HSC number and functions are regulated during mouse puberty. We found that the HSC number in postnatal bone marrow reached homeostasis at 4 weeks after birth. Luteinizing hormone, but not downstream sex hormones, was involved in regulating HSC homeostasis during this period. Expression of luteinizing hormone receptor (Lhcgr) is highly restricted in HSCs and multipotent progenitor cells in the hematopoietic hierarchy. When Lhcgr was deleted, HSCs continued to expand even after 4 weeks after birth, leading to abnormally elevated hematopoiesis and leukocytosis. In a murine acute myeloid leukemia model, leukemia development was significantly accelerated upon Lhcgr deletion. Together, our work reveals an extrinsic counting mechanism that restricts HSC expansion during development and is physiologically important for maintaining normal hematopoiesis and inhibiting leukemogenesis.

Perivenous Stellate Cells Are the Main Source of Myofibroblasts and Cancer-Associated Fibroblasts Formed After Chronic Liver Injuries.

BACKGROUND AND AIMS: Studies of the identity and pathophysiology of fibrogenic HSCs have been hampered by a lack of genetic tools that permit specific and inducible fate-mapping of these cells in vivo. Here, by single-cell RNA sequencing of nonparenchymal cells from mouse liver, we identified transcription factor 21 (Tcf21) as a unique marker that restricted its expression to quiescent HSCs. APPROACH AND RESULTS: Tracing Tcf21+ cells by Tcf21-CreER (Cre-Estrogen Receptor fusion protein under the control of Tcf21 gene promoter) targeted ~10% of all HSCs, most of which were located at periportal and pericentral zones. These HSCs were quiescent under steady state but became activated on injuries, generating 62%-67% of all myofibroblasts in fibrotic livers and ~85% of all cancer-associated fibroblasts (CAFs) in liver tumors. Conditional deletion of Transforming Growth Factor Beta Receptor 2 (Tgfbr2) by Tcf21-CreER blocked HSC activation, compromised liver fibrosis, and inhibited liver tumor progression. CONCLUSIONS: In conclusion, Tcf21-CreER-targeted perivenous stellate cells are the main source of myofibroblasts and CAFs in chronically injured livers. TGF-ß signaling links HSC activation to liver fibrosis and tumorigenesis.