Spermatogonial kinetics in the human [TECHNIQUES AND RESOURCES REPORT]

Sara Di Persio, Rossana Saracino, Stefania Fera, Barbara Muciaccia, Valentina Esposito, Carla Boitani, Bartolomeo P. Berloco, Francesco Nudo, Gustavo Spadetta, Mario Stefanini, Dirk G. de Rooij, and Elena Vicini

The human spermatogonial compartment is essential for daily production of millions of sperm. Despite this crucial role, the molecular signature, kinetic behavior and regulation of human spermatogonia are poorly understood. Using human testis biopsies with normal spermatogenesis and studying marker protein expression, for the first time we identified different subpopulations of spermatogonia. MAGE-A4 marks all spermatogonia, KIT marks all B spermatogonia and UCLH1 all Apale-dark (Ap-d) spermatogonia. We suggest that at the start of the spermatogenic lineage there are Ap-d spermatogonia that are GFRA1^High likely including the spermatogonial stem cells. Then UTF1 becomes expressed, cells become quiescent and GFRA1 expression decreases. Finally, GFRA1 expression is lost and subsequently cells differentiate into B spermatogonia, losing UTF1 and acquiring KIT expression. Strikingly, most of human Ap-d spermatogonia are out of cell cycle and even differentiating type B spermatogonial proliferation is restricted. A novel scheme for human spermatogonial development is proposed that will facilitate further research in this field, the understanding of cases of infertility and the development of methods to increase sperm output.

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