Hum. Reprod. Advance Access published online on October 14, 2009
Human Reproduction, doi:10.1093/humrep/dep359
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Characterization of a novel cell-surface protein expressed on human sperm
1 Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan 2 Institute of Pharmacology, School of Medicine, National Yang-Ming University, Taipei, Taiwan 3 Department of Obstetrics and Gynecology, School of Medicine, Taipei, Taiwan 4 Center for Reproductive Medicine, Taipei Medical University and the Hospital, Taipei, Taiwan 5 Department of Biochemistry, College of Medicine, Taipei Medical University, Taipei, Taiwan 6 Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei, Taiwan 7 Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan 8 Institute of Pharmacology, National Taiwan University, Taipei, Taiwan
9 Correspondence address. Tel: +886-2-27361661-3150; Fax: +886-2-2735-6689; E-mail: rita1204{at}tmu.edu.tw
BACKGROUND: Precise sperm–oocyte interaction is a critical event for successful fertilization. However, the identity of molecules involved in this process in humans remains largely unknown. This report describes the identification and characterization of a novel cell-surface protein and its potential role in human sperm–oocyte interaction.
METHODS AND RESULTS: We previously identified an orphan guanylyl cyclase receptor (mouse GC-G) highly enriched in mouse testis and involved in sperm activation. By using a comparative genomic approach, we found the homologue gene in human (hGC-G) composed of 21 exons, spanning a minimum of 48 kb on chromosome 10q25. Real-time RT–PCR analysis revealed hGC-G mRNA selectively expressed in testis but with low or no expression in all other tissues examined. Compared with mGC-G, the hGC-G transcript contains three 1-bp deletions and two in-frame termination codons, which results in a short putative receptor-like polypeptide. Western blot analysis with an anti-hGC-G-specific antibody confirmed the protein expression of hGC-G in human sperm lysate. Flow cytometry and confocal immunofluorescence analysis demonstrated the localization of hGC-G protein on the acrosome cap and equatorial segment of mature human sperm. In addition, an integrin-binding Arg-Gly-Asp (RGD) motif was found in the extracellular domain of hGC-G. Pre-incubation of the hGC-G RGD peptide with zona pellucida-free oocytes greatly decreased the binding of human sperm to hamster oocytes, which suggests a role for hGC-G role in sperm–oocyte interaction.
CONCLUSIONS: hGC-G is a novel surface protein on human sperm and potentially mediates sperm–oocyte interaction through its RGD-containing motif.
Key words: cell-surface protein/human sperm/RGD motif/integrin/gamete interaction
These authors contributed equally to this work. Submitted on April 28, 2009; resubmitted on August 11, 2009; accepted on September 10, 2009.