Characterization of male germ cell markers in canine testis

Spermatogenesis begins at puberty and continues throughout a male's life. This process is initiated and maintained by spermatogonial stem cells in the seminiferous tubules, and these cells produce haploid spermatozoa. Markers of male germ cells have been fully identified in rodents, including mice and rats, but not in canines. To characterize the canine male germ cells, histological and immunohistochemical analyses were performed, using prepubertal (1-3-month-old), early pubertal (4-month-old), and postpubertal (7-month-old) dog testes. Expression of protein gene product 9.5 (PGP9.5), deleted in azoospermia-like (DAZL), synaptonemal complex protein (SCP3), tyrosine-protein kinase Kit (C-kit), and acrosin was confirmed by immunohistochemical analysis. PGP9.5 and DAZL were detected in spermatogonia and co-localized near the basement membrane of seminiferous tubules. Some SCP3-positive cells expressed PGP9.5 but not C-kit, and most of these cells were located near the basement membrane. C-kit is a marker of differentiated spermatogenic cells. In addition, acrosin was detected in C-kit-positive spematocytes and mature spermatozoa, whereas C-kit was detected in Sertoli cells in all stages of canine testis development. We suggest that male germ cell markers detected in other species are conserved in canines. PGP9.5, DAZL, SCP3, and acrosin expressions were conserved among various species, but C-kit expression varied. This study might facilitate the identification of stage-specific canine germ cell markers and cellular mechanisms of spermatogenesis.