Naoki Osada

Extensive expansion and diversification of the chemokine gene family in zebrafish: Identification of a novel chemokine subfamily CX

BackgroundThe chemokine family plays important roles in cell migration and activation. In humans, at least 44 members are known. Based on the arrangement of the four conserved cysteine residues, chemokines are now classified into four subfamilies, CXC, CC, XC and CX3C. Given that zebrafish is an important experimental model and teleost fishes constitute an evolutionarily diverse group that forms half the vertebrate species, it would be useful to compare the zebrafish chemokine system with those of mammals. Prior to this study, however, only incomplete lists of the zebrafish chemokine genes were reported.ResultsWe systematically searched chemokine genes in the zebrafish genome and EST databases, and identified more than 100 chemokine genes. These genes were CXC, CC and XC subfamily members, while no CX3C gene was identified. We also searched chemokine genes in pufferfish fugu and Tetraodon, and found only 18 chemokine genes in each species. The majority of the identified chemokine genes are unique to zebrafish or teleost fishes. However, several groups of chemokines are moderately similar to human chemokines, and some chemokines are orthologous to human homeostatic chemokines CXCL12 and CXCL14. Zebrafish also possesses a novel species-specific subfamily consisting of five members, which we term the CX subfamily. The CX chemokines lack one of the two N-terminus conserved cysteine residues but retain the third and the fourth ones. (Note that the XC subfamily only retains the second and fourth of the signature cysteines residues.) Phylogenetic analysis and genome organization of the chemokine genes showed that successive tandem duplication events generated the CX genes from the CC subfamily. Recombinant CXL-chr24a, one of the CX subfamily members on chromosome 24, showed marked chemotactic activity for carp leukocytes. The mRNA was expressed mainly during a certain period of the embryogenesis, suggesting its role in the zebrafish development.ConclusionThe phylogenic and genomic organization analyses suggest that a substantial number of chemokine genes in zebrafish were generated by zebrafish-specific tandem duplication events. During such duplications, a novel chemokine subfamily termed CX was generated in zebrafish. Only two human chemokines CXCL12 and CXCL14 have the orthologous chemokines in zebrafish. The diversification observed in the numbers and sequences of chemokines in the fish may reflect the adaptation of the individual species to their respective biological environment.

Duplication and Gene Conversion in the Drosophila melanogaster Genome

Using the genomic sequences of Drosophila melanogaster subgroup, the pattern of gene duplications was investigated with special attention to interlocus gene conversion. Our fine-scale analysis with careful visual inspections enabled accurate identification of a number of duplicated blocks (genomic regions). The orthologous parts of those duplicated blocks were also identified in the D. simulans and D. sechellia genomes, by which we were able to clearly classify the duplicated blocks into post- and pre-speciation blocks. We found 31 post-speciation duplicated genes, from which the rate of gene duplication (from one copy to two copies) is estimated to be 1.0×10−9 per single-copy gene per year. The role of interlocus gene conversion was observed in several respects in our data: (1) synonymous divergence between a duplicated pair is overall very low. Consequently, the gene duplication rate would be seriously overestimated by counting duplicated genes with low divergence; (2) the sizes of young duplicated blocks are generally large. We postulate that the degeneration of gene conversion around the edges could explain the shrinkage of “identifiable” duplicated regions; and (3) elevated paralogous divergence is observed around the edges in many duplicated blocks, supporting our gene conversion–degeneration model. Our analysis demonstrated that gene conversion between duplicated regions is a common and genome-wide phenomenon in the Drosophila genomes, and that its role should be especially significant in the early stages of duplicated genes. Based on a population genetic prediction, we applied a new genome-scan method to test for signatures of selection for neofunctionalization and found a strong signature in a pair of transporter genes.

Ancient genome‐wide admixture extends beyond the current hybrid zone between Macaca fascicularis and M. mulatta

Macaca fascicularis and Macaca mulatta are two of the most commonly used laboratory macaques, yet their genetic differences at a genome‐wide level remain unclear. We analysed the multilocus DNA sequence data of 54 autosomal loci obtained from M. fascicularis samples from three different geographic origins and M. mulatta samples of Burmese origin. M. fascicularis shows high nucleotide diversity, four to five times higher than humans, and a strong geographic population structure between Indonesian‐Malaysian and Philippine macaques. The pattern of divergence and polymorphism between M. fascicularis and M. mulatta shows a footprint of genetic exchange not only within their current hybrid zone but also across a wider range for more than 1 million years. However, genetic admixture may not be a random event in the genome. Whereas randomly selected genic and intergenic regions have the same evolutionary dynamics between the species, some cytochrome oxidase P450 (CYP) genes (major chemical metabolizing genes and potential target genes for local adaptation) have a significantly larger species divergence than other genes. By surveying CYP3A5 gene sequences of more than a hundred macaques, we identified three nonsynonymous single nucleotide polymorphisms that were highly differentiated between the macaques. The mosaic pattern of species divergence in the genomes may be a consequence of genetic differentiation under ecological adaptation and may be a salient feature in the genomes of nascent species under parapatry.

Large-scale analysis of Macaca fascicularis transcripts and inference of genetic divergence between M. fascicularis and M. mulatta

BackgroundCynomolgus macaques (Macaca fascicularis) are widely used as experimental animals in biomedical research and are closely related to other laboratory macaques, such as rhesus macaques (M. mulatta). We isolated 85,721 clones and determined 9407 full-insert sequences from cynomolgus monkey brain, testis, and liver. These sequences were annotated based on homology to human genes and stored in a database, QFbase http://genebank.nibio.go.jp/qfbase/.ResultsWe found that 1024 transcripts did not represent any public human cDNA sequence and examined their expression using M. fascicularis oligonucleotide microarrays. Significant expression was detected for 544 (51%) of the unidentified transcripts. Moreover, we identified 226 genes containing exon alterations in the untranslated regions of the macaque transcripts, despite the highly conserved structure of the coding regions. Considering the polymorphism in the common ancestor of cynomolgus and rhesus macaques and the rate of PCR errors, the divergence time between the two species was estimated to be around 0.9 million years ago.ConclusionTranscript data from Old World monkeys provide a means not only to determine the evolutionary difference between human and non-human primates but also to unveil hidden transcripts in the human genome. Increasing the genomic resources and information of macaque monkeys will greatly contribute to the development of evolutionary biology and biomedical sciences.

IL-10 Is a Negative Regulatory Factor of CAWS-Vasculitis in CBA/J Mice as Assessed by Comparison with Bruton’s Tyrosine Kinase-Deficient CBA/N Mice

Candida albicans water-soluble fraction (CAWS), a mannoprotein-β-glucan complex obtained from the culture supernatant of C. albicans NBRC1385, exhibits vasculitis-inducing activity (CAWS-vasculitis) in mice. The sensitivity to CAWS-vasculitis varies greatly among mouse strains. This study examined the factors contributing to or inhibiting CAWS-vasculitis using CAWS-vasculitis-resistant CBA/J mice and Bruton’s tyrosine kinase-deficient CBA/N mice, which is a CAWS-vasculitis-sensitive strain that has the same origin as CBA/J mice. After stimulation with various kinds of pathogen-associated molecular patterns, the production of inflammatory cytokines IL-6 and IFN-γ was induced in CBA/N mice, whereas that of immunosuppressive IL-10 was induced in CAWS-vasculitis-resistant CBA/J mice. Furthermore, the production of tissue inhibitor of metalloproteinase 1, an endogenous matrix metalloproteinase inhibitor, was observed in CBA/J mice. The results strongly suggest that the difference in the production of these cytokines is closely linked to the development of CAWS-vasculitis.

Quantifying dominance and deleterious effect on human disease genes

Human genes responsible for inherited diseases are important for the understanding of human disease. We investigated the degree of polymorphism and divergence in the human disease genes to elucidate the effect of natural selection on human disease genes. In particular, the effect of disease dominance was incorporated into the analysis. Both dominant disease genes (DDG) and recessive disease genes (RDG) had a higher mutation rate per site and encoded longer proteins than the nondisease genes, which exposed the disease genes to a faster flux of new mutations. Using an unbiased polymorphism dataset, we found that, proportionally, RDG harbor more nonsynonymous polymorphisms compared with DDG. We estimated the selection intensity on the disease genes using polymorphism and divergence data and determined whether the different patterns of polymorphism and divergence between DDG and RDG could be explained by the difference in only dominance. Even after the dominance effect was considered, the selection intensity on RDG was significantly different from DDG, suggesting that the deleterious effect of the dominant and recessive disease mutations are fundamentally different.

Collection of Macaca fascicularis cDNAs derived from bone marrow, kidney, liver, pancreas, spleen, and thymus.

BackgroundConsolidating transcriptome data of non-human primates is essential to annotate primate genome sequences, and will facilitate research using non-human primates in the genomic era. Macaca fascicularis is a macaque monkey that is commonly used for biomedical and ecological research.FindingsWe constructed cDNA libraries of Macaca fascicularis, derived from tissues obtained from bone marrow, liver, pancreas, spleen, and thymus of a young male, and kidney of a young female. In total, 5-end sequences of 56,856 clones were determined. Including the previously established cDNA libraries from brain and testis, we have isolated 112,587 cDNAs of Macaca fascicularis, which correspond to 56% of the curated human reference genes.ConclusionThese sequences were deposited in the public sequence database as well as in-house macaque genome database http://genebank.nibio.go.jp/qfbase/. These data will become valuable resources for identifying functional parts of the genome of macaque monkeys in future studies.

Development of an integrative database with 499 novel microsatellite markers for Macaca fascicularis

BackgroundCynomolgus macaques (Macaca fascicularis) are a valuable resource for linkage studies of genetic disorders, but their microsatellite markers are not sufficient. In genetic studies, a prerequisite for mapping genes is development of a genome-wide set of microsatellite markers in target organisms. A whole genome sequence and its annotation also facilitate identification of markers for causative mutations. The aim of this study is to establish hundreds of microsatellite markers and to develop an integrative cynomolgus macaque genome database with a variety of datasets including marker and gene information that will be useful for further genetic analyses in this species.ResultsWe investigated the level of polymorphisms in cynomolgus monkeys for 671 microsatellite markers that are covered by our established Bacterial Artificial Chromosome (BAC) clones. Four hundred and ninety-nine (74.4%) of the markers were found to be polymorphic using standard PCR analysis. The average number of alleles and average expected heterozygosity at these polymorphic loci in ten cynomolgus macaques were 8.20 and 0.75, respectively.ConclusionBAC clones and novel microsatellite markers were assigned to the rhesus genome sequence and linked with our cynomolgus macaque cDNA database (QFbase). Our novel microsatellite marker set and genomic database will be valuable integrative resources in analyzing genetic disorders in cynomolgus macaques.

Multiple duplication of the bucentaur gene family, which recruits the APE-like domain of retrotransposon : Identification of a novel homolog and distinct cellular expression

The p97bcnt/cfdp2 is a ruminant-specific gene created by a combination of gene duplication of ancestral bcnt (bucentaur) or cfdp1 (craniofacial developmental protein 1), bcnt/cfdp1, and the insertion of a retrotransposable element-1 (RTE). As a result, p97Bcnt recruits the whole apurinic/apyrimidinic endonuclease (APE)-like domain of RTE in the middle of the molecule (RTE domain) as a region encoded by an exon. In addition, p97Bcnt contains two intramolecular repeats (IRs) of 40 amino acids each in the C-terminal region, whereas Bcnt/Cfdp1 contains one IR. We have identified an additional bovine homolog with a structure highly similar to p97Bcnt, designated p97Bcnt2, which contains three IRs. p97bcnt2 is located in tandem with bcnt/cfdp1 and p97bcnt within a 177-kb range on bovine chromosome 18, a syntenic region of human chromosome 16. The gene product is expressed as a protein with an apparent molecular mass of 102 kDa. The phylogenetic tree strongly suggests that p97bcnt-2 forms a third clade of the bcnt family and that the first duplication of the IR unit occurred prior to the divergence of p97bcnt and p97bcnt-2. To address the question of whether these bcnt members have distinct functions, we first examined the expression and localization of the p97Bcnt family members. p97Bcnt is substantially expressed in many tissues involved in responses to external and internal stress. In the testis, p97Bcnt localizes preferentially in the nuclei of spermatozoa, while Bcnt/Cfdp1 localizes predominantly in the cytosol of Leydig cells and some spermatogenic cells, implying that at least these two molecules of the Bcnt family play different functional roles. These results provide evidence for the direct contribution of RTE to gene diversity to form gene families that may support cellular function.