Polymorphic expression of DAZ proteins in the human testis

Abstract

Background: DAZ is a male infertility gene located at the AZFc region of the Y chromosome. There are four copies of the DAZ gene that share a strong homology but are not identical to one another. In the present study, we carried out cDNA cloning and immunoblot analyses to determine whether all of the DAZ genes are actively expressed in the human testis. Methods: AZFc deletion was detected by sequence-tagged site polymerase chain reaction (PCR) of genomic DNA isolated from blood samples. DAZ cDNAs were cloned with RT-PCR followed by sequence analysis. The expression of DAZ proteins in human testis was determined by immunoblot and compared with DAZ cDNA expression. Results: Immunoblot analysis revealed four DAZ protein bands in testis samples that showed no deletions in the AZFc region. No specific bands were observed in samples from AZFc deletion patients. Testis samples from individuals with the partial AZFc deletion, gr/gr, showed two DAZ-specific bands. Interestingly, the sizes of DAZ-specific bands varied among individuals. Analysis of DAZ transcripts in testis samples revealed that the DAZ proteins were translated from the largest of the multiple transcripts originating from each single DAZ gene. Conclusions: All four DAZ genes are expressed in the human testis, and their products are highly polymorphic among men.