201 TRANSPLANTATION OF SSEA-1+ AND SSEA-4+ SPERMATOGONIAL CELL SUBPOPULATIONS IN UNTREATED SEXUALLY IMMATURE DOMESTIC CATS

Abstract

Captive breeding efforts in felids, including assisted reproduction techniques, have had varied success depending on species. Spermatogonial stem cells (SSC), comprising a small percentage of germ cells in the testis, are progenitor cells with the ability to both self-renew and differentiate into spermatozoa throughout the life of the male. Manipulation of SSC for transplantation (SSCT) may allow the propagation of genetically important males, as demonstrated by the production of ocelot sperm following transplantation of ocelot mixed germ cells to domestic cat testes (Silva et al. 2012 J. Androl. 33, 264–276). Using specific cell surface markers, SSC have been isolated from mixed germ cells in several other species for SSCT, culture, and studying germ cell biology; however, expression may differ with species. Using the domestic cat as a model for exotic felids, we recently began evaluating the expression of surface markers in feline SSC. Previously, we determined that pluripotent markers SSEA-1, SSEA-4, TRA-1–60, and TRA-1–81 were more specific to cat spermatogonia than SSC surface markers GFRα1 and GPR125 used in other species, with SSEA-1 and SSEA-4 expressed in the fewest cells (Powell et al. 2011 Reprod. Fertil. Dev. 24, 221–222; Powell et al. 2012 Reprod. Fertil. Dev. 25, 290–291). Our current goal was to 1) confirm the presence of SSC within SSEA-1+ and SSEA-4+ cell populations by the ability to colonize following SSCT; 2) compare the effectiveness of transplanting SSC purified by flow cytometry versus mixed germ cells; and 3) show that depletion of endogenous germ cells before SSCT, usually performed by irradiation or chemotherapy in other studies, is not necessary when using sexually immature recipients. Mixed germ cells from 8 to 12 adult testes were pooled, stained for SSEA-1 or SSEA-4, and sorted by flow cytometry. SSEA-1+, SSEA-4+, or mixed germ cells were then labelled with the membrane dye PKH26 (Sigma MINI26) and injected into the testes of six 5-month-old and six 6-month-old cats at the site of the external rete testis after carefully microdissecting the head of the epididymis away from the testis. Injections contained an average of 230 000 sorted or 10 × 10⁶ mixed germ cells suspended in 80 μL of DMEM/F12 + 3 μL of Trypan Blue (T8154, Sigma, St. Louis, MO, USA). Testes were harvested 10 to 12 weeks post-SSCT and bisected, half snap-frozen for later cryosectioning and the other half enzymatically digested to loosen seminiferous tubules for immediate evaluation. Fluorescence was detected in the testes of both 6-month-old males that received injections of mixed germ cells, one 6-month-old male injected with SSEA-4+ cells, and two 5-month-old males, one injected with SSEA-4+ cells and one with SSEA-1+ cells. Results indicate that SSC are found in both SSEA-1+ and SSEA-4+ cell populations, but that purification of SSC is not necessary for successful SSCT. Additionally, SSC colonization in cats is possible without depletion of endogenous cells in sexually immature recipients.