Figure 4: Expression profiles of NODAL's receptors in OA and SCO testis. (a): Immunohistochemical staining showed that ALK4, ALK7, and ACTR-IIB were detected in GATA4-positive Sertoli cells in OA testis. (a'): Negative control of immunocytochemistry of the OA testes, displaying nonspecific staining. (b): Immunohistochemical staining displayed that ALK4, ALK7, and ACTR-IIB were expressed in GATA4-positive Sertoli cells in SCO testis. No specific staining was seen in other cells. (b'): Negative control of immunohistochemistry of the OA testes without primary antibody. Scale bars = 50 ƒÊm. OA: obstructive azoospermia; SCO: Sertoli cell-only syndrome.