Things we have learned from tilapia islet xenotransplantation

Molecular and metabolic adaption of glucose metabolism in the red and white muscle of the omnivorous GIFT tilapia Oreochromis niloticus to a glucose load

In this experiment, Genetically improved farmed Nile tilapia Oreochromis niloticus were intraperitoneally injected with 1 g glucose/kg of body weight or saline. Red and white muscle tissues were collected at 0, 1, 2, 4, 6 and 12 h after the glucose tolerance test (GTT) or saline injection, and the time course of changes in molecular and metabolic adaption of glucose metabolism of these two tissues were evaluated. The results showed that the expression of insulin-responsive glucose transporter 4 (glut4) was up-regulated at 4 h after the GTT in the red muscle, implying an increase of glucose uptake. However, the expression of glut4 in the white muscle did not change with glucose load. The glycolysis of red muscle in tilapia was stimulated during 2-4 h after the GTT, as the expression of hexokinase 1b (hk1b), hk2, phosphofructokinase muscle type a (pfkma) and pfkmb and the activity of HK and PFK increased. By contrast, only the expression of hk1b was up-regulated at 6 h after the GTT in the white muscle. The mRNA level of glycogen synthase 1 (gys1) and glycogen content increased at 2 and 6 h, respectively after the GTT in the red muscle, suggesting that glucose storage was provoked. However, glycogen content in the white muscle was not impacted by GTT. Lipogenesis was stimulated in the red muscle as reflected by up-regulated expression of acetyl-CoA carboxylase α (accα) (during 2-4 h) and accβ (during 4-12 h) with GTT. In the white muscle, however, the expression of accα was not changed, and mRNA level of accβ was not up-regulated until 6 h after the GTT. Taken together, it was concluded that the glycolytic and glycogen synthesis mechanisms in the red muscle were highly regulated by an acute glucose load while those in the white muscle were less responsive to this stimulus.

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.

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.

Targeting zebrafish and murine pituitary corticotroph tumors with a cyclin-dependent kinase (CDK) inhibitor

Cushing disease caused by adrenocorticotropin (ACTH)-secreting pituitary adenomas leads to hypercortisolemia predisposing to diabetes, hypertension, osteoporosis, central obesity, cardiovascular morbidity, and increased mortality. There is no effective pituitary targeted pharmacotherapy for Cushing disease. Here, we generated germline transgenic zebrafish with overexpression of pituitary tumor transforming gene (PTTG/securin) targeted to the adenohypophyseal proopiomelanocortin (POMC) lineage, which recapitulated early features pathognomonic of corticotroph adenomas, including corticotroph expansion and partial glucocorticoid resistance. Adult Tg:Pomc-Pttg fish develop neoplastic coticotrophs and pituitary cyclin E up-regulation, as well as metabolic disturbances mimicking hypercortisolism caused by Cushing disease. Early development of corticotroph pathologies in Tg:Pomc-Pttg embryos facilitated drug testing in vivo. We identified a pharmacologic CDK2/cyclin E inhibitor, R-roscovitine (seliciclib; CYC202), which specifically reversed corticotroph expansion in live Tg:Pomc-Pttg embryos. We further validated that orally administered R-roscovitine suppresses ACTH and corticosterone levels, and also restrained tumor growth in a mouse model of ACTH-secreting pituitary adenomas. Molecular analyses in vitro and in vivo showed that R-roscovitine suppresses ACTH expression, induces corticotroph tumor cell senescence and cell cycle exit by up-regulating p27, p21 and p57, and downregulates cyclin E expression. The results suggest that use of selective CDK inhibitors could effectively target corticotroph tumor growth and hormone secretion.

Derivation and characterization of embryonic stem-like cells of Indian major carp Catla catla

Embryonic stem (ES)-like cells were derived from mid-blastula stage embryos of a freshwater fish, catla Catla catla, under feeder-free condition and designated as CCES cells. The conditioned media was optimized with 10% foetal bovine serum (FBS), fish embryo extract (FEE) having 100 µg ml(-1) protein concentration, 15 ng ml(-1) basic fibroblast growth factor (bFGF) and basic media containing Leibovitz-15, DMEM with 4·5 g l(-1) glucose and Ham's F12 (LDF) in 2:1:1 ratio using a primary culture of CCES cells. Cells attached to gelatin-coated plates after 24 h of seeding and ES-like colonies were obtained at day 5 onwards. A stable cell culture was obtained after passage 10 and further maintained up to passage 44. These cells were characterized by their typical morphology, high alkaline phosphatase activity, positive expression of cell-surface antigen SSEA-1, transcription factor Oct4, germ cell marker vasa and consistent karyotype up to extended periods. The undifferentiated state was confirmed by their ability to form embryoid bodies and their differentiation potential.

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.

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.

The fish endocrine pancreas: review, new data, and future research directions in ontogeny and phylogeny

The literature on the ontogeny and phylogeny of the endocrine pancreas of ray-finned fishes is summarized since the latest review in fish [Youson, J.H., Al-Mahrouki, A.A., 1999. Review. Ontogenetic and phylogenetic development of the endocrine pancreas (islet organ) in fishes. Gen. Comp. Endocrinol. 116, 303-335]. A basic description and a demonstration of the diversity of the fish islet organ is provided through new immunohistochemical data on islet tissue from a basal teleost, an osteoglossomorph, and a more derived teleost, a perciforme. Unlike the previous review, the present report provides a review and discussion of the utility of sequence data of insulin, somatostatin, and NPY- and glucagon-family peptides in phylogenetic analyses of jawed and jawless fishes. The present study also provides the first comparative analysis of sequences of preprohormones of endocrine peptides from closely related basal teleost species. Some nucleotide and deduced amino acid sequence data for preprosomatostatins (PPSS-I and/or -II) are compared for four species of bonytongues, Osteoglossomorpha, and with PPSSs of the white sucker, Catostomus commersoni, representing Cypriniformes, a more generalized teleost order. Phylogenetic analysis of deduced amino acid sequences of the PPSSs of these species and others from databases indicates good support for the monophyly of Osteoglossomorpha and some support for the present taxonomic grouping of the osteoglossomorphs examined, and also the white sucker. However, PPSS may have limited phylogenetic utility due to the relative short sequence, particularly in resolving relationships among lineages that diverged over a short period of time. Since in the few fish species examined we have just touched the surface in describing the diversity of structure of the islet organ, and likely the nature of the products of its cells, this report promotes the continued study of this organ.