Localization and expression characteristics of DKKL1 protein in the testis of fertile and infertile patients by immunohistochemistry assay. A: DKKL1 protein was predominantly located in the spermatocytes and round spermatids in fertile testes. B: No staining was observed in tissue sections when the DKKL1 antibody was replaced by buffer containing 1% BSA. C: In the spermatogenic arrest testis, the layers of spermatogenesis cells decreased and a number of vacuoles were observed in the lumen. Reduced DKKL1 protein signal was detected in spermatocytes and round spermatids. D: In the SCOS or cryptorchidism testis, the basal membrane of the seminiferous tubules was thickened; only Sertoli cells and spermatogonial cells were found in the seminiferous epithelia. No DKKL1 protein signal was detected. Scale bar = 25 μm.