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Molecular cloning of guinea pig membrane cofactor protein: preferential expression in testis
M Hosokawa1, M Nonaka, N Okada
1Department of Molecular Biology, Nagoya City University School of Medicine, Japan.
Abstract:
Human membrane cofactor protein (MCP) is a widely distributed cell-associated complement-regulatory protein, and recent findings suggest that MCP may be involved in sperm-egg interaction. We have isolated four cDNA clones and one reverse transcriptase-PCR product homologous to human MCP from guinea pig testis. These clones defined five isoform classes generated from a single copy gene by alternative splicing. Reverse transcriptase-PCR revealed that two classes for the clones termed GMP1 and GM2 were predominant. GMP1 consisted of four short consensus repeats (SCRs), regions corresponding to the human serine/threonine/proline-rich C (STP(C)) domain and a human region of unknown significance, a hydrophobic region presumed to be a transmembrane domain, and a cytoplasmic region. Identity with human MCP in the SCR region was 56% at the amino acid level and 71% at the nucleotide level. GM2 had the same structure as GMP1, except that it lacked the fourth SCR, which is presumed to be essential for C3b binding of human MCP. Northern blotting analysis of various tissues revealed a significant level of MCP transcripts in testis. Guinea pig MCP is likely to have only one STP domain that is homologous to human STP(C) and is similar in this respect to human spermatozoa MCP. Gene analysis revealed a single base deletion and a lack of consensus sequences for splicing in the guinea pig regions corresponding to human STP(A) and STP(B), respectively. These results suggest that guinea pig MCP plays a more restricted role in reproduction than does human MCP.
Insights
Guinea pig membrane cofactor protein (MCP) exhibits distinct isoforms, with GMP1 and GM2 being predominant. These findings suggest a more limited reproductive role for guinea pig MCP compared to its human counterpart.
Area of Science:
- Immunology
- Reproductive Biology
- Molecular Biology
Background:
- Membrane cofactor protein (MCP) is a cell-associated complement-regulatory protein.
- Recent research indicates a potential role for MCP in sperm-egg interactions.
Purpose of the Study:
- To investigate the isoforms and structure of membrane cofactor protein (MCP) in guinea pig testis.
- To compare guinea pig MCP with human MCP, particularly regarding its potential role in reproduction.
Main Methods:
- Isolation of cDNA clones and reverse transcriptase-polymerase chain reaction (RT-PCR) from guinea pig testis.
- Northern blotting analysis to determine MCP transcript levels in various tissues.
- Gene analysis to identify structural differences between guinea pig and human MCP.
Main Results:
- Five MCP isoform classes were identified in guinea pigs, with GMP1 and GM2 being predominant.
- GMP1 contains four short consensus repeats (SCRs), a transmembrane domain, and a cytoplasmic region, showing 56% amino acid identity to human MCP.
- GM2 lacks the fourth SCR, crucial for human MCP's C3b binding; guinea pig MCP has one STP domain homologous to human STP(C), unlike human MCP's multiple STP domains.
Conclusions:
- Guinea pig MCP exhibits structural variations, including fewer STP domains, compared to human MCP.
- These differences suggest a more restricted function for guinea pig MCP in reproductive processes.
- MCP's role in reproduction may vary significantly across species.