Spermatogonial stem cell organization in felid testis as revealed by Dolichos biflorus lectin

Spermatogonial stem cells are being exploited in many species as a tool to recover fertility, but may also be used to manipulate the genetic pool. Whatever the purpose, these cells must be fully characterized and easily identifiable, and our goal was to improve this procedure in the domestic cat, used as an animal model for endangered felid species and for some human diseases/physiological processes. We have therefore screened several markers that might be used to distinguish and study the undifferentiated spermatogonia population in situ and in vitro via immunohistochemistry applied to tissue sections and whole mounts of the domestic cat seminiferous tubules. Our results show that, although they label the cytoplasm and nucleus of gonocytes and spermatogonia in pre-pubertal animals, PGP9.5 and FoxO1 cannot be considered markers of undifferentiated spermatogonia in adult animals, as almost all spermatogonia, namely type A and B, express these proteins. Nonetheless, the Dolichos biflorus agglutinin (DBA lectin) was able to label the cell surface and cytoplasm of a small type A spermatogonial population in the adult animals. Analysis of the number and distribution of the DBA-labeled cells showed they were present in low number, which did not vary with epithelium seminiferous stage. Morphometric analysis revealed that DBA-labeled cells present tropism to a peculiar area of the seminiferous tubules, namely the area in direct contact with Leydig cells. Whole mounts of DBA-stained seminiferous tubules revealed the arrangement of DBA-stained cells in small clones up to eight cells. Noteworthy, the clonal cells presented variable staining intensity suggesting the existence of asymmetric distribution of O-glycosylated proteins within each clone. Our results strongly suggest that the DBA lectin is a marker of undifferentiated spermatogonia in domestic cat, and illustrate the peculiar characteristics of spermatogonial stem cell development and organization in this species.