GAPDH and cryptorchidism: With all samples producing a clear signal for GAPDH mRNA, which acted as a housekeeping gene control, the PCR and Western blotting results suggested that ZO-1 and occludin mRNA and protein levels were both significantly down-regulated in cryptorchidism compared to those in the control (testis) (p < 0.01) (Figure 1B,C).