Biomedical subjects

Masaru Nonaka

Publications and source records attributed to Masaru Nonaka.

26 records · Page 2Linked to original sources

PubMed2003

Origin of mannose-binding lectin-associated serine protease (MASP)-1 and MASP-3 involved in the lectin complement pathway traced back to the invertebrate, amphioxus.

Mannose-binding lectin-associated serine proteases (MASPs) are involved in complement activation through the lectin pathway. To elucidate the phylogenetic origin of MASP and a primordial complement system, we cloned two MASP cDNAs from amphioxus (Branchiostoma belcheri) of the cephalochordates, considered to be the closest relative of vertebrates. The two sequences, orthologues of mammalian MASP-1 and MASP-3, were produced by alternative processing of RNA from a single gene consisting of a common H chain-encoding region and two L chain-encoding regions, a structure which is similar to that of the human MASP1/3 gene. We also isolated two MASP genes from the ascidian Halocynthia roretzi (urochordates) and found that each of them consists simply of an H chain-encoding region and a single L chain-encoding region. The difference in structure between the ascidian MASP genes and the amphioxus/mammalian MASP genes suggests that a prototype gene was converted to the MASP1/3-type gene possessing two L chain-encoding regions at an early stage of evolution before the divergence of amphioxus. This conclusion is supported by the presence of MASP-1 and MASP-3 homologues in almost all vertebrates, as demonstrated by the cloning of novel cDNA sequences representing lamprey (cyclostomes) MASP-1 and Xenopus MASP-3. The ancient origin of MASP-1 and MASP-3 suggests that they have crucial functions common to all species which emerged after cephalochordates.

Amino Acid Sequence↗

PubMed2003

Hemocytes of Ciona intestinalis express multiple genes involved in innate immune host defense.

Ascidians, which are classified as urochordata, appear to employ a primitive system of host defense that is considered to be a prototype of vertebrate innate immunity. We performed a cDNA/EST study to identify the genes expressed in the hemocytes of Ciona intestinalis. We obtained 3357 one-path reads that were then grouped into 1889 independent clusters. Although two thirds of the clusters could not be assigned to any particular gene, the remaining 530 clusters had significant homology to genes with known function. Of these, 62 clusters appeared to be related to host defense mechanisms. These include transcripts whose products are probably involved in cytotoxicity, detoxification, inflammation, and apoptosis. As expected, elements of acquired immunity were not detected. Thus, Ciona hemocytes appear to express a number of host defense-related genes involved in innate immune mechanisms.

Animals↗

PubMed2003

Two highly divergent ancient allelic lineages of the transporter associated with antigen processing (TAP) gene in Xenopus: further evidence for co-evolution among MHC class I region genes.

In the frog Xenopus, MHC class I antigen presentation and processing genes (the immunoproteasome LMP2 and LMP7 and the transporter TAP1 and TAP2) seem to be closely linked in a primordial organization. Two distinct lineages of class Ia and LMP7 loci were previously identified, thus strongly suggesting co-evolution among 'class I region' genes. We now show that the Xenopus MHC 'class I region' lies between class II and class III genes and we have isolated two distinct alleles at both the TAP1 and TAP2 loci. The alleles at each locus are remarkably divergent from each other and phylogenetic tree analysis revealed in both cases that they diverged from each other 60-100 million years ago (MYA). For lineage-frequency and linkage analysis, 25 wild-caught X. laevis and 16 X. tropicalis were examined. The two lineages were present in different frequencies for X. laevis and X. tropicalis. Nevertheless, in all cases, the LMP7, TAP1, and TAP2 lineages were found in a set comprising one of the two lineages. Furthermore, like the LMP7 lineages, the TAP lineages were detected in most Xenopus species that diverged from a common ancestor 80-100 MYA, suggesting that the 'class I region' biallelic lineages are under balancing selection.

Alleles↗

PubMed2002

The draft genome of Ciona intestinalis: insights into chordate and vertebrate origins.

The first chordates appear in the fossil record at the time of the Cambrian explosion, nearly 550 million years ago. The modern ascidian tadpole represents a plausible approximation to these ancestral chordates. To illuminate the origins of chordate and vertebrates, we generated a draft of the protein-coding portion of the genome of the most studied ascidian, Ciona intestinalis. The Ciona genome contains approximately 16,000 protein-coding genes, similar to the number in other invertebrates, but only half that found in vertebrates. Vertebrate gene families are typically found in simplified form in Ciona, suggesting that ascidians contain the basic ancestral complement of genes involved in cell signaling and development. The ascidian genome has also acquired a number of lineage-specific innovations, including a group of genes engaged in cellulose metabolism that are related to those in bacteria and fungi.

Alleles↗

PubMed2002

Nucleotide sequence of the MHC class I genomic region of a teleost, the medaka (Oryzias latipes).

Teleost orthologs of the human major histocompatibility complex (MHC)-encoded genes show a dispersed distribution over several chromosomal loci. However, some of them, including the MHC class I alpha chain genes, are tightly linked to each other, forming the teleost MHC class I region. To elucidate the evolution of vertebrate MHC, we have determined the complete nucleotide sequences of two bacterial artificial chromosome (BAC) clones, encompassing the MHC class I region of the inbred Hd-rR strain of the medaka (Oryzias latipes). The 425862 bp nucleotide sequence predicted 20 possibly expressed genes and three pseudogenes. Except for one gene, CIZ, whose human ortholog is located at 12p13.31, all identified genes were orthologs or closely related relatives of the human MHC-encoded genes. Two classical class I alpha chain genes and the six other genes directly involved in class I antigen presentation formed an uninterrupted cluster. Comparison of the MHC class I region genes among three teleost species, the medaka, zebrafish and pufferfish, indicated that the content, but not the order or transcriptional orientation, of the genes is highly conserved. These results suggest that a strong selective pressure has conserved the linkage of certain MHC genes during vertebrate evolution, despite recurrent genetic rearrangements.

Amino Acid Sequence↗

PubMed2002

C6-like and C3-like molecules from the cephalochordate, amphioxus, suggest a cytolytic complement system in invertebrates.

The mammalian immune system has cytotoxic mechanisms, both cellular and humoral, that destroy the membrane integrity of target cells. The main effector molecules of these cytolytic mechanisms-perforin, used by killer lymphocytes, and the membrane attack complex (MAC) components of the complement system-share a unique module called the MAC/perforin module. Until now, both immunological cytotoxicity and the MAC/perforin module have been reported only in jawed vertebrates. Here, we report the identification of a protein containing the MAC/perforin module from the invertebrate cephalochordate, amphioxus ( Branchiostoma belcheri), using expressed sequence tag (EST) analysis of the notochord. The deduced amino acid sequence of this molecule is most similar to the primary structure of human complement component C6 and is designated AmphiC6. AmphiC6 shares a unique modular structure, including the MAC/perforin module, with human C6 and other MAC components. Another EST clone predicts the presence of a thioester-containing protein with the closest structural similarity to vertebrate C3 (therefore designated AmphiC3). AmphiC3 retains most of the functionally important residues of vertebrate C3 and is shown by phylogenetic analysis to be derived directly from the common ancestor of vertebrate C3, C4, and C5. Only opsonic activity has been assigned to the invertebrate complement system until now. Therefore, this is the first molecular evidence for complement-mediated immunological cytotoxicity in invertebrates.

Amino Acid Sequence↗

PubMed2002

Conservation of the modular structure of complement factor I through vertebrate evolution.

Mammalian complement factor I plays pivotal roles in the regulation of complement activation and generation of important biological activities from C3. The evolutionary origin of factor I has been unclear except with regard to the molecular cloning of factor I from amphibian Xenopus. Here, we report the identification and characterization of factor I cDNA from the liver of the banded houndshark. The deduced amino acid sequence of shark factor I showed a modular organization that was completely identical to that of mammalian factor I, suggesting the functional conservation of factor I throughout vertebrate evolution. Functionally important amino acid residues such as the basic residues at the processing site and the residues at the active site of the serine protease domain are conserved. Repeated sequences composed of 16 amino acids were inserted at a site between the leader peptide and the factor I/membrane attacking complex module in the shark factor I. This repeat is missing from mammalian and amphibian factor I, and the biological significance of the sequence, if any, is not clear at the moment. There was only one copy of the shark factor I gene, and Northern blotting analysis showed that the shark factor I gene was expressed only in the liver among several organs tested. While the lack of functional data does not exclude the possibility that factor I could have a different function, all these facts, together with the earlier reported data suggest the existence of a well developed complement system in cartilaginous fish.

Amino Acid Sequence↗

PubMed2001

Evolution of the initiating enzymes of the complement system.

Analysis of the human MASP-1/3 gene, which encodes two proteases of the lectin-triggered complement cascade, has revealed alternatively used serine-protease-encoding regions for the gene's two protein products. Phylogenetic studies indicate that one arose by retrotransposition early in vertebrate evolution, supporting the idea that the lectin branch of the complement cascade arose earlier than the 'classical' pathway.

Alternative Splicing↗