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Genomic structure and sequence analysis of the valyl-tRNA synthetase gene of the Japanese pufferfish, Fugu rubripes.

The genomic sequence and exon-intron organisation of the valyl-tRNA synthetase gene in the Japanese pufferfish, Fugu rubripes, have been determined. This single-copy Fugu gene spans 8.5 kb, about 2.5 times smaller than that in man (21 kb). It contains 29 exons, with the largest intron being 1008 bp. The predicted polypeptide consists of 1217 amino acids, with a molecular weight of 138 kD and an isoelectric point of 7.27. It shares 40% identity in the overlapping region with its homolog in bacteria, 47% with yeast, and 67% with man. The Fugu gene has an additional N-terminal sequence which shows strong similarity to elongation factory-1gamma, a feature it shares only with the human sequence, but not with any other lower eukaryote or prokaryote studied so far. This N-terminal segment is encoded in the first six exons, suggesting their capture by a translocation through introns. Indeed, the acquisition of extra domains to perform related functions in RNA splicing and translation of polypeptides has already been observed in other aminoacyl-tRNA synthetases. Two cDNA sequences of human valyl-tRNA synthetase have been published, with discrepancies between them. Aided by comparisons with the Fugu gene, three of these discrepancies have been resolved, involving the elucidation of the sequence and positions of two introns. This compact vertebrate genome has demonstrated its value as a tool for the analysis of genes at the genomic level.

Amino Acid Sequence↗

Discovery of a new class of immunoglobulin heavy chain from fugu.

In teleosts, the genomic organization of the immunoglobulin (Ig) heavy (H)-chain locus was thought to follow a typical translocon-type multigene structure; however, recent studies have indicated a variation in the structure and this might be teleost specific. Isotypes of the Ig H-chain, namely IgM, IgD, IgZ and IgT, have been identified. In this study, we report the discovery of a new class of IgH from fugu. This isotype was first identified from the genomic sequence of the fugu IgH locus. This novel IgH gene is composed of two constant (C) domains, a hinge region, and two exons encoding membrane regions. Surprisingly, the new IgH gene is present between the variable (V)H and Cmu regions of the locus. The C domains of the new isotype do not show any significant similarity to mammalian or fish IgH genes. The cloned cDNA from the new isotype has typical Ig H-chain characteristics and is expressed as both secretory and membrane form. Transcript analyses suggest that the new IgH from fugu might only use the joining (J)H segments present in front of the new CH domains and that the usage of DH and JH segments is specific to the isotype expressed. The expression pattern of the gene has been confirmed by in situ hybridization and PCR studies.

Amino Acid Sequence↗

Regions of human chromosome 2 (2q32-q35) and mouse chromosome 1 show synteny with the pufferfish genome (Fugu rubripes).

We have isolated and sequenced a cosmid clone from the compact genome of the Japanese pufferfish (Fugu rubripes) containing portions of three genes that have the same order as in human. The gene order is microtubule-associated protein (MAP-2), myosin light chain (MYL-1), and carbamoyl phosphate synthetase (CPS III). The intron-exon organization of Fugu CPS III is identical with that of rat CPS I, although the equivalent genomic fragments of rat and Fugu CPS span 87.9 and 21 kb, respectively. This is the first report of a piscine CPS III genomic structure and predicts a close evolutionary link between CPS III and CPS I. The 8-kb intergenic region between MYL-1 and CPS gave no clear areas of transcription factor-binding sites by pairwise comparison with shark or rat CPS promoter regions. However, there was a match with the rat myosin light chain 2 (MLC-2) gene promoter and a MyoD transcription factor-binding site 874 bp upstream of the MYL-1 gene.

Amino Acid Sequence↗

Short-range linkage relationships, genomic organisation and sequence comparisons of a cluster of five HSP70 genes in Fugu rubripes.

Twelve cosmids containing sequences resembling genes encoding members of the 70-kDa heat-shock protein family, HSP70. have been isolated from Fugu rubripes. They can be broadly divided into three groups of overlapping cosmids. Restriction analysis and sequencing of one set of five cosmids have revealed five intronless Fugu HSP70 genes spanning 42 kb, arranged in a combined head-to-head, tail-to-tail and head-to-tail orientation. The levels of DNA and amino acid identity are very high with respect to one another, and are most similar to HSP70 sequences linked to the major histocompatibility complex (MHC) region in other species. Putative heat-shock consensus elements are identified. Non-HSP70 sequences with homology to known genes have been found physically linked to this Fugu HSP70 cluster: the Drosophila melanogaster SOL gene, the Drosophila melanogaster nemo gene, the Caenorhabditis elegans T17E9.1 gene and the sequence encoding the serine protease domain. The linkage relationships described here so far bear no resemblance to those of HSP70 in other organisms. Convergence of mammalian HSP70 and MHC class I and II loci probably occurred after fish had diverged.

Amino Acid Sequence↗

[Fugue and suicide].

The existence of dissociative fugue is doubted by many psychiatrists. We describe a 22-year-old patient who traveled about 600 km to Munich during a dissociative fugue and then exhibited an irreversible amnesia for a period of 24 h. There was a severe, clearly understandable conflict in the sense of a subjective stalemate situation which has been described as typical for dissociative fugue. The patient had a labile personality structure with insufficient coping strategies. It was possible to rule out other psychiatric or neurological disorders with sufficient certainty, and simulation was very unlikely. The conflict could not be satisfactorily solved, and the patient committed suicide 5 months later by jumping off a bridge.

Adult↗

Prediction of the prototype of the human Toll-like receptor gene family from the pufferfish, Fugu rubripes, genome.

The insect Toll family of proteins and their mammalian counterparts seemingly shared one common ancestor and evolved independently. Here we demonstrated that the prototype of the mammalian-type (M-type) Toll family is shared by the fish and humans. According to the draft of the pufferfish Fugu genome project, the signature Toll-IL-1 receptor homology domain (TIR domain) has been conserved during evolution. FuguTLR2, 3, 5, 7, 8 and 9 members correspond structurally to respective mammalian TLRs. One Fugu TLR showed equally high amino acid identity to human TLR1, 6 and 10, and we named it FuguTLR1. Fugu rubripes has genes for TLR21 and 22, which are unique to fish. One possible interpretation of these findings is that TLR1, 2, 3, 4, 5, 7, 8, 9, 21 and 22 existed in the ancestral genome common to fish and mammals, and that TLR4 was lost in the fish lineage, while TLR21 and 22 were lost in the mammalian lineage. Strikingly, a solitary ascidian, Halocynthia roretzi, has only a few Toll-like proteins, which, like Caenorhabditis elegans Toll, represent primitive ones before the expansion of the Toll family. Therefore, the expansion of TLR genes should have occurred earlier than fish, but not C. intestinalis, separated evolutionarily from mammals. These results infer that the appearance of the M-type innate system was completed before or concomitant with the appearance of acquired immunity. We interpret the present data to mean that the differences of TLRs identified in this study between fishes and humans may be rather peripheral, partially due to selection pressure exerted by pathogens in distinct environments.

Amino Acid Sequence↗

Characterization and expression analysis of CD3varepsilon and CD3gamma/delta in fugu, Takifugu rubripes.

CD3 is an essential component of the CD3-TCR complex. In this report, we describe the cloning, characterization, and expression analysis of the CD3varepsilon and CD3gamma/delta chain genes from fugu, Takifugu rubripes. Two distinct CD3varepsilon homologue cDNAs, designated as CD3varepsilon-1 and CD3varepsilon-2, and a CD3gamma/delta homologue cDNA were isolated from the fugu thymus. The deduced amino acid sequences of these cDNAs exhibit conserved essential CD3 chain motifs and overall structures. RT-PCR analysis demonstrated that the CD3varepsilon and CD3gamma/delta genes were expressed in lymphoid organs (e.g. thymus, head kidney, trunk kidney and spleen), mucosal tissues (gill, skin, and intestine), and peripheral blood leucocytes (PBL). The CD3 and TCRalpha genes were expressed only in the surface IgM- population, which were separated from PBL using an anti-fugu IgM monoclonal antibody. In addition, in situ hybridization confirmed that CD3-expressing cells were distributed randomly in the head kidney, trunk kidney, and spleen, but in the thymus were restricted to the lymphoid outer zone and epithelioid inner zone only. Collectively, these results suggest that CD3 molecules are useful markers for the identification of T cells in teleost fish. The present study thus provides a critical step in identifying T cells in this model organism.

Animals↗

AP1 genes in Fugu indicate a divergent transcriptional control to that of mammals.

The draft genomic sequence of the Japanese puffer fish, Fugu rubripes, has now been announced. This is the first complete sequence of a teleost fish and the second available vertebrate sequence, the first being that of human. For the first time, whole-genome comparisons between two vertebrates can be undertaken. Early analysis has suggested that there may be surprising differences in gene regulation between human and fish. In mammals, a gene commonly has several functions, and this may not always be the case in fish. Many gene families comprise more members in fish than they do in mammals, possibly because each fish gene has evolved an individual function. Complexities of gene regulation in mammals has hampered studies of all biological processes from cell proliferation to cell death. Determining the activities of the AP1 transcription factor proteins has been non-trivial. The AP1 complex typically comprises two proteins, a Jun (c-Jun, JunB, and JunD) and a Fos (c-Fos, FosB, Fra1, and Fra2). These proteins can form both homodimers and heterodimers among-themselves and can interact with additional proteins; thus, dissecting their individual roles has been difficult. We have determined that Fugu has more Jun and Fos genes than mammals, and if each proves to have a separate function, then addressing the roles of the individual AP1 proteins in Fugu may be simpler than in human.

Amino Acid Sequence↗

Cloning and expression of the reverse transcriptase component of pufferfish (Fugu rubripes) telomerase.

The enzyme telomerase is essential for maintaining the ends of linear chromosomes. It plays an important role in cell proliferation, differentiation, tumorigenesis and aging. Telomerase is composed of an RNA subunit (TR) and a reverse transcriptase catalytic subunit (TERT). We report here the cloning and characterization of the gene encoding the TERT subunit from a teleost fish, Fugu rubripes. This is the first fish TERT gene to be cloned. The fugu TERT (fTERT) gene comprises of 16 exons and 15 introns similar to the human TERT (hTERT), and encodes a 1074 amino acid protein. The fTERT protein showed 33% to 35% sequence identity to other vertebrate TERTs, and contained all the signature motifs of the TERT family. Analysis of the promoter region of fTERT showed the presence of several transcription factor binding sites (E2F-1, E-box, ER, Sp1 and USF sites) in common with the hTERT promoter, and whose binding factors are known to regulate hTERT. The fTERT gene is expressed in a variety of tissues, with high expression detected in the gill, testis, and ovary. fTERT expression was detected in an immortalized fugu eye-derived cell line. The level of expression was found to be higher in actively dividing cells and reduced at quiescence, suggesting cell cycle regulation of TERT and possibly telomerase activity, in this cell line.

Amino Acid Sequence↗

Prolactin gene expression and gill chloride cell activity in fugu Takifugu rubripes exposed to a hypoosmotic environment.

To evaluate a possible involvement of prolactin (PRL) in low-salinity tolerance of a marine pufferfish Takifugu rubripes, or fugu, gene-expression profiles of PRL in the pituitary and PRL receptor (PRLR) in the osmoregulatory organs were investigated in fish exposed to 25%-dilute seawater (SW). Following transfer from full-strength (100%) SW to 25% SW, plasma osmolality and Na(+) and Cl(-) levels were slightly decreased on day 1, which were restored on days 3 and 7. Expression levels of PRL mRNA in the pituitary was significantly increased in response to 25% SW transfer, which was in sharp contrast with a remarkable decrease in growth hormone (GH) mRNA levels. These profiles suggest that PRL and GH are involved in hyper- and hypoosmoregulation, respectively, as is the case with euryhaline teleosts. Expression levels of PRLR mRNA in the gill and intestine were not significantly different from the initial levels, whereas, PRLR mRNA expression in the kidney was significantly higher on day 7 than the initial levels. Although transfer to 25% SW did not affect the average size of Na(+)/K(+)-ATPase-immunoreactive chloride cells in the gills, both size and density of apical openings of chloride cells became significantly smaller after transfer to 25% SW. These findings suggest that the possible hypoosmotic action of PRL is mediated by PRLR expressed in the osmoregulatory organs, and that low-salinity tolerance of fugu may involve reduction of an ion-secreting function of gill chloride cells. To further evaluate long-term effects of the low-salinity environment on growth and osmoregulation, fugu were raised in 25% and 100% SW for a prolonged period of 8 weeks. They grew similarly in 25% and 100% SW, and there was no significant difference in body weight and standard length at any weekly sampling point. The plasma osmolality was maintained at about 345mOsm/kg.H(2)O in both media, whereas the gill Na(+)/K(+)-ATPase activity was significantly lower in 25% SW than 100% SW. Gene expression of PRL in the pituitary was higher in 25% SW than in 100% SW; conversely, expression levels of GH were lower in 25% SW than in 100% SW. These findings support a hyperosmotic action of PRL and a hypoosmotic, rather than growth-promoting, action of GH in this marine teleost.

Animals↗

Compact intergenic regions of the pufferfish genome facilitate isolation of gene promoters: characterization of Fugu 3'-phosphoadenosine 5'-phosphosulfate synthase 2 (fPapss2) gene promoter function in transgenic Xenopus.

The highly compact nature of the pufferfish (Fugu rubripes) genome renders it a useful tool not only for annotating coding regions within vertebrate genomes, but also for the identification of sequences important to gene regulation. Indeed, owing to this compaction it will be feasible in many instances to initiate analyses using entire intergenic regions when mapping gene promoters; a strategy that is very rarely feasible with the expanded genomes of other species. Stemming from our interest in studying promoters expressed in chondrocytes, we selected for study the intergenic region upstream of Fugu 3'-phosphoadenosine 5'-phosphosulfate synthase 2, fPapss2, a gene required for the normal development of cartilage extracellular matrix. Functional characterization of the entire fPapss2 5' intergenic region was carried out by monitoring expression of the enhanced green fluorescent protein (EGFP) gene reporter in the developing cartilage of transgenic Xenopus laevis. By evaluating a series of 5' intergenic region deletions we defined a minimal fPapss2 sequence of approximately 300 bp that was essential for EGFP expression in tadpole cartilage. This functional analysis of an entire Fugu intergenic region, combined with the efficiency of Xenopus transgenesis, serves as a model for the rapid characterization of evolutionarily-conserved regulatory regions of other pufferfish genes.

Animals↗

Molecular cloning of EDG-3 and N-Shc genes from the puffer fish, Fugu rubripes, and conservation of synteny with the human genome.

EDG-3 is a receptor for sphingosine-1-phosphate mapped on human chromosome 9q22.1-q22.2. We used the compact Fugu genome for its linkage analysis. The Fugu EDG-3 was composed of one intron and two exons, encoding a 384 amino acid protein that has 56.9% homology with the human EDG-3. Approximately 3 kb apart, a neuronal Shc (N-Shc) gene was identified. It spans 7 kb containing 12 coding exons, and has an overall 53.4% similarity with the human protein. We mapped the human N-Shc gene to chromosome 9q21.3-q22.2. This is the first report of the genomic structure and the linkage of these two genes conserved between Fugu and human.

Amino Acid Sequence↗

Characterisation of two genes for guanylate cyclase activator protein (GCAP1 and GCAP2) in the Japanese pufferfish, Fugu rubripes.

cDNA and genomic clones encoding guanylate cyclase activating proteins (GCAP1 and GCAP2) in the Japanese puffer fish (Fugu rubripes) were identified by probing, respectively, a retinal cDNA library and a whole genomic cosmid library with human GCAP1 and GCAP2 cDNA probes. Clones were identified as GCAP1 and GCAP2 on the basis of amino acid identity with the equivalent frog sequences and their placement into GCAP1 and GCAP2 clades within a GCAP phylogenetic tree. The Fugu genes have an identical four exon/three intron structure to GCAP1 and GCAP2 genes from other vertebrates but the introns are smaller, with the result that the four exons spread over approximately 1 kb of DNA in each case. The two genes are separated on to separate cosmids. However, the results of Southern analysis of the cosmids and of genomic DNA are consistent with a tail-to-tail gene arrangement, as in other species, but with a surprisingly large intergenic separation of around 18.7 kb. Recombinant Fugu GCAP1 failed to activate human retinal guanylate cyclase (retGC) in vitro although CD spectroscopy shows that the protein is folded with a similar secondary structure to that of human GCAP1. The failure to activate may be due therefore to a lack of molecular compatibility in this heterologous assay system.

Amino Acid Sequence↗

Identification of novel tropomyosin 1 genes of pufferfish (Fugu rubripes) on genomic sequences and tissue distribution of their transcripts.

Fugu genome database enabled us to identify two novel tropomyosin 1 (TPM1) genes through in silico data mining and isolation of their corresponding cDNAs in vivo. The duplicate TPM1 genes in Japanese pufferfish Fugu rubripes suggest that additional an ancient segmental duplication or whole genome duplication occurred in fish lineage, which, like many other reported Fugu genes, showed reduction in genomic size in comparison with their human homologue. Computer analysis predicted that the coiled-coil probabilities, that were thought to be the most major function of TPM, were the same between the two TPM1 isoforms. We confirmed that the tissue expression profiles of the two TPM1 genes differed from each other, which implied that changes in expression pattern could fix duplicated TPM1 genes although the two TPM1 isoforms appear to have similar function.

Animals↗

Organization of the Fugu rubripes Hox clusters: evidence for continuing evolution of vertebrate Hox complexes.

The clustered organization of Hox genes provides a powerful opportunity to examine gene gain and loss in evolution because physical linkage is a key diagnostic feature which allows homology to be established unambiguously. Furthermore, Hox genes play a key role in determination of axial and appendicular skeletal morphology and may be a key component of the evolution of diverse metazoan body forms. Despite suggestions that changes in Hox gene number played a role in evolution of metazoan body plans, there has been a general lack of evidence for such variation amongst gnathostomes (or indeed any vertebrate) and it has therefore been widely assumed that differential regulation may be the key element in all vertebrate Hox evolution. We have studied the Hox gene clusters of a teleost fish, Fugu rubripes, to test the possibility that Hox organization may have varied since the origin of jawed vertebrates. We have identified four Hox complexes in Fugu and found an unprecedented degree of variation when compared with tetrapod clusters. Our data show that: Fugu clusters are widely variant with respect to length; at least nine genes have been lost; there is a new group-2 paralogue; and pseudo-gene remnants of group-1 and group-3 paralogues were found in the Hoxc complex, when compared with the present mammalian clusters. We show that gene loss after duplication of the prototypical vertebrate Hox clusters is a key feature of both tetrapod and fish evolution.

Amino Acid Sequence↗

One INK4 gene and no ARF at the Fugu equivalent of the human INK4A/ARF/INK4B tumour suppressor locus.

The INK4A/ARF/INK4B locus, conserved in mammals, encodes three polypeptides that regulate cell proliferation via the pRb and p53 tumour suppressor pathways. The locus is mutated in many cancers. The related, tandemly-linked INK4A and INK4B genes encode the p16(INK4A) and p15(INK4B) members of the INK4 family of cyclin-dependent kinase inhibitors which block phosphorylation of pRb, whereas the third product, ARF, derived from an alternative reading frame of INK4A, regulates p53 activity. We assessed the status of this unusual locus in the puffer fish, Fugu rubripes, and identified two INK4 genes using degenerate PCR and hybridization analyses. Sequence conservation and conservation of synteny between human and Fugu predict one gene to be an INK4A or INK4B homologue and the other an INK4D homologue. Analysis of the Fugu INK4A/B gene and the surrounding 40-kb of genomic DNA did not reveal the presence of any ARF-encoding potential or another related INK4 gene. We conclude that the gene duplication event that generated adjacent INK4A and INK4B genes and the association of ARF with the ancestral INK4A gene occurred after the divergence of the lineage leading to mammals from fish. Thus, unlike mammals, the fish p53 and pRb tumour suppressor pathways are not regulated by a single locus.

Amino Acid Sequence↗

Putative pheromone receptors related to the Ca2+-sensing receptor in Fugu.

By a combination of PCR with degenerate primers and low stringency probing, we have isolated a large family of genes related to the Ca2+-sensing receptor from the genome of Fugu rubripes. One of the genes (type I) is the Fugu homologue of the Ca2+-sensing receptor. The remaining genes can be divided into five classes (type II-VI) on the bases of gene structure. In several types, the genes occur in clusters as tandem arrays. These genes appear to be the homologues of the vomeronasal pheromone receptors recently described in rodents. The Fugu genes are expressed in the tissues of the nose, suggesting that they may have a similar physiological role.

Animals↗

Lectins homologous to those of monocotyledonous plants in the skin mucus and intestine of pufferfish, Fugu rubripes.

We have characterized pufflectin, a novel mannose-specific lectin, from the skin mucus of the pufferfish, Fugu rubripes. Molecular mass estimations by gel filtration and matrix-assisted laser desorption ionization time-of-flight mass spectrometry and the SDS-PAGE pattern suggest that pufflectin is a homodimer composed of non-covalently associated subunits of 13 kDa. The full-length pufflectin cDNA consists of 527 bp, with 116 amino acid residues deduced from the open reading frame. The amino acid sequence of pufflectin shows no homology with any known animal lectin. Surprisingly, pufflectin shares sequence homology with mannose-binding lectins of monocotyledonous plants and has conserved two of three carbohydrate recognition domains of these plant lectins. The pufflectin gene is expressed in gills, oral cavity wall, esophagus, and skin. In addition, an isoform occurs exclusively in the intestine. Pufflectin differs from mannose-binding lectins purified from the blood plasma of Fugu. Whereas pufflectin did not agglutinate five bacterial species tested, it was demonstrated to bind to the parasitic trematode, Heterobothrium okamotoi. This finding suggests that pufflectin contributes to the parasite-defense system in Fugu.

Agglutination Tests↗