Liver-specific and seasonal expression of transgenic Atlantic salmon harboring the winter flounder antifreeze protein gene

The role of antifreeze genes in the tolerance of cold stress in the Nile tilapia (Oreochromis niloticus)

BACKGROUND

Tilapia is one of the most essential farmed fishes in the world. It is a tropical and subtropical freshwater fish well adapted to warm water but sensitive to cold weather. Extreme cold weather could cause severe stress and mass mortalities in tilapia. The present study was carried out to investigate the effects of cold stress on the up-regulation of antifreeze protein (AFP) genes in Nile tilapia (Oreochromis niloticus). Two treatment groups of fish were investigated (5 replicates of 15 fish for each group in fibreglass tanks/70 L each): 1) a control group; the fish were acclimated to lab conditions for two weeks and the water temperature was maintained at 25 °C during the whole experimental period with feeding on a commercial diet (30% crude protein). 2) Cold stress group; the same conditions as the control group except for the temperature. Initially, the temperature was decreased by one degree every 12 h. The fish started showing death symptoms when the water temperature reached 6-8 °C. In this stage the tissue (muscle) samples were taken from both groups. The immune response of fish exposed to cold stress was detected and characterized using Differential Display-PCR (DD-PCR).

RESULTS

The results indicated that nine different up-regulation genes were detected in the cold-stressed fish compared to the control group. These genes are Integrin-alpha-2 (ITGA-2), Gap junction gamma-1 protein-like (GJC1), WD repeat-containing protein 59 isoform X2 (WDRP59), NUAK family SNF1-like kinase, G-protein coupled receptor-176 (GPR-176), Actin cytoskeleton-regulatory complex protein pan1-like (PAN-1), Whirlin protein (WHRN), Suppressor of tumorigenicity 7 protein isoform X2 (ST7P) and ATP-binding cassette sub-family A member 1-like isoform X2 (ABCA1). The antifreeze gene type-II amplification using a specific PCR product of 600 bp, followed by cloning and sequencing analysis revealed that the identified gene is antifreeze type-II, with similarity ranging from 70 to 95%. The in-vitro transcribed gene induced an antifreeze protein with a molecular size of 22 kDa. The antifreeze gene, ITGA-2 and the WD repeat protein belong to the lectin family (sugar-protein).

CONCLUSIONS

In conclusion, under cold stress, Nile tilapia express many defence genes, an antifreeze gene consisting of one open reading frame of approximately 0.6 kbp.

Interpretation of the Genotype by Tissue Interactions of Four Genes (AFP1, CIRP, YB-1, and HMGB1) in Takifugu rubripes Under Different Low-Temperature Conditions

Background: The differential expression of the same gene in different tissues could be due to the genotype effect, tissue effect, and/or genotype × tissue interactions. However, the genetic mechanisms responsible for this differential expression have not been reported to date.

Methods: Four resistance genes to low temperature, the genes for antifreeze protein (AFP), cold induced RNA binding protein (CIRP), high mobility group protein box-1 (HMGB1), and Y-box binding protein (YB-1), were measured by PCR in the liver, spleen, kidney, brain, heart, intestine, muscle, gonad, and skin of Takifugu rubripes cultured under different temperature conditions (18, 13, 8, and 5°C). Split-split-plot analysis of variance, additive main effects and multiplicative interaction (AMMI) and genotype main effects and genotype × environment interaction (GGE) biplot analysis were used to evaluate the effects of genotype × tissue interactions on gene expression.

Results: The results of split-split-plot analysis of variance showed that water temperature has a significant effect on the expression of T. rubripes cold resistant genes, while tissue × gene interaction has a highly significant effect on it. AMMI analysis showed that the contributions of genotype, tissue, and genotype × tissue interactions to the total variation in gene expression followed two trends: 1) as temperature decreased, the gene effect increased gradually and the genotype × tissue interaction decreased gradually; 2) the gene effect at 18 and 13°C was significantly lower than that at 8 and 5°C, while the interaction at 18 and 13°C was significantly higher than that at 8 and 5°C. GGE analysis showed that: at all temperatures except 8°C, the expression rankings of all four genes were highly positively correlated in all tissues except muscle; the expression stability of the genes was the same at 18°C/13°C and at 8°C/5°C; and AFP1 showed the best expression and stability among the four genes.

Conclusion: 8°C/5°C as the suitable temperature for such experiments for T. rubripes. Among the four antifreeze genes evaluated in this study, AFP1 had the best expression and stability.

Identification and Functional Characterization of Antifreeze Protein and Its Mutants in Dendroctonus armandi (Coleoptera: Curculionidae: Scolytinae) Larvae Under Cold Stress

Dendroctonus armandi (Tsai and Li) (Coleoptera: Curculionidae: Scolytinae) is considered to be the most destructive forest pest in the Qinling and Bashan Mountains of China. Low winter temperatures limit insect's populations, distribution, activity, and development. Insects have developed different strategies such as freeze-tolerance and freeze-avoidance to survive in low temperature conditions. In the present study, we used gene cloning, real-time polymerase chain reaction (PCR), RNA interference (RNAi), and heterologous expression to study the function of the D. armandi antifreeze protein gene (DaAFP). We cloned the 800 bp full-length cDNA encoding 228 amino acids of DaAFP and analyzed its structure using bioinformatics analysis. The DaAFP amino acid sequence exhibited 24-86% similarity with other insect species. The expression of DaAFP was high in January and in the larvae, head, and midgut of D. armandi. In addition, the expression of DaAFP increased with decreasing temperature and increasing exposure time. RNAi analysis also demonstrated that AFP plays an important role in the cold tolerance of overwintering larvae. The thermal hysteresis and antifreeze activity assay of DaAFP and its mutants indicated that the more regular the DaAFP threonine-cystine-threonine (TXT) motif, the stronger the antifreeze activity. These results suggest that DaAFP plays an essential role as a biological cryoprotectant in overwintering D. armandi larvae and provides a theoretical basis for new pest control methods.

Genetic Engineering of Livestock: The Opportunity Cost of Regulatory Delay

Genetically engineered (GE) livestock were first reported in 1985, and yet only a single GE food animal, the fast-growing AquAdvantage salmon, has been commercialized. There are myriad interconnected reasons for the slow progress in this once-promising field, including technical issues, the structure of livestock industries, lack of public research funding and investment, regulatory obstacles, and concern about public opinion. This review focuses on GE livestock that have been produced and documents the difficulties that researchers and developers have encountered en route. Additionally, the costs associated with delayed commercialization of GE livestock were modeled using three case studies: GE mastitis-resistant dairy cattle, genome-edited porcine reproductive and respiratory syndrome virus-resistant pigs, and the AquAdvantage salmon. Delays of 5 or 10 years in the commercialization of GE livestock beyond the normative 10-year GE product evaluation period were associated with billions of dollars in opportunity costs and reduced global food security.

The properties, biotechnologies, and applications of antifreeze proteins

By natural selection, organisms evolve different solutions to cope with extremely cold weather. The emergence of an antifreeze protein gene is one of the most momentous solutions. Antifreeze proteins possess an importantly functional ability for organisms to survive in cold environments and are widely found in various cold-tolerant species. In this review, we summarize the origin of antifreeze proteins, describe the diversity of their species-specific properties and functions, and highlight the related biotechnology on the basis of both laboratory tests and bioinformatics analysis. The most recent advances in the applications of antifreeze proteins are also discussed. We expect that this systematic review will contribute to the comprehensive knowledge of antifreeze proteins to readers.

A brief review of applications of antifreeze proteins in cryopreservation and metabolic genetic engineering

Antifreeze proteins (AFPs) confer the ability to survive at subzero temperatures and are found in many different organisms, including fish, plants, and insects. They prevent the formation of ice crystals by non-colligative adsorption to the ice surface and are essential for the survival of organisms in cold environments. These proteins are also widely used for cryopreservation, food technology, and metabolic genetic engineering over a range of sources and recipient cell types. This review summarizes successful applications of AFPs in the cryopreservation of animals, insects, and plants, and discusses challenges encountered in cryopreservation. Applications in metabolic genetic engineering are also described, specifically with the overexpression of AFP genes derived from different organisms to provide freeze protection to sensitive crops seasonally exposed to subzero temperatures. This review will provide information about potential applications of AFPs in the cryopreservation of animals and plants as well as in plant metabolic genetic engineering in hopes of furthering the development of cold-tolerant organisms.

Laboratory-Scale Isolation of Insect Antifreeze Protein for Cryobiology

Micromolar concentrations of hyperactive antifreeze proteins (AFPs) from insects can prevent aqueous solutions from freezing down to at least −6 °C. To explore cryopreservation of cells, tissues and organs at these temperatures without ice formation, we have developed a protocol to reliably produce ultrapure Tenebrio molitor AFP from cold-acclimated beetle larvae reared in the laboratory. The AFP was prepared from crude larval homogenates through five cycles of rotary ice-affinity purification, which can be completed in one day. Recovery of the AFP at each step was >90% and no impurities were detected in the final product. The AFP is a mixture of isoforms that are more active in combination than any one single component. Toxicity testing of the purified AFP in cell culture showed no inhibition of cell growth. The production process can easily be scaled up to industrial levels, and the AFP used in cryobiology applications was recovered for reuse in good yield and with full activity.

The Glaciozyma antarctica genome reveals an array of systems that provide sustained responses towards temperature variations in a persistently cold habitat

Extremely low temperatures present various challenges to life that include ice formation and effects on metabolic capacity. Psyhcrophilic microorganisms typically have an array of mechanisms to enable survival in cold temperatures. In this study, we sequenced and analysed the genome of a psychrophilic yeast isolated in the Antarctic region, Glaciozyma antarctica. The genome annotation identified 7857 protein coding sequences. From the genome sequence analysis we were able to identify genes that encoded for proteins known to be associated with cold survival, in addition to annotating genes that are unique to G. antarctica. For genes that are known to be involved in cold adaptation such as anti-freeze proteins (AFPs), our gene expression analysis revealed that they were differentially transcribed over time and in response to different temperatures. This indicated the presence of an array of adaptation systems that can respond to a changing but persistent cold environment. We were also able to validate the activity of all the AFPs annotated where the recombinant AFPs demonstrated anti-freeze capacity. This work is an important foundation for further collective exploration into psychrophilic microbiology where among other potential, the genes unique to this species may represent a pool of novel mechanisms for cold survival.

Modification of Animal Products for Fat and Other Characteristics

This chapter includes information about modification of animal products using biotechnology and the importance of different modifications on the natural composition. The species considered for modified products include beef and dairy cattle, sheep, goats, poultry, and a wide variety of fishes. Moreover, the discussion includes the importance of animal food, nongenetically engineered animal modified food products, genetically engineered animal modified food items primarily for meat, milk, or egg and genetically engineered animal food along the transgenic approach for animal welfare. Modern biotechnology can improve productivity, consistency, and quality of alter animal food, fiber, and medical products. The transgenic technology is potentially valuable to alter characters of economic importance in a rapid and precise way. The food safety issue related to genetic engineering is also included in this chapter. The harm of such modified food and transgenic strategy should also be understood by the reader along with its advantages. In this context, transgenic approaches in animal biotechnology are under discussion that ranges from animal food production to their adverse effects.

Antifreeze peptides and glycopeptides, and their derivatives: potential uses in biotechnology

Antifreeze proteins (AFPs) and glycoproteins (AFGPs), collectively called AF(G)Ps, constitute a diverse class of proteins found in various Arctic and Antarctic fish, as well as in amphibians, plants, and insects. These compounds possess the ability to inhibit the formation of ice and are therefore essential to the survival of many marine teleost fishes that routinely encounter sub-zero temperatures. Owing to this property, AF(G)Ps have potential applications in many areas such as storage of cells or tissues at low temperature, ice slurries for refrigeration systems, and food storage. In contrast to AFGPs, which are composed of repeated tripeptide units (Ala-Ala-Thr)_n with minor sequence variations, AFPs possess very different primary, secondary, and tertiary structures. The isolation and purification of AFGPs is laborious, costly, and often results in mixtures, making characterization difficult. Recent structural investigations into the mechanism by which linear and cyclic AFGPs inhibit ice crystallization have led to significant progress toward the synthesis and assessment of several synthetic mimics of AFGPs. This review article will summarize synthetic AFGP mimics as well as current challenges in designing compounds capable of mimicking AFGPs. It will also cover our recent efforts in exploring whether peptoid mimics can serve as structural and functional mimics of native AFGPs.

Direct visualization of spruce budworm antifreeze protein interacting with ice crystals: basal plane affinity confers hyperactivity

Antifreeze proteins (AFPs) protect certain organisms from freezing by adhering to ice crystals, thereby preventing their growth. All AFPs depress the nonequilibrium freezing temperature below the melting point; however AFPs from overwintering insects, such as the spruce budworm (sbw) are 10-100 times more effective than most fish AFPs. It has been proposed that the exceptional activity of these AFPs depends on their ability to prevent ice growth at the basal plane. To test the hypothesis that the hyperactivity of sbwAFP results from direct affinity to the basal plane, we fluorescently tagged sbwAFP and visualized it on the surface of ice crystals using fluorescence microscopy. SbwAFP accumulated at the six prism plane corners and the two basal planes of hexagonal ice crystals. In contrast, fluorescently tagged fish type III AFP did not adhere to the basal planes of a single-crystal ice hemisphere. When ice crystals were grown in the presence of a mixture of type III AFP and sbwAFP, a hybrid crystal shape was produced with sbwAFP bound to the basal planes of truncated bipyramidal crystals. These observations are consistent with the blockage of c-axial growth of ice as a result of direct interaction of sbwAFP with the basal planes.

Tissue specific expression of antifreeze protein and growth hormone transgenes driven by the ocean pout (Macrozoarces americanus) antifreeze protein OP5a gene promoter in Atlantic salmon (Salmo salar)

Previous research aimed at producing genetically improved salmon broodstock for aquaculture led to the creation of two lines of transgenic Atlantic salmon using gene constructs that were derived in part from the ocean pout OP5a antifreeze protein (AFP) gene. One of the lines was produced using an OP5a AFP gene in which the 5' region of the promoter was removed (termed t-OP5a-AFP), and the other line contains a growth hormone (GH) transgene (EO-1alpha) that consists of a chinook salmon GH cDNA driven by a truncated OP5a AFP promoter that is almost identical to that of the t-OP5a-AFP construct. The similarity of the promoter regions of these transgenes provided an opportunity to evaluate their tissue specific expression patterns. Expression of mRNA was evaluated using Northern blot and RT-PCR techniques. The results demonstrate that the AFP and GH trangenes were expressed in almost all body tissues, suggesting that the promoter region of the OP5a AFP gene lacks tissue specific elements. Northern analysis revealed that expression of the t-OP5a-AFP gene was considerably greater than that of the EO-1alpha GH transgene. Only the spleen tissue of the GH transgenics showed a visible band of hybridization. In contrast clear bands of hybridization were evident in all tissues, except for blood cells, of the AFP transgenics with heart, liver and brain tissue showing the highest levels of mRNA expression. This higher level of expression could be attributable to the presence of introns in the t-OP5a-AFP transgene. Since the GH transgenic salmon grow considerably faster than non-transgenics the low levels of GH transgene expression in this line were clearly sufficient to produce the desired rapid growth phenotype. In contrast the levels of AFP expression were inadequate to impart any improvement in the freeze resistance of the AFP transgenic salmon.

Fluorescence microscopy evidence for quasi-permanent attachment of antifreeze proteins to ice surfaces

Many organisms are protected from freezing by the presence of extracellular antifreeze proteins (AFPs), which bind to ice, modify its morphology, and prevent its further growth. These proteins have a wide range of applications including cryopreservation, frost protection, and as models in biomineralization research. However, understanding their mechanism of action remains an outstanding challenge. While the prevailing adsorption-inhibition hypothesis argues that AFPs must bind irreversibly to ice to arrest its growth, other theories suggest that there is exchange between the bound surface proteins and the free proteins in solution. By conjugating green fluorescence protein (GFP) to a fish AFP (Type III), we observed the binding of the AFP to ice. This was accomplished by monitoring the presence of GFP-AFP on the surface of ice crystals several microns in diameter using fluorescence microscopy. The lack of recovery of fluorescence after photobleaching of the GFP component of the surface-bound GFP-AFP shows that there is no equilibrium surface-solution exchange of GFP-AFP and thus supports the adsorption-inhibition mechanism for this type of AFP. Moreover, our study establishes the utility of fluorescently labeled AFPs as a research tool for investigating the mechanisms underlying the activity of this diverse group of proteins.

Cold-loving microbes, plants, and animals--fundamental and applied aspects

Microorganisms, plants, and animals have successfully colonized cold environments, which represent the majority of the biosphere on Earth. They have evolved special mechanisms to overcome the life-endangering influence of low temperature and to survive freezing. Cold adaptation includes a complex range of structural and functional adaptations at the level of all cellular constituents, such as membranes, proteins, metabolic activity, and mechanisms to avoid the destructive effect of intracellular ice formation. These strategies offer multiple biotechnological applications of cold-adapted organisms and/or their products in various fields. In this review, we describe the mechanisms of microorganisms, plants, and animals to cope with the cold and the resulting biotechnological perspectives.

Expression of endogenous and exogenous growth hormone (GH) messenger (m) RNA in a GH-transgenic tilapia (Oreochromis niloticus)

We have previously produced transgenic fish from crosses between a wild-type female tilapia (Oreochromis niloticus) and a G transgenic male. This line of growth-enhanced tilapia carries a single copy of a chinook salmon (s) growth hormone (GH) gene spliced to an ocean pout antifreeze promoter (OPA-FPcsGH) co-ligated to a carp beta-actin/lacZ reporter gene construct, integrated into the tilapia genome. Because little is known about the expression sites of transgenes, we have characterised the gene expression patterns of sGH and tilapia (t)GH in transgenic tilapia using a newly established real-time PCR to measure the absolute mRNA amounts of both hormones. The sGH gene, which was expected to be expressed mainly in liver, was also found to be expressed in other organs, such as gills, heart, brain, skeletal muscle, kidney, spleen, intestine and testes. However, in pituitary no sGH mRNA but only tGH mRNA was found. Tilapia GH mRNA in wild-type pituitary amounted to 226 +/- 30 pg/microg total RNA but in transgenics only to 187 +/- 43 pg/microg total RNA. Liver exhibited the highest level of sGH mRNA (8.3 +/- 2.5 pg/microg total RNA) but the extrahepatic sites expressed considerable amounts of sGH mRNA ranging from 4.1 +/- 2.0 pg/microg total RNA in gills to 0.2 +/- 0.08 pg/microg total RNA in kidney. The widespread expression of the sGH gene is assumed to be due to the tissue specificity of the type III AFP gene promoter. It is assumed that our transgenic experiments, which in contrast to some other approaches caused no obvious organ abnormalities, mimick the GH expression during ontogeny. Because sGH mRNA is expressed both in liver and in extrahepatic sites it may not only promote secretion and release of liver-derived (endocrine) IGF-I leading to an overall growth enhancement but also stimulate IGF-I expression within the different organs in a paracrine/autocrine manner and, thus, further promote organ growth.

Enhancing the activity of a beta-helical antifreeze protein by the engineered addition of coils

The effectiveness of natural antifreeze proteins in inhibiting the growth of a seed ice crystal seems to vary with protein size. Here we have made use of the extreme regularity of the beta-helical antifreeze protein from the beetle Tenebrio molitor to explore systematically the relationship between antifreeze activity and the area of the ice-binding site. Each of the 12-amino acid, disulfide-bonded central coils of the beta-helix contains a Thr-Xaa-Thr ice-binding motif. By adding coils to, and deleting coils from, the seven-coil parent antifreeze protein, we have made a series of constructs with 6-11 coils. Misfolded forms of these antifreezes were removed by ice affinity purification to accurately compare the specific activity of each construct. There was a 10-100-fold gain in activity upon going from six to nine coils, depending on the concentration that was compared. Activity was maximal for the nine-coil construct, which gave a freezing point depression of 6.5 C degrees at 0.7 mg/mL, but actually decreased for the 10- and 11-coil constructs. This small loss in activity might result from the accumulation of a slight mismatch between the spacing of the ice-binding threonine residues and the O atoms of the ice lattice.

Suppression subtractive hybridization cDNA libraries to identify differentially expressed genes from contrasting fish habitats

Suppression subtractive hybridization complementary DNA libraries identified differentially expressed genes in liver tissue of winter flounder collected from the highly impacted Raritan-Hudson estuary versus those from less industrialized estuaries farther south in New Jersey. Distinct transcript profiles emerged in the fish from these different habitats. A total of 251 clones from the forward (upregulated with anthropogenic impact) and reverse (downregulated with anthropogenic impact) subtracted libraries were sequenced. In the upregulated library immune response transcripts, including complement C-3, C-7, factor H, factor Bf/C2, differentially regulated trout protein 1, and the antimicrobial hepcidin, indicated the pollution-impacted fish were under a high viral or bacterial load. Transcripts for cytochrome P450 1A, P450 3A, and glutathione S-transferase, important components of phase I and II metabolism of xenobiotics, were found in the upregulated-with-pollution library. Vitellogenins I and II and egg envelope protein (zp) appeared to be downregulated. A homologue of the tumor suppressor p33(ING1) (down) and hepatocyte growth factor-like protein (up) may indicate liver damage or hepatocellular carcinoma or hepatoma. These expression patterns, confirmed by quantitative polymerase chain reaction, indicate that transcript analysis is a useful method for assessing the health of local habitats and the organisms therein.

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.

Antifreeze proteins of teleost fishes

Marine teleosts at high latitudes can encounter ice-laden seawater that is approximately 1 degrees C colder than the colligative freezing point of their body fluids. They avoid freezing by producing small antifreeze proteins (AFPs) that adsorb to ice and halt its growth, thereby producing an additional non-colligative lowering of the freezing point. AFPs are typically secreted by the liver into the blood. Recently, however, it has become clear that AFP isoforms are produced in the epidermis (skin, scales, fin, and gills) and may serve as a first line of defense against ice propagation into the fish. The basis for the adsorption of AFPs to ice is something of a mystery and is complicated by the extreme structural diversity of the five antifreeze types. Despite the recent acquisition of several AFP three-dimensional structures and the definition of their ice-binding sites by mutagenesis, no common ice-binding motif or even theme is apparent except that surface-surface complementarity is important for binding. The remarkable diversity of antifreeze types and their seemingly haphazard phylogenetic distribution suggest that these proteins might have evolved recently in response to sea level glaciation occurring just 1-2 million years ago in the northern hemisphere and 10-30 million years ago around Antarctica. Not surprisingly, the expression of AFP genes from different origins can also be quite dissimilar. The most intensively studied system is that of the winter flounder, which has a built-in annual cycle of antifreeze expression controlled by growth hormone (GH) release from the pituitary in tune with seasonal cues. The signal transduction pathway, transcription factors, and promoter elements involved in this process are just beginning to be characterized.

Low-temperature increases the yield of biologically active herring antifreeze protein in Pichia pastoris

Antifreeze proteins and antifreeze glycoproteins are structurally diverse molecules that share a common property in binding to ice crystals and inhibiting ice crystal growth. Type II fish antifreeze protein of Atlantic herring (Clupea harengus harengus) is unique in its requirement of Ca(2+) for antifreeze activity. In this study, we utilized the secretion vector pGAPZalpha A to express recombinant herring antifreeze protein (WT) and a fusion protein with a C-terminal six-histidine tag (WT-6H) in yeast Pichia pastoris wild-type strain X-33 or protease-deficient strain SMD1168H. Both recombinant proteins were secreted into the culture medium and properly folded and functioned as the native herring antifreeze protein. Furthermore, our studies demonstrated that expression at a lower temperature increased the yield of the recombinant protein dramatically, which might be due to the enhanced protein folding pathway, as well as increased cell viability at lower temperature. These data suggested that P. pastoris is a useful system for the production of soluble and biologically active herring antifreeze protein required for structural and functional studies.