Figure 3: Expression profiles of NODAL protein in OA and SCO testis. ( a ): Immunocytochemical staining showed that NODAL was expressed in VASA-positive cells in OA testis. No specific staining was seen in Sertoli cells and interstitium. There was no specific VASA and NODAL staining in SCO testis. There was nonspecific staining of the enclosed tubules and interstitium in both OA and SCO testis, which could also be seen in negative control slides ( b and c ). "*" indicated the basement membrane, while "^" indicated the spermatogonia. ( b and c ): Negative control of immunocytochemistry of the human testes. Notes - OA: obstructive azoospermia, SCO: Sertoli cell-only syndrome. Scale bars = 50 μm.