219 ISOLATION AND CHARACTERIZATION OF DOMESTIC CAT SPERMATOGONIAL CELLS

Abstract

Spermatogonial stem cells (SSC) have the capacity for self-renewal and the potential of producing progenitor spermatogonia that will differentiate into spermatozoa. SSC transplantation may be a valuable alternative for the propagation of genetically important males and preservation of endangered wild felids, as recently demonstrated by the production of ocelot spermatozoa after the xeno-transplantation of a mixed germ cell population into the testis of a domestic cat (Silva et al. 2011 J. Androl.). SSC are in low numbers in the testis and have been isolated in different mammalian species by using specific cell surface markers; however, the expression of SSC-surface markers in feline species has not been characterised. In the present study, testes of domestic cats were obtained from veterinary clinics. The selected testes (n = 4) ranged in size from 1.3 to 2.0 cm in length. To obtain a suspension of a mixed population of spermatogonial cells, seminiferous tubules were enzymatically dissociated using two digestion steps followed by dual filtration through 100-μm and 40-μm nylon mesh filters and a final separation over a 5-layer Percoll™ density gradient (35, 30, 27.5, 25 and 20%). Spermatogonial cells were morphologically identified by their characteristic large round nucleus with a homogenous appearance in the bands formed at the 30%, 27.5% and 25% layers. The mean number of cells/testis collected was ∼13 × 10⁶ ± 12.2, with an overall percentage of live cells of 97%. After isolation, cells were fixed with 4% PFA, blocked overnight and stained with primary antibodies specific for SSC-surface markers (CD49f, CD9, C-Kit, GFRα1, GPR125 and Thy-1) and pluripotent stage-specific embryonic antigen markers (SSEA-1 and SSEA-4). Fluorescence microscopy showed a positive expression of GFRα1, GPR125 and C-Kit, but not for CD49f, CD9, or Thy-1. It also revealed that a low number of cells were positive for SSEA-1 and SSEA-4. For further characterisation, molecular detection of the pluripotent gene Oct-4 and the germ cell-specific genes BOLL, DAZL and VASA was performed in germ cells isolated from one testis of four individuals. For RT-qPCR, the Cells-to-cDNA™ II kit (Ambion) was used to produce cDNA from an aliquot of ∼30 000 cells directly after isolation. RT-qPCR showed that none had detectable levels of Oct-4 within the range of the standard. Three of the four testes expressed all three germ cell-specific genes, BOLL, DAZL and VASA, while only VASA was detected in the remaining testis. These results suggest that cat SSCs and spermatogonial cells express some of the SSC markers tested. However, the positive expression of SSEA-1 and SSEA-4 in a low number of cells further supports the stem cell-like state of cat SSCs and that these markers can be used in dual staining for purifying cat SSCs from a mixed germ cell population by fluorescence-activated cell sorting.