Loss of plakophilin 2 disrupts heart development in zebrafish

The desmosomal armadillo protein plakophilin 2 is the only plakophilin expressed in the heart, and mutations in the human plakophilin 2 gene result in arrhythmogenic right ventricular cardiomyopathy. To investigate loss of function, we knocked down plakophilin 2 by morpholino microinjection in zebrafish. This resulted in decreased heart rate, cardiac oedema, blood pooling, a failure of the heart to pattern correctly and a twisted tail. Co-injection of plakophilin 2 mRNA rescued the morphant phenotype, indicating the specificity of the knockdown. Desmosome numbers were decreased in morphant hearts and the plaque and midline structures of the desmosomes in the intercalated discs were disrupted when examined by electron microscopy. cmlc2 and vmhc expression at 48 hours post-fertilization (hpf) showed incomplete looping of the heart in morphant embryos by whole mount in situ hybridization, and bmp4 expression was expanded into the ventricle. The domain of expression of the heart marker nkx2.5 at 24 hpf was expanded. At the 18 somite stage, expression of the cardiogenic gene lefty2 was abolished in the left cardiac field, with concomitant increases in bmp4, spaw and lefty1 expression, likely resulting in the looping defects. These results indicate that plakophilin 2 has both structural and signalling roles in zebrafish heart development.

Effect of nanoparticle stabilization and physicochemical properties on exposure outcome: acute toxicity of silver nanoparticle preparations in zebrafish (Danio rerio)

Nanotechnology has vast potential for expanded development and novel application in numerous sectors of society. With growing use and applications, substantial production volumes and associated environmental release can be anticipated. Exposure effect of nanoparticles (NP) on biological systems may be intrinsic to their physicochemical properties introducing unknown associated risk. Herein, we expand the knowledge of health and environmental impact of silver nanoparticles (AgNPs), testing the acute toxicity of 14 AgNP preparations on developing zebrafish embryos (Danio rerio). Toxicological end points, including mortality, hatching rate, and heart rate were recorded. Concentration, stabilization agent and physicochemical properties were monitored as contributing outcome factors. Our findings indicate wide ranging LC50 24 h postfertilization values (0.487 ppm (0.315, 0.744 95% CI) to 47.89 ppm (18.45, 203.49 95% CI)), and indicate surface charge and ionic dissolution as key contributory factors in AgNP exposure outcome.

Insulin-like growth factor-2 regulates early neural and cardiovascular system development in zebrafish embryos

The insulin-like growth factor (IGF) family is essential for normal embryonic growth and development and it is highly conserved through vertebrate evolution. However, the roles that the individual members of the IGF family play in embryonic development have not been fully elucidated. This study focuses on the role of IGF-2 in zebrafish embryonic development. Two igf-2 genes, igf-2a and igf-2b, are present in the zebrafish genome. Antisense morpholinos were designed to knock down both igf-2 genes. The neural and cardiovascular defects in IGF-2 morphant embryos were then examined further using wholemount in situ hybridisation, TUNEL analysis and O-dianisidine staining. Knockdown of igf-2a or igf-2b resulted in ventralised embryos with reduced growth, reduced eyes, disrupted brain structures and a disrupted cardiovascular system, with igf-2b playing a more significant role in development. During gastrulation, igf-2a and igf-2b are required for development of anterior neural structures and for regulation of genes critical to dorsal-ventral patterning. As development proceeds, igf-2a and igf-2b play anti-apoptotic roles. Gene expression analysis demonstrates that igf-2a and igf-2b play overlapping roles in angiogenesis and cardiac outflow tract development. Igf-2b is specifically required for cardiac valve development and cardiac looping. Injection of a dominant negative IGF-1 receptor led to similar defects in angiogenesis and cardiac valve development, indicating IGF-2 signals through this receptor to regulate cardiovascular development. This is the first study describing two functional igf-2 genes in zebrafish. This work demonstrates that igf-2a and igf-2b are critical to neural and cardiovascular development in zebrafish embryos. The finding that igf-2a and igf-2b do not act exclusively in a redundant manner may explain why both genes have been stably maintained in the genome.

Mouse induced pluripotent stem cells

The recent discovery that it is possible to directly reprogramme somatic cells to an embryonic stem (ES) cell-like pluripotent state, by retroviral transduction of just four genes (Oct3/4, Sox2, c-Myc and Klf4), represents a major breakthrough in stem cell research. The reprogrammed cells, known as induced pluripotent stem (iPS) cells, possess many of the properties of ES cells, and represent one of the most promising sources of patient-specific cells for use in regenerative medicine. While the ultimate goal is the use of iPS cells in the treatment of human disease, much of the research to date has been carried out with murine cells, and improved mouse iPS cells have been shown to contribute to live chimeric mice that are germ-line competent. Very recently, it has been reported that iPS cells can be generated by three factors without c-Myc, and these cells give rise to chimeric mice with a reduced risk of tumour development.

Plakoglobin has both structural and signalling roles in zebrafish development

Plakoglobin, or gamma-catenin, is found in both desmosomes and adherens junctions and participates in Wnt signalling. Mutations in the human gene are implicated in the congenital heart disorder, arrhythmogenic right ventricular cardiomyopathy (ARVC), but the signalling effects of plakoglobin loss in ARVC have not been established. Here we report that knockdown of plakoglobin in zebrafish results in decreased heart size, reduced heartbeat, cardiac oedema, reflux of blood between heart chambers and a twisted tail. Wholemount in situ hybridisation shows reduced expression of the heart markers nkx2.5 at 24 hours post fertilisation (hpf), and cmlc2 and vmhc at 48 hpf, while there is lack of restriction of the valve markers notch1b and bmp4 at 48 hpf. Wnt target gene expression was examined by semi-quantitative RT-PCR and found to be increased in morphant embryos indicating that plakoglobin is antagonistic to Wnt signalling. Co-expression of the Wnt inhibitor, Dkk1, rescues the cardiac phenotype of the plakoglobin morphant. beta-catenin protein expression is increased in morphant embryos as is its colocalisation with E-cadherin in adherens junctions. Endothelial cells at the atrioventricular boundary of morphant hearts have an aberrant morphology, indicating problems with valvulogenesis. Morphants also have decreased numbers of desmosomes and adherens junctions in the intercalated discs. These results establish the zebrafish as a model for ARVC caused by loss of plakoglobin function and indicate that there are signalling as well as structural consequences of this loss.

Molecular cloning and expression analysis of two distinct β-glucosidase genes, bg1 and aven1, with very different biological roles from the thermophilic, saprophytic fungus Talaromyces emersonii

Recent sequencing of a number of fungal genomes has revealed the presence of multiple putative beta-glucosidases. Here, we report the cloning of two beta-glucosidase genes (bg1 and aven1), which have very different biological functions and represent two of a number of beta-glucosidases from Talaromyces emersonii. The bg1 gene, encoding a putative intracellular beta-glucosidase, shows significant similarity to other fungal glucosidases from glycosyl hydrolase family 1, known to be involved in cellulose degradation. Solka floc, methyl-xylose, gentiobiose, beech wood xylan, and lactose induced expression of bg1, whereas glucose repressed expression. A second beta-glucosidase gene isolated from T. emersonii, aven1, encodes a putative avenacinase, an enzyme that deglucosylates the anti-fungal saponin, avenacin, rendering it less toxic to the fungus. This gene displays high homology with other fungal saponin-hydrolysing enzymes and beta-glucosidases within GH3. A putative secretory signal peptide of 21 amino acids was identified at the N-terminus of the predicted aven1 protein sequence suggesting that this enzyme is extracellular. Furthermore, T. emersonii cultivated on oat plant biomass was shown to deglucosylate avenacin. The presence of the avenacinase transcript was confirmed by RT-PCR on RNA extracted from mycelia grown in the presence of avenacin. The expression pattern of aven1 on various carbon sources was distinctly different from that of bg1. Only methyl-xylose and gentiobiose induced transcription of aven1. Gentiobiose induces synthesis of a number of cellulase genes by T. emersonii and it may be a possible candidate for the natural cellulase inducer observed in Penicillium purpurogenum. This work represents the first report of an avenacinase gene from a thermophilic, saprophytic fungal source, and suggests that this gene is not exclusive to plant pathogens.

Identification of zygotic genes expressed at the midblastula transition in zebrafish

Early development of the embryo is directed by maternal gene products and characterised by limited zygotic gene activity, cell division synchrony and no cell motility in several vertebrates including fish and frogs. At the midblastula transition (MBT), zygotic transcription is grossly activated, cells become motile and cell divisions become asynchronous. The aim of this study was to identify genes whose expression is up-regulated at the MBT in zebrafish. Suppression subtractive hybridisation (SSH) was employed to isolate 48 unique cDNAs, 28 of which show significant similarity to known genes and 20 represent novel cDNAs. Twenty one of these genes, with potential roles in transcriptional regulation, cell cycle control, and embryonic patterning showed increased expression at the MBT. Our results demonstrate the value of SSH as a tool to clone novel, zygotic, developmentally regulated genes that may be important in the progression of the MBT and embryonic patterning.

Mannose 6-phosphate receptors in an ancient vertebrate, zebrafish

The endosome/lysosome system plays key roles in embryonic development, but difficulties posed by inaccessible mammalian embryos have hampered detailed studies. The accessible, transparent embryos of Danio rerio, together with the genetic and experimental approaches possible with this organism, provide many advantages over rodents. In mammals, mannose 6-phosphate receptors (MPRs) target acid hydrolases to endosomes and lysosomes, but nothing is known of acid hydrolase targeting in zebrafish. Here, we describe the sequence of the zebrafish cation-dependent MPR (CD-MPR) and cation-independent MPR (CI-MPR), and compare them with their mammalian orthologs. We show that all residues critical for mannose 6-phosphate (M6P) recognition are present in the extracellular domains of the zebrafish receptors, and that trafficking signals in the cytoplasmic tails are also conserved. This suggests that the teleost receptors possess M6P binding sites with properties similar to those of mammalian MPRs, and that targeting of lysosomal enzymes by MPRs represents an ancient pathway in vertebrate cell biology. We also determined the expression patterns of the CD-MPR and CI-MPR during embryonic development in zebrafish. Both genes are expressed from the one-cell stage through to the hatching period. In early embryos, expression is ubiquitous, but in later stages, expression of both receptors is restricted to the anterior region of the embryo, covering the forebrain, midbrain and hindbrain. The expression patterns suggest time- and tissue-specific functions for the receptors, with particular evidence for roles in neural development. Our study establishes zebrafish as a novel, genetically tractable model for in vivo studies of MPR function and lysosome biogenesis.

nanor, a novel zygotic gene, is expressed initially at the midblastula transition in zebrafish

A novel, developmentally regulated gene, nanor, was identified by suppression subtractive hybridization. It is first expressed following the midblastula transition (MBT), a critical developmental stage in the early vertebrate embryo when the zygotic genome is activated. The nanor cDNA (626bp) includes a complete open reading frame but neither the gene nor the deduced amino acid sequence shows significant similarity to any known gene or protein. Nanor encodes a 175 amino acid putative protein with a protein kinase C and three casein kinase II phosphorylation sites, an N-myristoylation site and an NFX-type zinc-finger domain, indicating a potential role in transcriptional regulation. Semi-quantitative RT-PCR, Northern blot, and in situ hybridization analysis revealed that nanor expression is developmentally regulated. It is initially expressed after the MBT at the sphere stage and during epiboly it is expressed in the forerunner cells. At 24 h post-fertilization, expression is solely anterior.

Insulin-like growth factor (IGF) signalling is required for early dorso-anterior development of the zebrafish embryo

The insulin-like growth factor (IGF) signalling pathway has been highly conserved in animal evolution and, in mammals and Xenopus, plays a key role in embryonic growth and development, with the IGF-1 receptor (IGF-1R) being a crucial regulator of the signalling cascade. Here we report the first functional role for the IGF pathway in zebrafish. Expression of mRNA coding for a dominant negative IGF-1R resulted in embryos that were small in size compared to controls and had disrupted head and CNS development. At its most extreme, this phenotype was characterized by a complete loss of head and eye structures, an absence of notochord and the presence of abnormal somites. In contrast, up-regulation of IGF signalling following injection of IGF-1 mRNA, resulted in a greatly expanded development of anterior structures at the expense of trunk and tail. IGF-1R knockdown caused a significant decrease in the expression of Otx2, Rx3, FGF8, Pax6.2 and Ntl, while excess IGF signalling expanded Otx2 expression in presumptive forebrain tissue and widened the Ntl expression domain in the developing notochord. The observation that IGF-1R knockdown reduced expression of two key organizer genes (chordin and goosecoid) suggests that IGF signalling plays a role in regulating zebrafish organizer activity. This is supported by the expression of IGF-1, IGF-2 and IGF-1R in shield-stage zebrafish embryos and the demonstration that IGF signalling influences expression of BMP2b, a gene that plays an important role in zebrafish pattern formation. Our data is consistent with a common pathway for integration of IGF, FGF8 and anti-BMPs in early vertebrate development.

Three-dimensional structure of a thermostable native cellobiohydrolase, CBH IB, and molecular characterization of the cel7 gene from the filamentous fungus, Talaromyces emersonii

The X-ray structure of native cellobiohydrolase IB (CBH IB) from the filamentous fungus Talaromyces emersonii, PDB 1Q9H, was solved to 2.4 A by molecular replacement. 1Q9H is a glycoprotein that consists of a large, single domain with dimensions of approximately 60 A x 40 A x 50 A and an overall beta-sandwich structure, the characteristic fold of Family 7 glycosyl hydrolases (GH7). It is the first structure of a native glycoprotein and cellulase from this thermophilic eukaryote. The long cellulose-binding tunnel seen in GH7 Cel7A from Trichoderma reesei is conserved in 1Q9H, as are the catalytic residues. As a result of deletions and other changes in loop regions, the binding and catalytic properties of T. emersonii 1Q9H are different. The gene (cel7) encoding CBH IB was isolated from T. emersonii and expressed heterologously with an N-terminal polyHis-tag, in Escherichia coli. The deduced amino acid sequence of cel7 is homologous to fungal cellobiohydrolases in GH7. The recombinant cellobiohydrolase was virtually inactive against methylumberiferyl-cellobioside and chloronitrophenyl-lactoside, but partial activity could be restored after refolding of the urea-denatured enzyme. Profiles of cel7 expression in T. emersonii, investigated by Northern blot analysis, revealed that expression is regulated at the transcriptional level. Putative regulatory element consensus sequences for cellulase transcription factors have been identified in the upstream region of the cel7 genomic sequence.

Cellular longevity: role of apoptosis and replicative senescence

Cellular longevity refers to the lifespan of an individual cell. Normal cells have a finite lifespan and typically die by undergoing apoptosis, or enter into a state of irreversible growth arrest, termed replicative senescence, at the end of that lifespan. The lifespan of a cell is a balance between pro-survival/anti-apoptotic and pro-apoptotic death-promoting factors. The role of heat shock proteins, Bcl-2 family members, antioxidant molecules, and telomere length and telomerase activity in the regulation of apoptosis and replicative senescence, will be discussed.

Zebrafish insulin-like growth factor-I receptor: molecular cloning and developmental expression

The biological actions of the insulin-like growth factors (IGFs) are mediated primarily by the IGF-I receptor (IGF-IR), and the IGF family has been highly conserved throughout vertebrate evolution. In this study we report the isolation of a 3 kb cDNA clone for the zebrafish IGF-IR that includes the complete 3' untranslated region and polyA tail and mapping of the receptor gene to zebrafish linkage group 7. The open reading frame deduced from the cDNA sequence encompasses the juxtamembrane and protein tyrosine kinase portions of the receptor, and is 70 and 67% identical to the corresponding regions of the IGF-IRs of the turbot and Xenopus, respectively. By RT-PCR, zebrafish IGF-IR expression was detected from early blastula to early larval stages of development. Using whole mount in situ hybridization, IGF-IR expression was detected after gastrulation. Expression was evident in most tissues but was particularly evident in the tail, in eye and ear primordia and in the brain.

Cyclin-dependent kinase 8 is expressed both maternally and zygotically during zebrafish embryo development

Cyclin-dependent kinase 8 (cdk8) regulates transcription by phosphorylating RNA polymerase II and TFIIH. The mechanism of zygotic transcription activation during vertebrate embryonic development is poorly understood. Here we describe the cloning and developmental expression pattern of zebrafish cdk8 mRNA. It is highly conserved, sharing 79% DNA and 95% amino acid sequence identity with human cdk8, thereby indicating an important role for the protein. Northern blotting and whole mount in situ hybridisation revealed expression of zebrafish cdk8 maternally, following the onset of zygotic transcription at the mid-blastula transition (MBT) and throughout embryonic development.

Atlantic salmon HNF-3/forkhead: cDNA sequence, evolution, expression, and functional analysis

We report the isolation and characterization of a cDNA encoding an HNF-3 family member (as HNF-3) from Atlantic salmon (Salmo salar L). The important functional domains of HNF-3 proteins that have been characterized previously are revealed by segments of high identity along the alignment of the asHNF-3 with winged helix/forkhead amino acid sequences isolated from other species. A comparison of asHNF-3 cDNA and genomic DNA indicated that there were no introns present in the asHNF-3 gene. Expression of asHNF-3 protein in adult salmon tissues was not exclusive to liver but was also present in the pancreas and intestine. An RT-PCR analysis performed on salmon development showed that asHNF3 expression is detectable before gastrulation at the mid blastula transition stage. Functional analysis of the asHNF-3 protein using a characterized HNF-3 consensus binding site demonstrated that the protein can recognize and bind to specific HNF-3 consensus sequences. We also report the identification of a novel HNF3 binding site in the promoter of the Atlantic salmon transferrin gene.

Transcriptional regulation of expression of the rainbow trout albumin gene by estrogen

Estrogens modulate the expression of many liver-specific genes in oviparous species. For instance, expression of the estrogen receptor and vitellogenin genes is strongly up-regulated by estradiol in rainbow trout liver. Using hepatocyte primary cultures, we demonstrate that trout albumin (Alb) gene is also regulated by this hormone. Indeed, treatment of hepatocytes with 1 microM estradiol led, after 24 h, to a dramatic decrease in Alb mRNA level. To investigate the mechanism of this down-regulation, run-off experiments were performed and mRNA half-lives were determined in the presence and absence of estradiol. The results show that the down-regulation of Alb mRNA expression by estrogens occurs only at the transcriptional level.

Salmon HNF1: cDNA sequence, evolution, tissue specificity and binding to the salmon serum albumin promoter

cDNA clones coding for the transcription factor HNF1 have been isolated from Atlantic salmon (Salmo salar L.). The 559 amino acid residue long encoded protein shows high conservation, with respect to other species, of the domains necessary for DNA-binding: the HNF1 atypical homeodomain, the POU related sequence and the dimerisation domain. Alignment with rat HNF1 protein reveals that the transcription activation domains ADI and ADIII are relatively conserved in the fish sequence whereas ADII is not. Phylogenetic analysis indicates that higher vertebrate HNF1s and the related variant HNF1s (vHNF1s) are more closely related to each other than any of them is to Salmon HNF1, suggesting that the duplication event from which HNF1 and vHNF1 genes arose occurred after the divergence of the tetrapod and teleost ancestors. Northern blot analysis show a single transcript, of about 2.6 kb, which is not exclusive to liver but is also present in intestine, kidney and spleen. Using polymerase chain reaction (PCR) we have isolated the salmon albumin gene promoter which contains, upstream of the TATA box, a potential binding site for HNF1. The salmon HNF1 protein synthesized by in vitro transcription-translation of the full-length cDNA is able to bind specifically with equivalent affinities to either the rat or salmon albumin promoter.

Cloning and sequencing of the Atlantic salmon (Salmo salar) cytochrome c oxidase subunit III gene (coxIII) and analysis of coxIII expression during parr-smolt transformation

Smoltification is the process whereby salmon alter their metabolism in preparation for movement from freshwater to seawater. Differential screening of a cDNA library prepared from post-smolt salmon liver mRNA led to the selection of a smoltification-induced sequence. Analysis of this cDNA revealed that it partially encoded subunit III of the enzyme cytochrome c oxidase. The complete coxIII sequence was amplified from salmon genomic DNA using consensus oligonucleotides based on ATPase 6 and tRNA(GLY) sequences from Pacific salmonid species. Cytochrome c oxidase subunit III liver mRNA levels were found to be significantly increased in salmon smolts. Northern blot analysis revealed a coxIII transcript of approximately 750 bp in all salmon tissues tested except blood. The DNA sequence of coxIII employs the mammalian mitochondrial genetic code and is strongly conserved when compared with that of other species.

Sequence analysis of a second cDNA encoding Atlantic salmon (Salmo salar) serum albumin

Two similar, but distinct, cDNAs for Atlantic salmon serum albumin have been isolated from the same salmon liver. Comparison between the asSA-1 and asSA-2 sequences reveals 1% overall sequence difference.

The salmon gene encoding apolipoprotein A-I: cDNA sequence, tissue expression and evolution

A cDNA encoding an apolipoprotein (Apo) has been isolated from the Atlantic salmon (Salmo salar) and sequenced. It encodes a peptide of 258 amino acids (aa), including a signal peptide of 18 aa, with 5'- and 3'-untranslated regions of the mRNA of 12 and 329 nucleotides, respectively. The protein has structural features in common with other Apo's of human and avian origin, including conserved sequences in the signal peptide and a series of internal repeats of 22 aa. The sequence has been identified as salmon Apo A-I (sApoA-I), and has 23% aa identity with human ApoA-I. Northern-blot analysis using the sApoA-I cDNA probe against total RNA prepared from several salmon tissues detects the expression of this gene in liver, intestine and muscle. A phylogenetic analysis reveals that the mammalian ApoA-I, ApoA-IV and Apo-E aa sequences are more closely related to each other than any of them are to sApoA-I. This suggests that the duplication events, from which A-I, A-IV and E arose, occurred after the divergence of the tetrapod and teleost ancestors.

Sequence of a cDNA clone encoding an Atlantic salmon ribosomal protein

We report here the nucleotide sequence of a cDNA clone encoding a salmon (Salmo salar) ribosomal (r) protein. The encoded protein shows 62.3% and 62% similarity with the L14 and L18 r-proteins in Xenopus laevis and rat, respectively.

Atlantic salmon (Salmo salar) serum albumin: cDNA sequence, evolution, and tissue expression

Atlantic salmon serum albumin is one of the most abundant proteins in salmon liver, representing 1.6% of all clones in a cDNA library made from salmon liver RNA. The DNA from a number of clones was sequenced to reveal an open reading frame of 1,827 bases encoding a 608-amino-acid protein. The sequenced 5' untranslated region is 69 bases long and the 3' untranslated region contains two putative polyadenylation signals and poly(A) tail. Sequence analysis of different clones indicates the presence of a second cDNA for salmon serum albumin. Multiple alignments of salmon serum albumin deduced amino acid sequence with Xenopus laevis, rat, bovine, and human serum albumins shows significant conservation of cysteine residues. The triple domain structure of serum albumin proteins is maintained. Unlike mammalian systems where serum albumin expression appears to be specific to liver only, salmon serum albumin is expressed in muscle also.

Chicken apolipoprotein A-I: cDNA sequence, tissue expression and evolution

Using an antibody against chicken apolipoprotein (apo) A-I, we identified multiple cDNA clones for the protein in two intestinal cDNA libraries in lambda gt11. The complete nucleotide sequence of chicken apoA-I cDNA was determined. The sequence predicts a mature protein of 240 amino acids, a 6-amino acid propeptide and an 18-amino acid signal peptide. Using a 32P-cDNA probe, we detected the presence of apoA-I mRNA in 21 day old chicken intestine, liver, kidney, spleen, breast muscle and brain. The primary sequence of apoA-I contains numerous tandem repeats of 11 and 22 residues in a manner similar to the mammalian proteins. Our analysis of apoA-I sequences from human, rabbit, dog, rat, and chicken indicates that the rate of amino acid substitution is considerably faster in the rat lineage than in other mammalian lineages.