Structure and the evolutionary implication of the triplicated complement factor B genes of a urochordate ascidian, Ciona intestinalis

Fumiko Y. Yoshizaki, Shuntaro Ikawa, Masanobu Satake, Nori Satoh, Masaru Nonaka

Research output: Contribution to journalArticlepeer-review

34 Citations (Scopus)

Abstract

To elucidate the evolution of the complement system and MHC class III region, we analyzed the complement factor B (Bf) genes of a urochordate ascidian, Ciona intestinalis. Three different cDNA species, termed CiBf-1, CiBf-2 and CiBf-3, were identified. The deduced amino-acid sequences all contained the usual domains of vertebrate Bf and, in addition, three extra domains at the N-terminus. Furthermore, the serine protease domain of these CiBfs shared unique features with vertebrate complement components C1r/s and mannose-binding lectin-associated serine protease (MASP)-2/3, the absence of the disulfide bond designated histidine loop, and the usage of the AGY codon for the catalytic serine residue. These results indicate that complement genes have evolved through extensive exon shuffling events in the early stage of chordate evolution. Overall deduced amino-acid identity between CiBf-1 and -2 was 88%, whereas CiBf-3 showed 49% identity to both CiBf-1 and CiBf-2. These three CiBf genes were located within an approximately 50-kb genomic region, and exons 3 and 5 of all the three Bf genes showed an extremely high degree of nucleotide identity, indicating that the CiBf genes experienced extensive reorganization, such as duplication and gene conversion, since its divergence from the vertebrate Bf/C2 gene. Fluorescent in situ hybridization (FISH) to the chromosomes showed that genetic loci for the CiBfs, CiC3-1 and CiC3-2 genes are present on three different chromosomes, suggesting the possibility that the linkage among the MHC class III complement genes was established in the vertebrate lineage after its divergence from urochordates.

Original languageEnglish
Pages (from-to)930-942
Number of pages13
JournalImmunogenetics
Volume56
Issue number12
DOIs
Publication statusPublished - 2005 Mar

Keywords

  • Ciona intestinalis
  • Complement factor B
  • Exon shuffling
  • Innate immunity
  • Urochordate

ASJC Scopus subject areas

  • Immunology
  • Genetics

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