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Dechorionation of Medaka Embryos and Cell Transplantation for the Generation of Chimeras
Published on: December 22, 2010
Molecular cloning and linkage analysis of complement C3 and C4 genes of the Japanese medaka fish
1Department of Biochemistry, Nagoya City University Medical School, Nagoya, Japan.
Insights
The study analyzed Japanese medaka fish complement genes C3 and C4, revealing structural similarities to mammals but functional divergence in C3. This suggests the major histocompatibility complex (MHC) class III region evolved in tetrapods.
Area of Science:
- Evolutionary biology
- Immunogenetics
- Comparative genomics
Background:
- Complement components C3 and C4, crucial for innate immunity, are thioester-containing proteins thought to originate from gene duplication.
- Mammalian C4 genes are located within the major histocompatibility complex (MHC) class III region, near C2 and B genes.
Purpose of the Study:
- To investigate the evolutionary history of the complement system and MHC.
- To determine the primary structures and gene organization of C3 and C4 in the teleost Japanese medaka (Oryzias latipes).
Main Methods:
- Isolation and analysis of cDNA clones from a Japanese medaka liver library.
- Determination of complete primary structures of two C3 genes (Orla C3-1, Orla C3-2) and one C4 gene (Orla C4).
- Gene mapping to analyze linkage relationships.
Main Results:
- Orla C3-1, Orla C3-2, and Orla C4 share basic structural features with mammalian counterparts, including thioester and activation sites.
- A key catalytic residue (His) is replaced by Ala in Orla C3-2, suggesting functional differentiation between the two medaka C3 genes.
- Medaka C3 genes are closely linked, indicating local duplication, while the C4 gene is on a different linkage group, unlinked to other MHC loci.
Conclusions:
- The Japanese medaka complement genes provide insights into the evolution of C3 and C4.
- Functional divergence of C3 genes may have occurred early in vertebrate evolution.
- The MHC class III complement region likely established in tetrapods or was lost in teleosts, as evidenced by gene linkage patterns.
Abstract:
The thioester-containing complement components, C3 and C4, are believed to have arisen by gene duplication from a common ancestor, and the mammalian C4 gene resides in the vicinity of the C2 and B genes within the major histocompatibility complex (MHC) class III region. To analyze the evolution of both the complement system and the MHC, we determined the complete primary structures of two C3 genes, termed Orla C3-1 and Orla C3-2, and one C4 gene, termed Orla C4, of a teleost, Japanese medaka fish (Oryzias latipes), by analyzing cDNA clones isolated from a liver library constructed using the inbred AA2 strain. The deduced basic structures of Orla C3-1, C3-2, and C4, such as the subunit chain structure, the thioester site, and the proteolytic activation site, are similar to their mammalian counterparts. However, the catalytic His residue which greatly increases the rate of thioester reaction, is replaced by Ala in Orla C3-2, implying functional differentiation between two C3 molecules. Mapping analysis revealed a close linkage between the C3-1 and C3-2 genes, indicating that they arose by a local duplication rather than by a genome-wide tetraploidization. The C4 gene belongs to a different linkage group, and no linkage was observed among the C3, C4, Bf/C2, MHC class I, and MHC class II loci. These results suggest that the MHC class III complement region was established in the tetrapod lineage, or lost in the teleost lineage.
