Developmental expression and function of DKKL1/Dkkl1 in humans and mice

BACKGROUND Experiments were designed to identify the developmental expression and function of the Dickkopf-Like1 (DKKL1/Dkkl1) gene in humans and mice. METHODS Mouse testes cDNA samples were collected at multiple postnatal times (days 4, 9, 18, 35, and 54, as well as at 6 months) and hybridized to Affymetrix mouse whole genome Genechips. To further characterize the homologous gene DKKL1 in human beings, the expression profiles between human adult testis and foetal testis were compared using Affymetrix human Genechips. The characteristics of DKKL1/Dkkl1 were analysed using various cellular and molecular biotechnologies. RESULTS The expression of Dkkl1 was not detected in mouse testes on days 4 or 9, but was present on days 18, 35, and 54, as well as at 6 months, which was confirmed by RT-PCR and Western blot results. Examination of the tissue distribution of Dkkl1 demonstrated that while Dkkl1 mRNA was abundantly expressed in testes, little to no expression of Dkkl1 was observed in the epididymis or other tissues. In an in vitro fertilization assay, a Dkkl1 antibody was found to significantly reduce fertilization. Human Genechips results showed that the hybridization signal intensity of DKKL1 was 405.56-fold higher in adult testis than in foetal testis. RT-PCR analysis of multiple human tissues indicated that DKKL1 mRNA was exclusively expressed in the testis. Western blot analysis also demonstrated that DKKL1 was mainly expressed in human testis with a molecular weight of approximately 34 kDa. Additionally, immunohistochemical staining showed that the DKKL1 protein was predominantly located in spermatocytes and round spermatids in human testes. An examination of the expression levels of DKKL1 in infertile male patients revealed that while no DKKL1 appeared in the testes of patients with Sertoli cell only syndrome (SCOS) or cryptorchidism, DKKL1 was observed with variable expression in patients with spermatogenic arrest. CONCLUSIONS These results, together with previous studies, suggest that DKKL1/Dkkl1 may play an important role in testicular development and spermatogenesis and may be an important factor in male infertility.