PAX7 expression defines germline stem cells in the adult testis
Gina M. Aloisio, … , F. Kent Hamra, Diego H. Castrillon
Gina M. Aloisio, … , F. Kent Hamra, Diego H. Castrillon
Published August 18, 2014
Citation Information: J Clin Invest. 2014;124(9):3929-3944. https://doi.org/10.1172/JCI75943.
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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 5

Lineage tracing of PAX7+ descendants in Pax7-CreERT2;mT/mG testes.

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Lineage tracing of PAX7+ descendants in Pax7-CreERT2;mT/mG testes. Adult...
Adult males were treated with tamoxifen at 6 weeks of age, then aged for the indicated intervals. (A) Clone morphology by confocal microscopy of isolated tubules. Representative Asingle, Apair, Aal4, and Aal8 clones 1 week after tamoxifen administration are shown. Other panels show larger clones at 6 weeks; arrows indicate detached Asingle spermatogonia that were part of larger clones. Inset: elongated spermatid tails in tubular lumen. Clones >500 cells could not be reliably counted. Larger clones were associated with smaller separate chains at their periphery, including Asingle spermatogonia. The few 1-cell clones at 6–16 weeks represent Asingle spermatogonia too distant from the nearest clone to be confidently identified as part of it, but may reflect long-distance migration. Green motile sperm were observed in the epididymis. (B) Clone morphology in tissue sections (16 weeks after tamoxifen). PAX7+ descendants gave rise to all spermatogenic stages, as evidenced by circumferential full-thickness labeling of all spermatogenic stages throughout the tubule. Tissue sections were counterstained with DAPI. (C) Labeled sperm from epididymis showing bright green fluorescence and characteristic hook morphology. The majority of sperm did not exhibit fluorescence, and control epididymides did not contain spermatozoa with comparable fluorescence (i.e., the signal shown is not background autofluorescence of sperm). (D) Average clone number in n = 4 testes. Clone numbers did not decrease over time. (E) Clone size. Red bars denote means. Larger clones included detached smaller chains and Asingle spermatogonia. Scale bars: 25 μm.