Phenotypic and Molecular Characterization of Domestic Cat (Felis catus) Spermatogonial Stem Cells

In many mammalian species, surface markers have been used to obtain enriched populations of spermatogonial stem cells (SSCs) for assisted reproduction and other applications; however, little is known about the expression patterns of feline SSCs. In this study, we assessed expression of the SSC surface markers commonly used in other species, KIT, ITGA6, CD9, GFRalpha1, ADGRA3, and THY1, in addition to the less frequently used pluripotent markers TRA-1-60, TRA-1-81, SSEA-1, and SSEA-4 in SSCs of both prepubertal and adult domestic cats (Felis catus). To further characterize cat SSCs, we sorted cells using SSC-specific markers and evaluated the expression of the pluripotent transcription factors NANOG, POU5F1, and SOX2 and the proto-oncogene MYC within these populations. We concluded that SSC surface markers used in other mammalian species were not specific for identifying cat SSCs. However, the pluripotent markers we evaluated were more specific to cat spermatogonia, and the presence of SSEA-1 and SSEA-4 in fewer and primarily individual cells suggests that these two markers may be used for enrichment of cat SSCs. The expression of pluripotent transcription factors at mRNA level by single-stained cells positive for SSEA-4 and by dual-stained cells positive for both GFRalpha1 and SSEA-4 reflects the undifferentiated stage of cat SSCs. The absence of transcription factors in double-stained cells positive for only one marker implies the loss of the stem cell-like identity with the loss of either GFRalpha1 or SSEA-4. Further investigation is warranted to elucidate the biological characteristics of these spermatogonial subpopulations.