Comparison of the activity of carp and rat beta-actin gene regulatory sequences in tilapia and rainbow trout embryos

Cloning, characterization, and transcriptional activity of β-actin promoter of African catfish (Clarias gariepinus)

Selection of suitable promoters is crucial for the efficient expression of exogenous genes in transgenic animals. Although one of the most effective promoters, the β-actin promoter, has been widely studied in fish species, it still remains unknown in the economical important African catfish (Clarias gariepinus). In this study, the β-actin promoter of African catfish (cgβ-actinP) was cloned and characterized. In addition, recombinant plasmid pcgβ-actinP-EGFP with enhanced green fluorescent protein (GFP) gene as the reporter gene was constructed to verify the transcriptional activity. We obtained a cgβ-actinP fragment length of 1405 bp, consisting 104 bp of the 5' proximal promoter, 96 bp of the first exon, and 1205 bp of the first intron. Similar to those of other fish species, cgβ-actinP contains three key transcription regulatory elements (CAAT box, CArG motif, and TATA box). GFP-specific fluorescent signals were detected in chicken embryonic fibroblasts cells (DF-1 cells) transfected with pcgβ-actinP-EGFP, which was approximately 1.11 times of the positive control. In addition, GFP was effectively expressed in zebrafish larvae microinjected with linearized cgβ-actinP-EGFP, with expression rate reaching approximately 49.84%. Our data indicate that cgβ-actinP could be a potential candidate promoter in the practice of constructing "all fish" transgenic fish.

Molecular characterization of the giant freshwater prawn (Macrobrachium rosenbergii) beta-actin gene promoter

Constitutive promoters are important tools for gene function studies and transgenesis. The Beta-actin (actb1) gene promoter has been isolated from many species but remains to be cloned from the giant freshwater prawn (Macrobrachium rosenbergii). In this study, we cloned and characterized the Mractb1 gene promoter. Two alternative promoters were identified for the Mractb1 gene, which direct the generation of two transcripts with different 5′ untranslated regions. Three CpG islands were predicted in the upstream sequence, which are intimately related to transcription initiation and promoter activity. In addition to the CCAAT-box and the CArG-box, molecular dissection of the flanking sequence revealed the existence of one negative and two positive elements in the upstream region and the first intron. Finally, the Mractb1 promoter demonstrated comparative activity to the carp (Cyprinus carpio) actb1 promoter. Our investigations provide a valuable genetic tool for gene function studies and shed light on the regulation of the Mractb1 gene.

Functional Analysis of the Promoter Region of Japanese Flounder (Paralichthys olivaceus) β-actin Gene: A Useful Tool for Gene Research in Marine Fish

A newly isolated Japanese flounder (Paralichthys olivaceus) β-actin promoter and its derivative compact construct Poβ-actinΔ−1080/−801Δ−500/−201 have recently been demonstrated to promote ectopic gene expression in cell lines. Different Poβ-actin promoter deletion mutants were constructed and functionally characterized. Mutational analyses by dual-luciferase detected that three regulatory elements, including one enhancer (−1399/−1081) and two silencers (−1080/−801, −500/−201) in the first intron. The sequence located at −1399/−1081 was determined to significantly affect promoter activity. Additionally, the first exon (−1489/−1400) could also remarkably promote the β-actin promoter activity. In the following transduction application, we removed the two silencers and generated a compact reconstruct promoter/enhancer (Poβ-actinΔ−1080/−801Δ−500/−201), which exhibited relatively stronger promoter activity compared with Poβ-actin. Furthermore, the green fluorescent protein (GFP) transgenic stable flounder cell line was obtained by the reconstructed Poβ-actinΔ−1080/−801Δ−500/−201 promoter. Our study provided the potential application of Japanese flounder β-actin, particularly Poβ-actinΔ−1080/−801Δ−500/−201, in ectopic gene expression in the future.

Function and regulation domains of a newly isolated putative β-actin promoter from pacific white shrimp

Current development of transgenic shrimp research has been hampered due to the lack of the suitable promoters and efficient transfection methods for crustaceans. A 1642 bp sequence, containing 5'-upstream sequence, exon 1, intron 1 and partial exon 2, which is responsible for transcriptional initiation of the newly reported shrimp β-actin (actinT1), has been isolated from the Pacific white shrimp (Litopenaeus vannamei) and named as SbaP. To determine its function and potential application in marine biotechnology, the sequence and functional domains were examined by constitutive expression of the luciferase reporter gene. We have identified 5' regions that play a central role in the expression of the β-actin gene. The proximal promoter (-1642/-1325) contains two highly conserved transcriptional sites, CCAAT box and CArG motif. Two negative (-1140/-924, -222/-21) and one positive (-810/-425) regulatory elements have been identified in intron1. Transient transfection assay with a construct containing proximal promoter and enhancer (SbaPΔ-222/+1Δ-1325/-924) regions of the shrimp β-actin coupled with luciferase and EGFP (enhanced green fluorescent protein) showed that the promoter was not only functional in sf21 cells, but promoter activity was more than 8-fold higher than a viral-origin promoter (ie1, white spot syndrome virus immediate early gene promoter). Furthermore, SbaPΔ-222/+1Δ-1325/-924 drove a successful expression of luciferase injection assay in vivo injection and also showed higher promoter activity than the ie1 promoter, suggesting that the expression vectors constructed with SbaPΔ-222/+1Δ-1325/-924 have important potential in gene transfer studies for shrimp and other crustacean species.

Isolation of yellow catfish β-actin promoter and generation of transgenic yellow catfish expressing enhanced yellow fluorescent protein

Yellow catfish (Pelteobagrus fulvidraco Richardson) is one of the most important freshwater farmed species in China. However, its small size and slow growth rate limit its commercial value. Because genetic engineering has been a powerful tool to develop and improve fish traits for aquaculture, we performed transgenic research on yellow catfish in order to increase its size and growth rate. Performing PCR with degenerate primers, we cloned a genomic fragment comprising 5'-flanking sequence upstream of the initiation codon of β-actin gene in yellow catfish. The sequence is 1,017 bp long, containing the core sequence of proximal promoter including CAAT box, CArG motif and TATA box. Microinjecting the transgene construct Tg(beta-actin:eYFP) of the proximal promoter fused to enhanced yellow fluorescent protein (eYFP) reporter gene into zebrafish and yellow catfish embryos, we found the promoter could drive the reporter to express transiently in both embryos at early development. Screening the offspring of five transgenic zebrafish founders developed from the embryos microinjected with Tg(ycbeta-actin:mCherry) or 19 yellow catfish founders developed from the embryos microinjected with Tg(beta-actin:eYFP), we obtained three lines of transgenic zebrafish and one transgenic yellow catfish, respectively. Analyzing the expression patterns of the reporter genes in transgenic zebrafish (Tg(ycbeta-actin:mCherry)nju8/+) and transgenic yellow catfish (Tg(beta-actin:eYFP)nju11/+), we found the reporters were broadly expressed in both animals. In summary, we have established a platform to make transgenic yellow catfish using the proximal promoter of its own β-actin gene. The results will help us to create transgenic yellow catfish using "all yellow catfish" transgene constructs.

The short-lived fish Nothobranchius furzeri as a new model system for aging studies

Genetic and pharmacological research on aging is hampered by the lifespan of available vertebrate models. We recently initiated studies on Nothobranchius furzeri, a species with a maximum life expectancy in captivity of just three months which represents the shortest documented captive lifespan for a vertebrate. Further research on N. furzeri has demonstrated that 1. Short lifespan is tied with explosive growth and accelerated sexual maturation. 2. Short lifespan is correlated with expression of age-related behavioral and histological changes. 3. Lifespan and expression of age-related markers can be modulated by water temperature. 4. Resveratrol, a drug characterized for its life-extending action in Caenorhabditis elegans and Drosophila, increases lifespan and retards expression of age-related markers. 5. Aging-related genes can be easily isolated by homology cloning. Finally, different populations or species of Nothobranchius show large-scale differences in captive lifespan. In the last three years, N. furzeri has moved from biological curiosity to a promising model system for drug validation. Furthermore, this species occupies a favorable position in the Teleost's "tree of life". It is very close to the Japanese Medaka, and close to the pufferfishes and stickleback and might represent a very useful model for comparative genomics of aging.

Fish as bioreactors: transgene expression of human coagulation factor VII in fish embryos

A plasmid containing human coagulation factor VII (hFVII) complementary DNA regulated by a cytomegalovirus promoter was microinjected into fertilized eggs of zebrafish, African catfish, and tilapia. The active form of hFVll was detected in the fish embryos by various assays. This positive expression of human therapeutic protein in fish embryos demonstrates the possibility of exploitation of transgenic fish as bioreactors.

Transposition and targeting of the prokaryotic mobile element IS30 in zebrafish

We provide evidence that a prokaryotic insertion sequence (IS) element is active in a vertebrate system. The transposase of Escherichia coli element IS30 catalyzes both excision and integration in extrachromosomal DNA in zebrafish embryos. The transposase has a pronounced target preference, which is shown to be modified by fusing the enzyme to unrelated DNA binding proteins. Joining the transposase to the cI repressor of phage lambda causes transposition primarily into the vicinity of the lambda operator in E. coli, and linking to the DNA binding domain of Gli1 also directs the recombination activity of transposase near to the Gli1 binding site in zebrafish. Our results demonstrate the possibility of fusion transposases to acquire novel target specificity in both prokaryotes and eukaryotes.

Fish can be first--advances in fish transgenesis for commercial applications

Over the past 15 years researchers have generated stable lines of several species of transgenic fish important for aquaculture. 'All-fish' growth hormone (GH) gene constructs and antifreeze protein (AFP) genes have been successfully introduced into the fish genome resulting in a significant acceleration of growth rate and an increase in cold and freeze tolerance. However, neither gene modification is completely understood; there are still questions to be resolved. Expression rates are still low, producing variable growth enhancement rates and less than desired levels of freeze resistance. Transgene strategies are also being developed to provide improved pathogen resistance and modified metabolism for better utilization of the diet. Additional challenges are to tailor the genetically modified fish strains to prevent release of the modified genes into the environment.

Isolation and characterisation of tilapia beta-actin promoter and comparison of its activity with carp beta-actin promoter

The regulatory sequence including proximal promoter, untranslated exon 1 and intron 1 of the beta-actin gene from tilapia (Oreochromis niloticus) has been isolated and spliced to a beta-galactosidase reporter gene to test its activity. Comparisons of promoter activity have been carried out with three different constructs: (1) 1.6 kb tilapia beta-actin regulatory sequence, (2) 1.5 kb carp beta-actin regulatory sequence, and (3) 4.7 kb carp beta-actin regulatory sequence. Although the 1.6 kb tilapia beta-actin regulatory sequence gave slightly different expression patterns in tilapia embryos assayed by in situ X-gal staining, no difference was observed in expression level when the tilapia sequence was compared with the 4.7 kb carp beta-actin regulatory sequence by quantitative assay. In comparison with the 1.5 kb carp beta-actin regulatory sequence, the 1.6 kb tilapia beta-actin regulatory sequence gave higher expression levels in tilapia embryos, while a reverse result was observed in zebrafish embryos. In cell transfection experiments, the 1.6 kb tilapia beta-actin regulatory sequence showed three to four times better activity in blue gill cells than either the 4.7 kb carp beta-actin or the 1.5 kb carp beta-actin regulatory sequences. The 1.6 kb tilapia beta-actin regulatory sequence also drove higher reporter gene activity in somatic cells of tilapia than did the 4.7 kb carp beta-actin regulatory sequence following direct injection of constructs into muscle. Therefore, taken together, the data demonstrate that the tilapia beta-actin promoter can be used as an efficient regulatory sequence to produce autotransgenic tilapia.

Glowing zebrafish: integration, transmission, and expression of a single luciferase transgene promoted by noncovalent DNA-nuclear transport peptide complexes

The development of vehicles driving foreign DNA into the cell nucleus is essential for effective cellular gene transfer applications. We report that noncovalent binding of nuclear localization signal (NLS) peptides to plasmid DNA enhances nuclear uptake of the DNA and promotes germline integration, inheritance, and expression of a single copy of a luciferase reporter gene in zebrafish. As few as 10 DNA-NLS complexes (0.06 fg plasmid DNA) cytoplasmically injected are sufficient to produce germline-transgenic zebrafish bearing a single copy of the transgene. This corresponds to a 10(5)-fold reduction in DNA concentration compared to commonly used procedures. Use of 10(3) or 10(4) DNA-NLS complexes augments the number of transgene integrations, which occur mostly within 1-4 distinct insertion sites in the genome. In situ hybridization analyses and transmission studies show that transgene integration into the germline and somatic tissues is mosaic, and that the extent of mosaicism is negatively correlated with the amount of DNA-NLS injected. In addition, a larger proportion of zebrafish harboring a single copy of the transgene expresses luciferase, albeit at a 10-fold lower level than those containing numerous transgene insertions. The data demonstrate the potential use of nuclear targeting peptides noncovalently bound to vector DNA to enhance the efficiency of biotechnological nonviral gene transfer applications.

Active transgenes in zebrafish are enriched in acetylated histone H4 and dynamically associate with RNA Pol II and splicing complexes

We have investigated the functional organization of active and silent integrated luciferase transgenes in zebrafish, with the aim of accounting for the variegation of transgene expression in this species. We demonstrate the enrichment of transcriptionally active transgenes in acetylated histone H4 and the dynamic association of the transgenes with splicing factor SC35 and RNA Pol II. Analysis of interphase nuclei and extended chromatin fibers by immunofluorescence and in situ hybridization reveals a co-localization of transgenes with acetylated H4 in luciferase-expressing animals only. Enrichment of expressed transgenes in acetylated H4 is further demonstrated by their co-precipitation from chromatin using anti-acetylated H4 antibodies. Little correlation exists, however, between the level of histone acetylation and the degree of transgene expression. In transgene-expressing zebrafish, most transgenes co-localize with Pol II and SC35, whereas no such association occurs in non-expressing individuals. Inhibition of Pol II abolishes transgene expression and disrupts association of transgenes with SC35, although inactivated transgenes remains enriched in acetylated histones. Exposure of embryos to the histone deacetylation inhibitor TSA induces expression of most silent transgenes. Chromatin containing activated transgenes becomes enriched in acetylated histones and the transgenes recruit SC35 and Pol II. The results demonstrate a correlation between H4 acetylation and transgene activity, and argue that active transgenes dynamically recruit splicing factors and Pol II. The data also suggest that dissociation of splicing factors from transgenes upon Pol II inhibition is not a consequence of changes in H4 acetylation.

Expression of a novel piscine growth hormone gene results in growth enhancement in transgenic tilapia (Oreochromis niloticus)

Several lines of transgenic G1 and G2 tilapia fish (Oreochromis niloticus) have been produced following egg injection with gene constructs carrying growth hormone coding sequences of fish origin. Using a construct in which an ocean pout antifreeze promoter drives a chinook salmon growth hormone gene, dramatic growth enhancement has been demonstrated, in which the mean weight of the 7 month old G2 transgenic fish is more than three fold that of their non transgenic siblings. Somewhat surprisingly G1 fish transgenic for a construct consisting of a sockeye salmon metallothionein promoter spliced to a sockeye salmon growth hormone gene exhibited no growth enhancement, although salmon transgenic for this construct do show greatly enhanced growth. The growth enhanced transgenic lines were also strongly positive in a radio-immuno assay for the specific hormone in their serum, whereas the non growth enhanced lines were negative. Attempts to induce expression from the metallothionein promoter by exposing fish to increased levels of zinc were also unsuccessful. Homozygous transgenic fish have been produced from the ocean pout antifreeze/chinook salmon GH construct and preliminary trials suggest that their growth performance is similar to that of the hemizygous transgenics. No abnormalities were apparent in the growth enhanced fish, although minor changes to skull shape and reduced fertility were noted in some fish. There is also preliminary evidence for improved food conversion ratios when growth enhanced transgenic tilapia are compared to their non-transgenic siblings. The long term objective of this study is to produce lines of tilapia which are both growth enhanced and sterile, so offering improved strains of this important food fish for aquaculture.

Activator effect of coinjected enhancers on the muscle-specific expression of promoters in zebrafish embryos

The transient expression of reporter gene constructs in embryos provides a powerful tool to characterise cis-acting transcriptional elements of the genes involved in development. In the present study, we have analysed the expression pattern of several muscle-specific and ubiquitous regulatory sequences in microinjected zebrafish embryos. By using a fast and reproducible coinjection strategy, the mosaic expression of lacZ reporter gene was monitored in wholemount embryos injected with sequences containing putative enhancer elements and a carp myosin heavy chain promoter/lacZ reporter construct. We have found that a 0.9-kb myosin heavy chain (MyHC) proximal promoter containing several putative myogenic regulatory factors (MRF) binding sites is sufficient to restrict lacZ expression to the skeletal muscle fibres of prim-6 stage zebrafish embryos. Expression of a rat-derived foetal myosin light chain enhancer (MyLC) and different fragments of a carp beta-actin regulatory region together with the MyHC promoter were compared by accumulating the type, number and spatial distribution of beta-galactosidase-expressing cells on an expression map. beta-galactosidase activity increased similarly whether the MyLC enhancer was ligated to the promoter/ reporter construct directly or when coinjected as a separate fragment whilst skeletal muscle specificity was retained. The coinjection of two different forms of the beta-actin regulatory elements also showed a marked effect on the MyHC promoter activity. The coinjection of putative enhancers with minimal promoter constructs and subsequent analysis of the transient expression pattern in the developing embryos provides a rapid and simple technique to identify cis acting activator elements of genes expressed in the vertebrate embryo.