Neonatal and adult human testis defined at the single-cell level

Spermatogenesis has been well studied in rodents and invertebrates, but remains poorly understood in humans. As a step towards illuminating human spermatogenesis, we used single-cell RNA-sequencing (scRNAseq) analysis to analyze neonatal and adult human testes. Clustering analysis of neonatal testes revealed 3 germ subsets, including cells with characteristics of primordial germ cells (PGCs), and more differentiated cells with gene expression profiles similar with adult spermatogonial stem cells (SSCs). We identified markers for these neonatal subsets, including protein markers for the PGC-like (PGCL) subset. Clustering analysis of the adult testis revealed 9 germ and 3 somatic cell subsets. Among the germ cell clusters are 4 undifferentiated spermatogonia (SPG) states, each marked by specific genes. One of the SPG states has characteristics suggesting it is enriched for SSCs. We identified protein markers specific for this state, including cell-surface proteins that we used to enrich for these cells. We mapped the timeline of male germ cell development from PGCs through fetal germ cells to differentiating adult SPG stages. We also defined somatic cell subsets in the human testis and traced their developmental trajectories. Together, our data provides a blueprint for understanding the development of the male germline and supporting somatic cells in humans. The germ cell subset markers we identified are candidates to be used for clinical applications, including SSC therapy for treating infertility. Single cell sequencing from two neonatal and two adult testicular cells was performed. Cells were either enriched for ITGA6 expression or unfractionated before GEM capture