Seasonal Changes in the Expression of Molecular Markers of Stallion Germ Cells

The economic impacts of infertility and subfertility of stallions greatly influence the horse breeding industry. Self-renewal and differentiation of spermatogonial stem cells are the initial processes to maintain sperm population. About 50% of the sperm population is reduced during the non-breeding season (NBS) in stallions. Therefore, comparing the factors related to spermatogenesis during the breeding season (BS) and NBS may provide a solution to reveal the causes and remedies for subfertile/infertile stallions. It is especially pertinent to study the different protein markers during undifferentiated, differentiating, and differentiated spermatogonia. DAZL, UTF-1, and PGP9.5 are the molecular markers expressed at different stages of spermatogenesis. However, the expression pattern of these molecular markers throughout the year in stallion remains undetermined. The objectives of this study were to (1) investigate the expression pattern and localization within seminiferous tubules (2) evaluate the relative mRNA levels of these three germ cell markers in stallion testes during BS and NBS. Testicular tissues were collected during routine field castration. Immunohistochemistry was performed to compare the expression pattern and localization and qPCR analysis was performed to calculate the relative mRNA expression levels. Immunostaining of germ cells with DAZL and UTF-1 were not significantly different but PGP9.5 was significantly higher during BS. The relative mRNA levels of DAZL and PGP9.5 found significantly upregulated, however, UTF-1 observed significantly downregulated during BS. From these results, it is suggested that the proliferation of DAZL and PGP9.5 positive germ cells are gonadotropin-dependent while that of UTF-1 positive germ cells are gonadotropin-independent in stallion testes.