229 LONG-TERM PROPAGATION AND CRYOPRESERVATION OF CAT SPERMATOGONIAL STEM CELLS

Abstract

Spermatogonial stem cells (SSC) are unique adult stem cells that reside within the seminiferous tubules of the testis. As stem cells, SSC maintain the ability to self-replicate, providing a potentially unlimited supply of cells and an alternate source for preservation of the male genome. While self-renewing, long-term SSC culture has been achieved in mice, there is virtually no information regarding culture requirements of felid SSC. Therefore, the objectives of this study were to (1) evaluate the ability of 3 feeder cell lines to support germ cell colony establishment in domestic cats (Felis catus), and (2) assess long-term culture using the best feeder(s). Cells isolated enzymatically from peripubertal cat testes (n = 4) and enriched by differential plating were cultured on mouse embryonic fibroblasts (STO line), mouse-derived C166 endothelial cells, and primary cat fetal fibroblasts (cFF). Colony morphology was assessed every other day and immunocytochemistry (ICC) was performed to investigate expression of SSC markers. At 5 days in vitro (DIV), a cluster forming activity assay was used to estimate the number of SSC supported by each feeder cell line. Differences among treatments were compared using Tukey-Kramer adjustment for pair-wise mean comparisons. Data were expressed as mean cluster number ± SE per 10⁵ cells input. When cultured on STO feeders, cat germ cells were distributed as individual cells. On both C166 cells and cFF feeders, germ cell clumps (morphologically consistent with SSC colonies in other species) were observed. Immunocytochemistry revealed that the single germ cells present on STO feeders were positive for UCHL1 and weakly expressed PLZF and OCT4. Cells within the germ cell clumps on C166 cells and cFF co-expressed all 3 SSC markers. The C166 cells supported a higher number of germ cell clusters (77.4 ± 13.8) compared with STO (3.5 ± 1.1, P = 0.0003) or cFF (22.7 ± 1.0, P = 0.0024). Therefore, subsequent subculture experiments were performed exclusively with C166 feeder layers. Cultures from 2 donors were passaged at 12 DIV and periodically as needed thereafter. Germ cell clumps consistently reestablished following each subculture and immunocytochemistry analysis confirmed maintenance of all 3 SSC markers. Cells were also positive for alkaline phosphatase activity. Cells that had been cryopreserved in culture medium with 5% (vol/vol) dimethyl sulphoxide after144 DIV (7 passages) were thawed and cultured for an additional 18 days. These cells continued to express SSC markers and form germ cell clusters. Taken together, these data demonstrate that C166 feeder cells can facilitate colony establishment and in vitro propagation of germ cell clumps in the domestic cat. This represents an important first step towards attainment and optimization of a long-term SSC culture system in the cat. This system would provide a mechanism to explore regulation of spermatogenesis, test species-specific drugs, and produce transgenic biomedical models.