PAX7 expression defines germline stem cells in the adult testis
Gina M. Aloisio, Yuji Nakada, Hatice D. Saatcioglu, Christopher G. Peña, Michael D. Baker, Edward D. Tarnawa, Jishnu Mukherjee, Hema Manjunath, Abhijit Bugde, Anita L. Sengupta, James F. Amatruda, Ileana Cuevas, F. Kent Hamra, Diego H. Castrillon
Gina M. Aloisio, Yuji Nakada, Hatice D. Saatcioglu, Christopher G. Peña, Michael D. Baker, Edward D. Tarnawa, Jishnu Mukherjee, Hema Manjunath, Abhijit Bugde, Anita L. Sengupta, James F. Amatruda, Ileana Cuevas, F. Kent Hamra, Diego H. Castrillon
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Research Article

PAX7 expression defines germline stem cells in the adult testis

Abstract

Spermatogenesis is a complex, multistep process that maintains male fertility and is sustained by rare germline stem cells. Spermatogenic progression begins with spermatogonia, populations of which express distinct markers. The identity of the spermatogonial stem cell population in the undisturbed testis is controversial due to a lack of reliable and specific markers. Here we identified the transcription factor PAX7 as a specific marker of a rare subpopulation of Asingle spermatogonia in mice. PAX7+ cells were present in the testis at birth. Compared with the adult testis, PAX7+ cells constituted a much higher percentage of neonatal germ cells. Lineage tracing in healthy adult mice revealed that PAX7+ spermatogonia self-maintained and produced expanding clones that gave rise to mature spermatozoa. Interestingly, in mice subjected to chemotherapy and radiotherapy, both of which damage the vast majority of germ cells and can result in sterility, PAX7+ spermatogonia selectively survived, and their subsequent expansion contributed to the recovery of spermatogenesis. Finally, PAX7+ spermatogonia were present in the testes of a diverse set of mammals. Our data indicate that the PAX7+ subset of Asingle spermatogonia functions as robust testis stem cells that maintain fertility in normal spermatogenesis in healthy mice and mediate recovery after severe germline injury, such as occurs after cancer therapy.

Authors

Gina M. Aloisio, Yuji Nakada, Hatice D. Saatcioglu, Christopher G. Peña, Michael D. Baker, Edward D. Tarnawa, Jishnu Mukherjee, Hema Manjunath, Abhijit Bugde, Anita L. Sengupta, James F. Amatruda, Ileana Cuevas, F. Kent Hamra, Diego H. Castrillon

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Figure 4

Lineage tracing of PAX7+ descendants in Pax7-CreERT2;R26R testes.

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Lineage tracing of PAX7+ descendants in Pax7-CreERT2;R26R testes. Mice w...
Mice were treated with tamoxifen at 6 weeks of age then aged for the indicated intervals. (A) Representative clones at 4 days, 3 weeks, and 6 weeks. Dashed lines demarcate tubule borders. Arrows denote a 1-cell clone at 4 days or isolated Asingle spermatogonia at the periphery of larger clones at 6 weeks. All marker-expressing cells in these fields are considered clonal because there were no additional marked cells in the tubule. The H&E-stained section of Xgal-treated testis at 6 weeks showed a single-labeled (blue) elongate spermatid tail among many unlabeled (pink) spermatid tails in the tubular lumen. Other labeled spermatid tails were outside the field of view. Scale bars: 100 μm; 10 μm (H&E). (B) Average clone numbers in n = 4 testes. The 1-week time point may represent undercount due to difficulty in visualizing single-cell clones, or marker expression lag. Clone numbers were consistent with the presence of approximately 400 PAX7+ cells per testis and 10% recombination efficiency for Pax7-CreERT2 after tamoxifen administration (31). (C) Clone size. Red bars denote means. Larger clones were composed of large labeled zones and peripheral smaller chains including Asingle spermatogonia.