Expression patterns of cell-surface molecules on male germ line stem cells during postnatal mouse development

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Abstract
Spermatogonial stem cells (SSCs) are stem cells of the male germ line. In mice, SSCs are quiescent at birth but actively proliferate during the first postnatal week, while they rarely divide in adult, suggesting an age-dependent difference in SSC characteristics. As an approach to evaluate this possibility, we studied the expression pattern of cell-surface molecules on neonatal, pup, and adult mouse SSCs. Using immunomagnetic cell sorting, testis cells were selected for the expression of α6 integrin, αv integrin, c-kit receptor tyrosine kinase (Kit), or a binding subunit of glial-cell-line-derived neurotrophic factor (GDNF) receptor, GFRα1. Selected cells were assayed for their stem cell activity using spermatogonial transplantation. The results showed that SSCs expressed α6 integrin, but not αv integrin and Kit, regardless of age. The SSC activity in pup GFRα1+ cells was higher than that in adult and neonatal cells, indicating that the expression pattern of GFRα1 varied age-dependently. To evaluate if SSCs show an age-dependent difference in their response to GDNF, we cultured highly enriched pup and adult SSCs with GDNF: we could not observe such an age-dependent difference in vitro. In addition, we failed to immunologically detect the expression of two types of GDNF receptor signaling subunits on SSCs. These results indicate that SSCs may change the expression patterns of cell-surface molecules during postnatal development, and suggest that GDNF receptor molecules may not be abundantly or specifically expressed in the in vivo population of mouse SSCs. Mol. Reprod. Dev.