Characterization of a novel cell-surface protein expressed on human sperm.
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.


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.
Yang
Ruey-Bing
RB
Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan.
Au
Heng-Kien
HK
Tzeng
Chii-Ruey
CR
Tsai
Ming-Tzu
MT
Wu
Ping
P
Wu
Yu-Chih
YC
Ling
Thai-Yen
TY
Huang
Yen-Hua
YH
D000177:Acrosome / Q000378:metabolism; D020101:Acrosome Reaction; D020816:Amino Acid Motifs; D001665:Binding Sites; D015153:Blotting, Western; D002874:Chromosome Mapping; D002879:Chromosomes, Human, Pair 10; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D006801:Humans; D008297:Male; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D050705:Receptors, Guanylate Cyclase-Coupled / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D017422:Sequence Analysis, DNA; D013075:Sperm Capacitation; D013084:Sperm-Ovum Interactions; D013094:Spermatozoa / Q000378:metabolism*; D013737:Testis / Q000378:metabolism
D008565:Membrane Proteins; D012333:RNA, Messenger; C547507:hGC-G protein, human; D050705:Receptors, Guanylate Cyclase-Coupled