Expression pattern of Dkkl1 in mice. A: Mouse Dkkl1 mRNA was not expressed in mouse testis on days 4 and 9 and was weakly expressed on day 18. The expression increased gradually from day 18 to 54 and remained stable after day 54. β-actin was used as an internal loading control. B: The expression pattern of Dkkl1 mRNA in 12 different mouse tissues is shown. Except for a trace amount of Dkkl1 mRNA in the epididymis, expression of Dkkl1 was found only in testis. GAPDH was used as an internal control. C: Representative Western blot analyses of protein from samples obtained from testes at postnatal days 4, 9, 18, 35, and 54, as well as at 6 months. The expression of GAPDH was used as an internal standard for normalization. The protein level of Dkkl1 increased during testicular development, which is consistent with the expression of Dkkl1 mRNA. The size of the Dkkl1 protein was approximately 34 kDa. D: In each of three replicate analyses, Western blot results were quantified, and the results were expressed as the ratio of Dkkl1/GAPDH. The bars represent the mean ± SD of the data for each age, and the bars marked with asterisks showed statistically significant differences (p < 0.05).