Production of transgenic tilapia with Brockmann bodies secreting [desThrB30] human insulin

Identification of Fish Species and Targeted Genetic Modifications Based on DNA Analysis: State of the Art

Food adulteration is one of the most serious problems regarding food safety and quality worldwide. Besides misleading consumers, it poses a considerable health risk associated with the potential non-labeled allergen content. Fish and fish products are one of the most expensive and widely traded commodities, which predisposes them to being adulterated. Among all fraud types, replacing high-quality or rare fish with a less valuable species predominates. Because fish differ in their allergen content, specifically the main one, parvalbumin, their replacement can endanger consumers. This underlines the need for reliable, robust control systems for fish species identification. Various methods may be used for the aforementioned purpose. DNA-based methods are favored due to the characteristics of the target molecule, DNA, which is heat resistant, and the fact that through its sequencing, several other traits, including the recognition of genetic modifications, can be determined. Thus, they are considered to be powerful tools for identifying cases of food fraud. In this review, the major DNA-based methods applicable for fish meat and product authentication and their commercial applications are discussed, the possibilities of detecting genetic modifications in fish are evaluated, and future trends are highlighted, emphasizing the need for comprehensive and regularly updated online database resources.

Dual-agonist incretin peptides from fish with potential for obesity-related Type 2 diabetes therapy - A review

The long-acting glucagon-like peptide-1 receptor (GLP1R) agonist, semaglutide and the unimolecular glucose-dependent insulinotropic polypeptide receptor (GIPR)/GLP1R dual-agonist, tirzepatide have been successfully introduced as therapeutic options for patients with Type-2 diabetes (T2DM) and obesity. Proglucagon-derived peptides from phylogenetically ancient fish act as naturally occurring dual agonists at the GLP1R and the glucagon receptor (GCGR) with lamprey GLP-1 and paddlefish glucagon being the most potent and effective in stimulating insulin release from BRIN-BD11 clonal β-cells. These peptides were also the most effective in lowering blood glucose and elevating plasma insulin concentrations when administered intraperitoneally to overnight-fasted mice together with a glucose load. Zebrafish GIP acts as a dual agonist at the GIPR and GLP1R receptors. Studies with the high fat-fed mouse, an animal model with obesity, impaired glucose-tolerance and insulin-resistance, have shown that twice-daily administration of the long-acting analogs [D-Ala²]palmitoyl-lamprey GLP-1 and [D-Ser²]palmitoyl-paddlefish glucagon over 21 days improves glucose tolerance and insulin sensitivity. This was associated with β-cell proliferation, protection of β-cells against apoptosis, decreased pancreatic glucagon content, improved lipid profile, reduced food intake and selective alteration in the expression of genes involved in β-cell stimulus-secretion coupling. In insulin-deficient Glu^CreERT2;ROSA26-eYFP transgenic mice, the peptides promoted an increase in β-cell mass with positive effects on transdifferentiation of glucagon-producing to insulin-producing cells. Naturally occurring fish dual agonist peptides, particularly lamprey GLP-1 and paddlefish glucagon, provide templates for development into therapeutic agents for obesity-related T2DM.

Sweet fish: Fish models for the study of hyperglycemia and diabetes

Fish are good for your health in more ways than you may expect. For one, eating fish is a common dietary recommendation for a healthy diet. However, fish have much more to provide than omega-3 fatty acids to your circulatory system. Some fish species now serve as important and innovative model systems for diabetes research, providing novel and unique advantages compared with classical research models. Not surprisingly, the largest share of diabetes research in fish occurs in the laboratory workhorse among fish, the zebrafish (Danio rerio). Established as a genetic model system to study development, these small cyprinid fish have eventually conquered almost every scientific discipline and, over the past decade, have emerged as an important model system for metabolic diseases, including diabetes mellitus. In this review we highlight the practicability of using zebrafish to study diabetes and hyperglycemia, and summarize some of the recent research and breakthroughs made using this model. Equally exciting is the appearance of another emerging discipline, one that is taking advantage of evolution by studying cases of naturally occurring insulin resistance in fish species. We briefly discuss two such models in this review, namely the rainbow trout (Oncorhynchus mykiss) and the cavefish (Astyanax mexicanus).

Progress and biotechnological prospects in fish transgenesis

The history of transgenesis is marked by milestones such as the development of cellular transdifferentiation, recombinant DNA, genetic modification of target cells, and finally, the generation of simpler genetically modified organisms (e.g. bacteria and mice). The first transgenic fish was developed in 1984, and since then, continuing technological advancements to improve gene transfer have led to more rapid, accurate, and efficient generation of transgenic animals. Among the established methods are microinjection, electroporation, lipofection, viral vectors, and gene targeting. Here, we review the history of animal transgenesis, with an emphasis on fish, in conjunction with major developments in genetic engineering over the past few decades. Importantly, spermatogonial stem cell modification and transplantation are two common techniques capable of revolutionizing the generation of transgenic fish. Furthermore, we discuss recent progress and future biotechnological prospects of fish transgenesis, which has strong applications for the aquaculture industry. Indeed, some transgenic fish are already available in the current market, validating continued efforts to improve economically important species with biotechnological advancements.

Ancestral genomic duplication of the insulin gene in tilapia: An analysis of possible implications for clinical islet xenotransplantation using donor islets from transgenic tilapia expressing a humanized insulin gene

Tilapia, a teleost fish, have multiple large anatomically discrete islets which are easy to harvest, and when transplanted into diabetic murine recipients, provide normoglycemia and mammalian-like glucose tolerance profiles. Tilapia insulin differs structurally from human insulin which could preclude their use as islet donors for xenotransplantation. Therefore, we produced transgenic tilapia with islets expressing a humanized insulin gene. It is now known that fish genomes may possess an ancestral duplication and so tilapia may have a second insulin gene. Therefore, we cloned, sequenced, and characterized the tilapia insulin 2 transcript and found that its expression is negligible in islets, is not islet-specific, and would not likely need to be silenced in our transgenic fish.

A review of piscine islet xenotransplantation using wild-type tilapia donors and the production of transgenic tilapia expressing a "humanized" tilapia insulin

Most islet xenotransplantation laboratories have focused on porcine islets, which are both costly and difficult to isolate. Teleost (bony) fish, such as tilapia, possess macroscopically visible distinct islet organs called Brockmann bodies which can be inexpensively harvested. When transplanted into diabetic nude mice, tilapia islets maintain long-term normoglycemia and provide human-like glucose tolerance profiles. Like porcine islets, when transplanted into euthymic mice, they are rejected in a CD4 T-cell-dependent manner. However, unlike pigs, tilapia are so phylogenetically primitive that their cells do not express α(1,3)Gal and, because tilapia are highly evolved to live in warm stagnant waters nearly devoid of dissolved oxygen, their islet cells are exceedingly resistant to hypoxia, making them ideal for transplantation within encapsulation devices. Encapsulation, especially when combined with co-stimulatory blockade, markedly prolongs tilapia islet xenograft survival in small animal recipients, and a collaborator has shown function in diabetic cynomolgus monkeys. In anticipation of preclinical xenotransplantation studies, we have extensively characterized tilapia islets (morphology, embryologic development, cell biology, peptides, etc.) and their regulation of glucose homeostasis. Because tilapia insulin differs structurally from human insulin by 17 amino acids, we have produced transgenic tilapia whose islets stably express physiological levels of humanized insulin and have now bred these to homozygosity. These transgenic fish can serve as a platform for further development into a cell therapy product for diabetes.

Encapsulated piscine (tilapia) islets for diabetes therapy: studies in diabetic NOD and NOD-SCID mice

BACKGROUND

Our goal was to improve islet transplantation as a therapy for patients with type I diabetes mellitus. Because human donor islets are scarce, we are studying islet xenografts in the diabetic NOD mouse model. We hypothesize that optimal xenoislet survival will be achieved by the combination of donor islet immunoisolation with recipient immunosuppression. We and others have studied adult and neonatal porcine islets as sources of tissue for microencapsulated islet xenografts, but we believe it is also advantageous to consider using islets from fish, which can be raised in large numbers relatively quickly and economically. Therefore, in this study, we have evaluated the function of microencapsulated xenogeneic piscine (tilapia) islets transplanted intraperitoneally (IP) in NOD mice in the presence of CD4(+) T-cell depletion and/or costimulatory blockade.

METHODS

Spontaneously diabetic NOD mice or streptozotocin (STZ)-diabetic NOD-SCID mice were transplanted IP with microencapsulated tilapia islets. Recipient immunosuppression included anti-CD4 mAb, CTLA4-Ig, anti-CD80 mAb, anti-CD86 mAb, or anti-CD154 mAb, alone or in combination. Graft function was evaluated by blood glucose (BG) levels, intravenous (IV) and oral glucose tolerance tests (GTTs), histologic and immunohistochemical analyses of grafts, and flow cytometric analysis of peritoneal cells.

RESULTS

Encapsulated tilapia islets normalized random BG levels for up to 210 days in NOD-SCID mice. In diabetic NOD mice, encapsulated tilapia islets were rejected on day 11 ± 4 with a peritoneal infiltrate of macrophages, eosinophils, B cells, occasional neutrophils, but few T cells. Immunohistochemical staining demonstrated the presence of murine IgG on tilapia islets within capsules of rejecting, non-immunosuppressed mice, as well as murine IgG-positive lymphocytes in the layer of host cells surrounding those capsules. These findings suggested that our barium (Ba)-gelled alginate capsules are permeable to IgG and that anti-piscine antibodies may be involved in the rejection of encapsulated tilapia islets in untreated mice. No single immunosuppressive agent prolonged encapsulated tilapia islet survival in NOD mice, but the combination of CTLA4-Ig plus anti-CD154 mAb extended tilapia islet graft survival until rejection at 119 ± 20 days and inhibited host cell recruitment to the peritoneal cavity. Triple treatment with CTLA4-Ig, anti-CD154 mAb, and anti-CD4 mAb allowed graft survival for 157 ± 35 days with little evidence of a host cellular reaction. IV and oral glucose tolerance tests (GTTs) of recipients with functioning xenografts demonstrated remarkably normal metabolic function.

CONCLUSIONS

We conclude that microencapsulated tilapia islets can survive long term with excellent metabolic control in diabetic mice given targeted immunosuppression, suggesting that cross-species physiological incompatibility may not compromise the applicability of this novel approach for future clinical applications. We predict that an improved microcapsule that prevents the entrance of IgG will enhance tilapia islet survival in this model, possibly allowing the application of this technique with limited or no immunosuppression.

Gene transfer and mutagenesis mediated by Sleeping Beauty transposon in Nile tilapia (Oreochromis niloticus)

The success of gene transfer has been demonstrated in many of vertebrate species, whereas the efficiency of producing transgenic animals remains pretty low due to the random integration of foreign genes into a recipient genome. The Sleeping Beauty (SB) transposon is able to improve the efficiency of gene transfer in zebrafish and mouse, but its activity in tilapia (Oreochromis niloticus) has yet to be characterized. Herein, we demonstrate the potential of using the SB transposon system as an effective tool for gene transfer and insertional mutagenesis in tilapia. A transgenic construct pT2/tiHsp70-SB11 was generated by subcloning the promoter of tilapia heat shock protein 70 (tiHsp70) gene, the SB11 transposase gene and the carp β-actin gene polyadenylation signal into the second generation of SB transposon. Transgenic tilapia was produced by microinjection of this construct with in vitro synthesized capped SB11 mRNA. SB11 transposon was detected in 28.89 % of founders, 12.9 % of F1 and 43.75 % of F2. Analysis of genomic sequences flanking integrated transposons indicates that this transgenic tilapia line carries two copies of SB transposon, which landed into two different endogenous genes. Induced expression of SB11 gene after heat shock was detected using reverse transcription PCR in F2 transgenic individuals. In addition, the Cre/loxP system was introduced to delete the SB11 cassette for stabilization of gene interruption and bio-safety. These findings suggest that the SB transposon system is active and can be used for efficient gene transfer and insertional mutagenesis in tilapia.

New insights into the signaling system and function of insulin in fish

Fish have provided essential information about the structure, biosynthesis, evolution, and function of insulin (INS) as well as about the structure, evolution, and mechanism of action of insulin receptors (IR). INS, insulin-like growth factor (IGF)-1, and IGF-2 share a common ancestor; INS and a single IGF occur in Agnathans, whereas INS and distinct IGF-1 and IGF-2s appear in Chondrichthyes. Some but not all teleost fish possess multiple INS genes, but it is not clear if they arose from a common gene duplication event or from multiple separate gene duplications. INS is produced by the endocrine pancreas of fish as well as by several other tissues, including brain, pituitary, gastrointestinal tract, and adipose tissue. INS regulates various aspects of feeding, growth, development, and intermediary metabolism in fish. The actions of INS are mediated through the insulin receptor (IR), a member of the receptor tyrosine kinase family. IRs are widely distributed in peripheral tissues of fish, and multiple IR subtypes that derive from distinct mRNAs have been described. The IRs of fish link to several cellular effector systems, including the ERK and IRS-PI3k-Akt pathways. The diverse effects of INS can be modulated by altering the production and release of INS as well as by adjusting the production/surface expression of IR. The diverse actions of INS in fish as well as the diverse nature of the neural, hormonal, and environmental factors known to affect the INS signaling system reflects the various life history patterns that have evolved to enable fish to occupy a wide range of aquatic habitats.

Cloning and molecular characterization of the glucose transporter 1 in tilapia (Oreochromis niloticus)

Facilitative glucose transporters (GLUTs) are responsible for passively transporting monosaccharides across the plasma membrane. We sequenced and characterized the Nile tilapia (Oreochromis niloticus) GLUT-1 (tGLUT-1) cDNA and genomic DNA. Using rapid amplification of the cDNA ends (RACE), two tGLUT-1 transcripts were detected differing in the length of the 3' untranslated region, 2851 and 4577 bp. Translated tGLUT-1 is a 490 amino acid product, which shares 74% homology with that of humans. Computer analysis of the amino acid sequence predicted 12 transmembrane domains, which are conserved in the GLUT-1 of various species. The tGLUT-1 gene spans more than 11 kb, and similar to the mammalian GLUT-1 genes has a 10 exon, 9 intron organization. Potential promoter regulatory elements have some similarity to those recorded for human, mouse, and rat GLUT-1 genes. Tissue expression studies revealed both GLUT-1 transcripts in liver, Brockmann bodies (BB), heart, small intestine, adipose tissue, white and red muscle, gill, spleen, pituitary gland, and brain. The highest level of expression was detected in tilapia heart, followed by BB, brain, and muscle. Protein based food and glucose had minor or no effects on the level of tGLUT-1 expression in most tissues. The tGLUT-1 mRNA level was significantly induced by glucose and food only in white muscle. Current results suggest that tGLUT-1 is similar to the GLUT-1 of other teleost species and mammals at the genomic, mRNA, and amino acid levels, supporting the concept that tGLUT-1 functions as a ubiquitous basal level glucose transporter.

Regulation of insulin gene expression and insulin production in Nile tilapia (Oreochromis niloticus)

Compared to mammals, little is known about insulin gene expression in fish. Using transient transfection experiments and mammalian insulinoma cell lines we demonstrate that transcription of the Nile tilapia (Oreochromis niloticus) insulin gene is (a) regulated in a beta-cell-specific manner; and (b) not sensitive to the glucose stimulations. Deletion analysis of the 1575 bp 5' insulin gene flanking sequence revealed that cooperative interactions between regulatory elements within the proximal (-1 to -396 bp) and the distal (-396 bp to -1575 bp) promoter regions were necessary for induction of the beta-cell-specific transcription. Effects of glucose and arginine on endogenous insulin secretion, translation, and transcription in isolated tilapia Brockmann bodies were determined using Northern hybridization, Western analysis, and quantitative RT-PCR. Similar to the regulation of mammalian insulin, we found that increases of glucose (1-70 mM) and arginine (0.4-25 mM) induced insulin secretion. However, transcription of the insulin gene was activated only by extremely high concentrations of glucose and arginine added simultaneously. When stimulated for 24 h with low concentrations of both inducers or with either of them added separately, tilapia beta-cells were able to replenish secreted insulin and to maintain insulin stores at a constant level without elevations of the insulin mRNA levels. Since the basal level of insulin mRNA was approximately 3.7-fold higher in tilapia beta-cells than it is in mammalian beta-cells, insulin production in tilapia cells probably relies on an enlarged intracellular insulin mRNA pool and does not require the transcriptional activation of the insulin gene.

Things we have learned from tilapia islet xenotransplantation

An islet xenotransplantation model has been developed using tilapia (Oreochromis niloticus) as the donors. Studies using this model for the treatment of experimental type 1 diabetes in mice have produced promising results including the maintenance of long-term normoglycemia and mammalian-like glucose tolerance profiles in islet graft recipients. Islet encapsulation has also provided a promising method for the prevention of graft rejection, and strains of transgenic tilapia expressing a [desThrB30] human insulin molecule have been produced. In addition to studying islet transplantation for the treatment of type 1 diabetes, these studies have also produced insights into piscine glucose homeostasis. Studies demonstrating the glucose responsiveness of tilapia islets are described. In addition, work performed by our group and by others pertaining to presence and nature of piscine glucose transporters is reviewed. Finally, studies addressing some of the broader challenges of islet xenotransplantation are discussed with particular attention paid to the post-transplantation fate of the various islet cell populations and the proteins they produce.

Development of the islets, exocrine pancreas, and related ducts in the Nile tilapia, Oreochromis niloticus (Pisces: Cichlidae)

Pancreatic development and the relationship of the islets with the pancreatic, hepatic, and bile ducts were studied in the Nile tilapia, Oreochromis niloticus, from hatching to the onset of maturity at 7 months. The number of islets formed during development was counted, using either serial sections or dithizone staining of isolated islets. There was a general increase in islet number with both age and size. Tilapia housed in individual tanks grew more quickly and had more islets than siblings of the same age left in crowded conditions. The pancreas is a compact organ in early development, and at 1 day posthatch (dph) a single principal islet, positive for all hormones tested (insulin, SST-14, SST-28, glucagon, and PYY), is partially surrounded by exocrine pancreas. However, the exocrine pancreas becomes more disseminated in older fish, following blood vessels along the mesenteries and entering the liver to form a hepatopancreas. The epithelium of the pancreatic duct system from the intercalated ducts to the main duct entering the duodenum was positive for glucagon and SST-14 in 8 and 16 dph tilapia. Individual insulin-immunopositive cells were found in one specimen. At this early stage in development, therefore, the pancreatic duct epithelial cells appear to be pluripotent and may give rise to the small islets found near the pancreatic ducts in 16-37 dph tilapia. Glucagon, SST-14, and some PPY-positive enteroendocrine cells were present in the intestine of the 8 dph larva and in the first part of the intestine of the 16 dph juvenile. Glucagon and SST-14-positive inclusions were found in the apical cytoplasm of the mid-gut epithelium of the 16 dph tilapia. These hormones may have been absorbed from the gut lumen, since they are produced in both the pancreatic ducts and the enteroendocrine cells. At least three hepatic ducts join the cystic duct to form the bile duct, which runs alongside the pancreatic duct to the duodenum.