Spatial Expression of Osteopontin in Testis, Epididymis and Spermatozoa in Dromedary Camel

The aim of this study is to clarify the function of osteopontin (OPN) through its expression and localisation in male testis, epididymis and sperm cell of dromedary camel during rutting season. Testis and epididymis parts (caput, corpus and cauda) specimens were obtained from 8 mature male camels and semen was collected from 4 another fertile camels for sperms. OPN mRNA expression and its location was analysed using quantitative real-time polymerase chain reaction (qRT-PCR) and immunohistochemistry (IHC) techniques, respectively. OPN mRNA expression was significantly (P < 0.05) higher in the cauda of epididymis than other epididymal parts and testis. Immunolocalisation revealed high immunoreaction intensity in the elongated spermatids in seminiferous tubules and Leydig cells in interstitial tissue. However, a faint immunostaining was seen in spermatogonia and Sertoli cells. Along the epididymis tract, intense immunoreactivity of OPN was localised in the cytoplasm of the epithelial cells with high concentration in the apical region nearby lumen and the acrosomal part of the cauda epididymal sperms. Immunofluorescence and immunochromogenic staining of OPN was detected on the acrosomal cap and neck of epididymal sperms. These findings suggested that OPN might play an important role in the sperm protection, migration and fertilisation in dromedary camels.