Hum. Reprod. Advance Access originally published online on April 1, 2008
Human Reproduction 2008 23(6):1280-1289; doi:10.1093/humrep/den099
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Restricted expression of the human DAZ protein in premeiotic germ cells
1 Department of Urology, School of Medicine, National Yang-Ming University, Taipei 11221, Taiwan 2 Division of Urology, Department of Surgery, Taipei Veterans General Hospital, Taipei 11217, Taiwan 3 Institute of Biomedical Sciences, Academia Sinica, 128 Academia Road, Sec. 2, Taipei 11529, Taiwan 4 Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 11490, Taiwan 5 Division of Urology, Department of Surgery, Harbor-UCLA Medical Center, Torrance, CA 90505, USA 6 CIBERER, Hospital Universitario de Canaries, Spain 7 Department of Pathology, Universidad de La Laguna, E-38071 Tenerife, Spain 8 Division of Medical Genetics, Harbor-UCLA Medical Center, Torrance, CA 90505, USA 9 Present address: Century Urology Medical Group, 2080 Century Park East, Suite 1407, Los Angeles, CA 90067, USA
10 Correspondence address. Tel: +886-2-2652-3912; Fax: +886-2-2782-9224; E-mail: pyen{at}ibms.sinica.edu.tw
BACKGROUND: The role of the Y chromosome-encoded Deleted in Azoospermia (DAZ) gene family in spermatogenesis remains unclear. The ability of men without the DAZ gene to produce sperm, as well as the lack of selective pressure on DAZ exon sequences during evolution, casts doubts on its functional significance. Most men have four DAZ genes encoding protein isoforms that differ significantly in size. However, published western blots showed only a single "DAZ" band, raising the possibility that not all four DAZ genes are expressed.
METHODS: RT–PCR, western blotting and immunostaining were used to study the expression of the four DAZ genes and the autosomal DAZL gene in human testes and in tissue culture cells.
RESULTS: RNA transcripts of all four DAZ genes were found in the testis, but at much lower levels than that of the DAZL transcripts. Expression in cultured somatic cells showed that DAZ transcripts encoding multiple DAZ repeats were translated inefficiently. No DAZ proteins could be unambiguously identified on western blots when the testicular samples from three patients without the DAZ genes were used as negative controls. Nonetheless, low levels of DAZ were detected in the cytoplasm of spermatogonia by immunostaining.
CONCLUSIONS: The expression of DAZ proteins in adult human testes is restricted to the spermatogonia and suggests a premeiotic role.
Key words: DAZ/DAZL/male infertility/spermatogenesis
Submitted on September 28, 2007; resubmitted on February 24, 2008; accepted on March 4, 2008.