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.

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.

Polarization of endosomal SNX27 in migrating and tumor-engaged Natural Killer cells

Polarization is a critical mechanism for the proper functioning of many cell types. For lymphocytes, it is essential in a variety of processes, including migration from the blood to other tissue sites and vice versa. In NK cells and CTLs, the cytotoxic granule delivery mechanism requires polarization for granule movement to the immunological synapse (IS), in killing tumor and virus-infected cells. Recently, it has become apparent that endosomes are also involved in the cytotoxic mechanism. Using an in vitro conjugation approach, we show that in NK-92 cells, endosomal Sorting Nexin 27 (SNX27) polarizes to the IS during tumor cell engagement in a distinct compartment adjacent to the cytotoxic granules. We also show that SNX27 polarizes to the apical membrane, opposite the uropod, during NK cell migration. These previously unreported results indicate that SNX27 is a participant in NK cell polarization, as a mediator or target of the mechanism.

Sorting nexin 27 interacts with the Cytohesin associated scaffolding protein (CASP) in lymphocytes

CASP is a small cytokine-inducible protein, primarily expressed in hematopoetic cells, which associates with members of the Cytohesin/ARNO family of guanine nucleotide-exchange factors. Cytohesins activate ARFs, a group of GTPases involved in vesicular initiation. Functionally, CASP is an adaptor protein containing a PDZ domain, a coiled-coil, and a potential carboxy terminal PDZ-binding motif that we sought to characterize here. Using GST pulldowns and mass spectrometry we identified the novel interaction of CASP and sorting nexin 27 (SNX27). In lymphocytes, CASP's PDZ-binding motif interacts with the PDZ domain of SNX27. This protein is a unique member of the sorting nexin family of proteins, a group generally involved in the endocytic and intracellular sorting machinery. Endogenous SNX27 and CASP co-localize at the early endosomal compartment in lymphocytes and also in transfection studies. These results suggest that endosomal SNX27 may recruit CASP to orchestrate intracellular trafficking and/or signaling complexes.

Rejection of large HPV-16 expressing tumors in aged mice by a single immunization of VacciMax encapsulated CTL/T helper peptides

The incidence of cancer increases significantly in later life, yet few pre-clinical studies of cancer immunotherapy use mice of advanced age. A novel vaccine delivery platform (VacciMax,VM) is described that encapsulates antigens and adjuvants in multilamellar liposomes in a water-in-oil emulsion. The therapeutic potential of VM-based vaccines administered as a single dose was tested in HLA-A2 transgenic mice of advanced age (48-58 weeks old) bearing large palpable TC1/A2 tumors. The VM-based vaccines contained one or more peptides having human CTL epitopes derived from HPV 16 E6 and E7. VM formulations contained a single peptide, a mixture of four peptides or the same four peptides linked together in a single long peptide. All VM formulations contained PADRE and CpG as adjuvants and ISA51 as the hydrophobic component of the water-in-oil emulsion. VM-formulated vaccines containing the four peptides as a mixture or linked together in one long peptide eradicated 19-day old established tumors within 21 days of immunization. Peptide-specific cytotoxic cellular responses were confirmed by ELISPOT and intracellular staining for IFN-gamma producing CD8+ T cells. Mice rendered tumor-free by vaccination were re-challenged in the opposite flank with 10 million HLF-16 tumor cells, another HLA-A2/E6/E7 expressing tumor cell line. None of these mice developed tumors following the re-challenge. In summary, this report describes a VM-formulated therapeutic vaccine with the following unprecedented outcome: a) eradication of large tumors (> 700 mm3) b) in mice of advanced age c) in less than three weeks post-immunization d) following a single vaccination.

Therapy of established B16-F10 melanoma tumors by a single vaccination of CTL/T helper peptides in VacciMax

BACKGROUND

Melanoma tumors are known to express antigens that usually induce weak immune responses of short duration. Expression of both tumor-associated antigens p53 and TRP2 by melanoma cells raises the possibility of simultaneously targeting more than one antigen in a therapeutic vaccine. In this report, we show that VacciMax (VM), a novel liposome-based vaccine delivery platform, can increase the immunogenicity of melanoma associated antigens, resulting in tumor elimination.

METHODS

C57BL/6 mice bearing B16-F10 melanoma tumors were vaccinated subcutaneously 6 days post tumor implantation with a mixture of synthetic peptides (modified p53: 232-240, TRP-2: 181-188 and PADRE) and CpG. Tumor growth was monitored and antigen-specific splenocyte responses were assayed by ELISPOT.

RESULTS

Vaccine formulated in VM increased the number of both TRP2- and p53-specific IFN-gamma producing splenocytes following a single vaccination. Vaccine formulated without VM resulted only in enhanced IFN-gamma producing splenocytes to one CTL epitopes (TRP2:180-188), suggesting that VM overcomes antigen dominance and enhances immunogenicity of multiple epitopes. Vaccination of mice bearing 6-day old B16-F10 tumors with both TRP2 and p53-peptides formulated in VM successfully eradicated tumors in all mice. A control vaccine which contained all ingredients except liposomes resulted in eradication of tumors in no more than 20% of mice.

CONCLUSION

A single administration of VM is capable of inducing an effective CTL response to multiple tumor-associated antigens. The responses generated were able to reject 6-day old B16-F10 tumors.

Insulin expression in the brain and pituitary cells of tilapia (Oreochromis niloticus)

While the presence of immunoreactive insulin in the central nervous system of many vertebrate species is well known, the origin of brain insulin is still debated. In this study, we applied RT-PCR, quantitative RT-PCR (qRT-PCR), and Northern hybridization to examine expression of the insulin gene in different tissues of an adult teleost fish, the Nile Tilapia (Oreochromis niloticus). We found that the insulin gene is transcribed at a high level in Brockmann bodies (pancreatic islet organs) and at a low level in the brain and pituitary gland. In the brain, insulin transcripts were detected in all areas by qRT-PCR and in situ hybridization. The highest level of insulin mRNA was found in the hypothalamus. The level of insulin transcription in the pituitary gland was 6-fold higher than that in the brain and 4.6-fold higher than that in the hypothalamus. Furthermore, insulin mRNA and immunoreactive insulin-like protein was detected in the pituitary gland using in situ hybridization, immunohistochemistry, and Western blot analysis. Our results indicate that in adult tilapia insulin expression is not restricted to the endocrine pancreatic cells, but also occurs in endocrine cells of the pituitary gland and in the neuronal cells of the brain, suggesting that the brain/pituitary gland might represent extrapancreatic origin of insulin production.

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.

Eradication of established HPV 16-expressing tumors by a single administration of a vaccine composed of a liposome-encapsulated CTL-T helper fusion peptide in a water-in-oil emulsion

Human papillomavirus (HPV)-induced cervical cancer is the second most common cancer among women worldwide with half a million new cases per year. Despite the encouraging development of a preventive vaccine for HPV, a therapeutic vaccine for cervical cancer or pre-cancerous lesions remains a high priority. The preclinical study reported here used VacciMax((R)) (VM) to deliver a peptide-based vaccine composed of an HPV 16 E7-derived cytotoxic T lymphocyte (CTL) epitope fused to the T helper epitope PADRE (FP) and combined with CpG or lipopeptide adjuvant. In the study, C57BL/6 mice received 0.5million HPV 16-expressing C3 tumor cells. Mice were inoculated post-tumor challenge with a single s.c. injection of FP-CpG-VM on either day 4, 5, 6, 9, or 14. All mice that received the FP-CpG-VM vaccine were tumor-free to day 130 when the experiment was terminated. In contrast, only a minority of mice that received a control vaccine were tumor-free on day 60. Cytotoxicity assays, ELISPOT and intracellular staining for interferon (IFN)-gamma showed the immune response was specific for the selected CTL epitope. All mice that received the FP-CpG-VM vaccine remained tumor-free when re-challenged with 6million C3 cells. Cytotoxicity assays 4 months post-challenge showed that only splenocytes from mice inoculated with the FP-CpG-VM vaccine had high lysis activity. These results indicate that VacciMax((R)) causes a rapid, robust, durable and therapeutic CTL response to HPV 16 E7 protein expressing tumors.

Survey of zona pellucida antigens for immunocontraception of cats

The purpose of this study was to screen a panel of native zona pellucida (ZP) antigens isolated from five mammalian species for immunocontraceptive activity in the cat (Felis catus). Native soluble-isolated ZP (SIZP) was prepared from the ovaries of cows (bZP), cats (fZP), ferrets (feZP), dogs (cZP), and mink (mZP). Vaccines were constructed using SIZP from each of the above species encapsulated in liposomes suspended in saline and emulsified with Freund's complete adjuvant (SpayVac). Female cats were immunized once (n = 3 cats per group). Serum was collected for determination of antibody titers against SIZP and for binding of antibodies to feline ovaries. All cats responded to immunization by producing anti-SIZP antibodies. The most immunogenic SIZP in cats was from mink, followed by feZP, cZP, and fZP in descending order. Antibodies had low reactivity for fZP, and no reactivity against feline ovaries was detected by immunohistochemistry. A breeding trial was commenced 20 weeks after immunization. All cats became pregnant, averaging 4.1 +/- 0.7 viable kittens per litter. We have previously shown that porcine SIZP is not an effective antigen for immunocontraception of cats. In this study, SIZP from five other mammalian species were immunogenic in the cat, but ZP antibodies failed to bind to fZP in situ, and fertility was not impeded.

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

BACKGROUND

Tilapia are commercially important tropical fish which, like many teleosts, have anatomically discrete islet organs called Brockmann bodies. When transplanted into diabetic nude mice, tilapia islets provide long-term normoglycemia and mammalian-like glucose tolerance profiles.

METHODS

Using site-directed mutagenesis and linker ligation we have "humanized" the tilapia insulin gene so that it codes for [desThrB30] human insulin while maintaining the tilapia regulatory sequences. Following microinjection into fertilized eggs, we screened DNA isolated from whole fry shortly after hatching by PCR. Positive fish were grown to sexual maturity and mated to wild-types and positive Fl's were further characterized.

RESULTS

Human insulin was detected in both serum and in the clusters of beta cells scattered throughout the Brockmann bodies. Surrounding non-beta cells as well as other tissues were negative indicating beta cell specific expression. Purification and sequencing of both A-and B-chains verified that the insulin was properly processed and humanized.

CONCLUSIONS

After extensive characterization, transgenic tilapia could become a suitable, inexpensive source of islet tissue that can be easily mass-produced for clinical islet xenotransplantation. Because tilapia islets are exceedingly resistant to hypoxia by mammalian standards, transgenic tilapia islets should be ideal for xenotransplantation using immunoisolation techniques.

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.

Piscine Islet Xenotransplantation

Tilapia, a teleost fish species with large anatomically discrete islet organs (Brockmann bodies; BBs) that can be easily harvested without expensive and fickle islet isolation procedures, make an excellent donor species for experimental islet xenotransplantation research. When transplanted into streptozotocin-diabetic nude or severe combined immunodeficient mice, BBs provide long-term normoglycemia and mammalian-like glucose tolerance profiles. However, when transplanted into euthymic recipients, the mechanism of islet xenograft rejection appears very similar to that of islets from "large animal" donor species such as the very popular fetal/neonatal porcine islet cell clusters (ICCs). Tilapia islets are more versatile than ICCs and can be transplanted (1) into the renal subcapsular space, the cryptorchid or noncryptorchid testis, or intraportally as neovascularized cell transplants; (2) as directly vascularized organ transplants; or (3) intraperitoneally after microencapsulation. Unlike the popular porcine ICCs, BBs function immediately after transplantation; thus, their rejection can be assessed on the basis of loss of function as well as other parameters. We have also shown that transplantation of tilapia BBs into nude mice can be used to study the possible implications of cross-species physiological incompatibilities in xenotransplantation. Unfortunately, tilapia BBs might be unsuitable for clinical islet xenotransplantation because tilapia insulin differs from human insulin by 17 amino acids and, thus, would be immunogenic and less biologically active in humans. Therefore, we have produced transgenic tilapia that express a "humanized" tilapia insulin gene. Future improvements on these transgenic fish may allow tilapia to play an important role in clinical islet xenotransplantation.

The N-terminal coiled coil domain of the cytohesin/ARNO family of guanine nucleotide exchange factors interacts with the scaffolding protein CASP

Cytohesin is a guanine nucleotide exchange factor that regulates members of the ADP-ribosylation factor (ARF) family of small GTPases. All of the members of the cytohesin family (including ARNO, ARNO3, and the newly characterized cytohesin-4) have a similar domain distribution consisting of a Sec7 homology domain, a pleckstrin homology domain, and an N-terminal coiled coil. In this study, we attempt to identify proteins that interact specifically with the coiled coil motif of cytohesin. Yeast two-hybrid screening of a B cell library using the cytohesin N terminus as bait, identified CASP, a scaffolding protein of previously unknown function, as a binding partner. CASP contains an internal coiled coil motif that is required for cytohesin binding both in vitro and in COS-1 cells. The specificity of the coiled coil of CASP is not restricted to cytohesin, however, because it is also capable of interacting with other members of the cytohesin/ARNO family, ARNO and ARNO3. In immunofluorescence experiments, CASP localizes to perinuclear tubulovesicular structures that are in close proximity to the Golgi. These structures remain relatively undisturbed when the cells are treated with brefeldin A. In epidermal growth factor-stimulated COS-1 cells overexpressing cytohesin and CASP, cytohesin recruits CASP to membrane ruffles, revealing a functional interaction between the two proteins. These observations collectively suggest that CASP is a scaffolding protein that facilitates the function of at least one member of the cytohesin/ARNO family in response to specific cellular stimuli.

Cell therapy for diabetes using piscine islet tissue

The islet tissue, called Brockmann bodies, in certain teleost fish is anatomically distinct from the pancreatic exocrine tissue and can be easily identified macroscopically. Expensive islet isolation procedures, such as required when procuring islet tissue from mammalian pancreases, are unnecessary. Tilapia islets transplanted into diabetic athymic nude mice will produce long-term normoglycemia and mammalian-like glucose tolerance profiles. Encapsulated tilapia islets function well after transplantation into euthymic recipients. Additionally, tilapia are potentially ideal xenogeneic donors because of markedly lower donor production costs, minimal islet procurement costs, and possibly decreased xenozoonotic potential relative to mammalian donors. Tilapia islets appear to be appropriately glucose responsive with high insulin output, can be cryopreserved, and are much more resistant to hypoxia than mammalian islets. Because tilapia and human insulin differ by 17 amino acids, we have cloned, sequenced, and modified the tilapia insulin gene by site-directed mutagenesis resulting in a tilapia insulin gene that codes for "humanized" insulin while still maintaining all of the tilapia regulatory (noncoding) sequences. We have now produced small numbers of founder transgenic tilapia with incorporation of our humanized tilapia insulin gene construct, and we have shown transmission and expression of the transgene in the beta cells and serum of their Fl offspring. Our ultimate goal is to achieve homologous recombination and to breed for homozygosity for the hybrid insulin gene. Subsequent generations of transgenic tilapia will undergo a program of genomic optimization selecting for growth, survival, and fecundity as well as stability of the transgene. Islets from the resulting transgenic fish, after extensive characterization, could be harvested, encapsulated, and then transplanted into diabetic patients.

PNRC: a proline-rich nuclear receptor coregulatory protein that modulates transcriptional activation of multiple nuclear receptors including orphan receptors SF1 (steroidogenic factor 1) and ERRalpha1 (estrogen related receptor alpha-1)

PNRC (proline-rich nuclear receptor coregulatory protein) was identified using bovine SF1 (steroidogenic factor 1) as the bait in a yeast two-hybrid screening of a human mammary gland cDNA expression library. PNRC is unique in that it has a molecular mass of 35 kDa, significantly smaller than most of the coregulatory proteins reported so far, and it is proline-rich. PNRC's nuclear localization was demonstrated by immunofluorescence and Western blot analyses. In the yeast two-hybrid assays, PNRC interacted with the orphan receptors SF1 and ERRalpha1 in a ligand-independent manner. PNRC was also found to interact with the ligand-binding domains of all the nuclear receptors tested including estrogen receptor (ER), androgen receptor (AR), glucocorticoid receptor (GR), progesterone receptor (PR), thyroid hormone receptor (TR), retinoic acid receptor (RAR), and retinoid X receptor (RXR) in a ligand-dependent manner. Functional AF2 domain is required for nuclear receptors to bind to PNRC. Furthermore, in vitro glutathione-S-transferase pull-down assay was performed to demonstrate a direct contact between PNRC and nuclear receptors such as SF1. Coimmunoprecipitation experiment using Hela cells that express PNRC and ER was performed to confirm the interaction of PNRC and nuclear receptors in vivo in a ligand-dependent manner. PNRC was found to function as a coactivator to enhance the transcriptional activation mediated by SF1, ERR1 (estrogen related receptor alpha-1), PR, and TR. By examining a series of deletion mutants of PNRC using the yeast two-hybrid assay, a 23-amino acid (aa) sequence in the carboxy-terminal region, aa 278-300, was shown to be critical and sufficient for the interaction with nuclear receptors. This region is proline rich and contains a SH3-binding motif, S-D-P-P-S-P-S. Results from the mutagenesis study demonstrated that the two conserved proline (P) residues in this motif are crucial for PNRC to interact with the nuclear receptors. The exact 23-amino acid sequence was also found in another protein isolated from the same yeast two-hybrid screening study. These two proteins belong to a new family of nuclear receptor coregulatory proteins.

N-terminal targeting of guanine nucleotide exchange factors (GEF) for ADP ribosylation factors (ARF) to the Golgi

B2-1 (cytohesin-1) is a member of a group of proteins (including ARNO and ARNO3) that are all of similar size and domain composition. The three proteins contain an N-terminal coiled-coil domain, followed by a Sec7 and a pleckstrin homology (PH) domain. While it is well established that the Sec7 domain functions as a guanine nucleotide exchange factor (GEF) for ADP-ribosylation factors (ARFs) and the PH domain anchors the proteins to membrane phosphoinositols, the function of the N-terminal domain is unknown. Here we show that the N terminus of B2-1 (residues 1–54) is necessary and sufficient to target the protein to the Golgi. The Sec7+PH domains of B2-1 (residues 55–398) are not sufficient for Golgi localization. Further deletion analysis and point mutagenesis indicate that the coiled-coil domain within the N terminus is responsible for Golgi targeting. Furthermore, ARNO and ARNO3 N termini also have the same capability of targeting to the Golgi. We conclude that the N-terminal, (α)-helical, coiled-coil domain is used to target this family of proteins to the Golgi complex.

B2-1, a Sec7- and pleckstrin homology domain-containing protein, localizes to the Golgi complex

B2-1 is a human protein that contains both a Sec7 and a pleckstrin homology domain. The yeast Sec7 protein was previously shown to be involved in vesicle formation in the Golgi and endoplasmic reticulum. Recently, several groups have shown that B2-1 and highly similar proteins (e.g., ARNO, ARNO3) have varied cellular functions and subcellular locations. One of these is an association of the B2-1 Sec7 domain with the plasma membrane, binding to the cytoplasmic portion of the integrin beta2 chain (CD18) and is postulated to be involved in inside-out signaling. Other groups have shown that B2-1 and these related proteins are guanine nucleotide-exchange factors that act upon ADP ribosylation factors (ARFs) and are localized to the Golgi or plasma membrane. Here we report the subcellular localization of B2-1 protein. Interestingly, B2-1 does not localize to the plasma membrane but rather associates with a distinct Golgi complex compartment. B2-1's distribution can be disrupted by brefeldin A, a drug that rapidly disrupts the Golgi apparatus by inhibiting ARF activity. Furthermore, transient transfection of GFP-tagged B2-1 shows Golgi complex targeting. Excessive overexpression of transfected B2-1 causes partial Golgi dispersion.

Cloning, sequencing and characterization of the tilapia insulin gene

Using degenerate primers based on insulin sequences from other organisms, we report the cloning of the complete tilapia (Oreochromis niloticus) insulin gene. Using nested primers and a cassette ligation strategy we have also cloned 932 base pairs (bp) of 5' flanking and 1152 bp of 3' flanking sequence. The tilapia insulin gene has the similar three exon (one untranslated), two intron distribution found in all insulin genes sequenced to date. However, intron 1 is unique in having a smaller size (73 bp) than found in other organisms. 5' RNA extension revealed the presence of two potential transcriptional start sites. A perfect TATA box is located at -30 bp from the first transcriptional start site. Interestingly, the 5' upstream region contains a microsatellite close to the same position of a unique minisatellite found only in humans and primates. The upstream region also contains several potential control elements to regulate insulin expression that are found in mammalian insulin genes.

Expression and temperature-dependent regulation of the beta2-microglobulin (Cyca-B2m) gene in a cold-blooded vertebrate, the common carp (Cyprinus carpio L.)

Expression of beta2-microglobulin (beta2m) in the common carp was studied using a polyclonal antibody raised against a recombinant protein obtained from eukaryotic expression of the Cyca-B2m gene. Beta2m is expressed on peripheral blood Ig+ and Ig lymphocytes, but not on erythrocytes and thrombocytes. In spleen and pronephros, dull- and bright-positive populations could be identified correlating with the presence of erythrocytes, thrombocytes, and mature leucocytes or immature and mature cells from the lympho-myeloid lineage, respectively. Thymocytes were shown to be comprised of a single bright-positive population. The Cyca-B2m polyclonal antiserum was used in conjunction with a similarly produced polyclonal antiserum to an MHC class I (Cyca-UA) alpha chain to investigate the expression of class I molecules on peripheral blood leucocytes (PBL) at different permissive temperatures. At 12 degrees C, a temporary downregulation of class I molecules was demonstrated, which recovered to normal levels within 3 days. However, at 6 degrees C, a lasting absence of class I cell-surface expression was observed, which could be restored slowly by transfer to 12 degrees C. The expression of immunoglobulin molecules on B cells was unaffected by temperature changes. The absence of the class I cell-surface expression was shown to be the result of a lack of sufficient Cyca-B2m gene transcription, although Cyca-UA mRNA was present at comparable levels at all temperatures. This suggests that class I expression is regulated by a temperature-sensitive transcription of the Cyca-B2m gene.

Evidence for a long-lasting single administration contraceptive vaccine in wild grey seals

A single-administration birth control vaccine based on liposome delivery of porcine zona pellucida antigens reduced pup production in grey seals (Halichoerus grypus) by about 90%. Anti-porcine zona pellucida titers of individual seals with two or more recaptures were variable but without a diminishing trend during the 5 year post-immunization period. Seals that produced at least one or more pups during the 2-5 year post-immunization period when the vaccine is fully effective, had an average anti-porcine zona pellucida titer of 5% of the reference serum. In contrast, the subset of seals that did not reproduce but were recaptured during the breeding season had an average titer of 31% of the reference serum. As measured by antibody titers and pup production, there were no differences in efficacy of the vaccine in 14-, 20- and 21-year-old female grey seals.

Temporal trends in antibody production in captive grey, harp and hooded seals to a single administration immunocontraceptive vaccine

The temporal production of antibody to a single-administration immunocontraceptive vaccine, known to be immunocontraceptive in free-ranging female grey seals (Halichoerus grypus), was studied in captive grey seals, harp seals (Phoca groenlandica) and hooded seals (Cystophora cristata). The vaccine is based on liposome delivery of porcine zona pellucida antigens. When measured by antigen capture, the response of hooded and harp seals to the vaccine was similar to the response of grey seals. Determination of antibody production by ELISA with protein A, ELISA with rabbit anti-seal immunoglobulin sera and SDS-PAGE after affinity chromatography confirmed the similarity in response to the vaccine by grey and harp seals, but suggested lower titers in hooded seals. The vaccine produced titers in captive, juvenile grey and harp seals known to be immunocontraceptive in wild, adult grey seals.

Cloning a cDNA from human NK/T cells which codes for a protein with high proline content

A cDNA clone, B4-2, was isolated from a natural killer (NK) minus T cell subtractive library. The B4-2 clone coded for an mRNA of 2061 bp in length. It encodes a deduced 327 aa protein with a calculated molecular mass of 35.2 kDa. Searching of B4-2 DNA and protein sequences against various databases revealed no high homology to other sequences. However, B4-2 has an unusually high proline content (13%), contains a putative nuclear targeting sequence, and has several SPXX motifs which are frequently found in gene regulatory proteins. One of the stretches of prolines in B4-2 closely resembles the ligand for proteins with SH3 domains. Northern hybridization data showed that B4-2 is not a lymphoid specific gene and is expressed in a hepatoma cell line and also weakly transcribed or absent in a variety of other cells. A polyclonal antiserum raised against recombinant B4-2 recognizes a 32-34 kDa protein in lymphocytes.

Cloning a cDNA from human NK/T cells which codes for an unusual leucine zipper containing protein

A 1724 base pair (bp) clone, B3-1, was obtained from a human NK subtracted cDNA library and sequenced. The cDNA encoded a 324 amino acid protein with a calculated molecular mass of 36 kDa. The deduced protein did not contain any hydrophobic domains, suggesting that it was not secreted or membrane bound. Extensive database searches showed no significant overall homology to any known proteins or genes. The protein did, however, contain an unusually long (twice normal) leucine zipper and the nuclear targeting sequence found in many transcription factors and oncogenes. The cDNA also contained three repeats of the sequence 'ATTTA' in its 3' untranslated region, a motif associated with many oncogenes, transcription factors and interleukins. The mRNA for this gene is weakly expressed in resting NK/T cells.

Adventitious variability? The amino acid sequences of nonvertebrate globins

1. The more than 140 amino acid sequences of non-vertebrate hemoglobins (Hbs) and myoglobins (Mbs) that are known at present, can be divided into several distinct groups: (1) single-chain globins, containing one heme-binding domain; (2) truncated, single-chain, one-domain globins; (3) chimeric, one-domain globins; (4) chimeric, two-domain globins; and (5) chimeric multi-domain globins. 2. The crystal structures of eight nonvertebrate Hbs and Mbs are known, all of them monomeric, one-domain globin chains. Although these molecules represent plants, prokaryotes and several metazoan groups, and although the inter-subunit interactions in the dimeric and tetrameric molecules differ from the ones observed in vertebrate Hbs, the secondary structures of all seven one-domain globins retain the characteristic vertebrate "myoglobin fold". No crystal structures of globins representing the other four groups have been determined. 3. Furthermore, a number of the one-, two- and multi-domain globin chains participate in a broad variety of quaternary structures, ranging from homo- and heterodimers to highly complex, multisubunit aggregates with M(r) > 3000 kDa (S. N. Vinogradov, Comp. Biochem. Physiol. 82B, 1-15, 1985). 4. (1) The single-chain, single-domain globins are comparable in size to the vertebrate globins and exhibit the widest distribution. (A) Intracellular Hbs include: (i) the monomeric and polymeric Hbs of the polychaete Glycera; (ii) the tetrameric Hb of the echiuran Urechis; (iii) the dimeric Hbs of echinoderms such as Paracaudina and Caudina; and (iv) the dimeric and tetrameric Hbs of molluscs, the bivalves Scapharca, Anadara, Barbatia and Calyptogena. (B) Extracellular Hbs include: (i) the multiple monomeric and dimeric Hbs of the larva of the insect Chironomus; (ii) the Hbs of nematodes such as Trichostrongylus and Caenorhabditis; (iii) the globin chains forming tetramers and dodecamers and comprising approximately 2/3 of the giant (approximately 3600 kDa), hexagonal bilayer (HBL) Hbs of annelids, e.g. the oligochaete Lumbricus and the polychaete Tylorrhynchus and of the vestimentiferan Lamellibrachia; and (iv) the globin chains comprising the ca 400 kDa Hbs of Lamellibrachia and the pogonophoran Oligobrachia. (C) Cytoplasmic Hbs include: (i) the Mbs of molluscs, the gastropods Aplysia, Bursatella, Cerithedea, Nassa and Dolabella and the chiton Liolophura; (ii) the three Hb of the symbiont-harboring bivalve Lucina; (iii) the dimeric Hb of the bacterium Vitreoscilla; and (iv) plant Hbs, including the Hbs of symbiont-containing legumes (Lgbs), the Hbs of symbiont-containing non-leguminous plants and the Hbs in the roots of symbiont-free plants.(ABSTRACT TRUNCATED AT 400 WORDS)

Kinetics of ligand binding to Pseudoterranova decipiens and Ascaris suum hemoglobins and to Leu-29-->Tyr sperm whale myoglobin mutant

The kinetics of binding of O2, CO, and NO to the octameric, two-domain hemoglobins of the parasitic nematodes Pseudoterranova decipiens and Ascaris suum were determined on nanosecond and picosecond time scales using flash photolysis. The two nematode hemoglobins have very similar kinetic properties. On the picosecond time scale, they exhibit an unusual behavior in showing a geminate reaction with oxygen that is biphasic and dependent on the flash intensity. The geminate reaction with NO is also faster and more complete than for sperm whale myoglobin; however, in contrast to the O2 reaction, it is homogeneous. In addition, the oxygen dissociation rate of P. decipiens hemoglobin, 0.0035 s-1, is as low as that of A. suum hemoglobin, 0.004 s-1 (Gibson, Q. H., and Smith, M. H. (1965) Proc. R. Soc. Lond. B Biol. Sci. 163, 206-214). A mutant of sperm whale myoglobin suggested by sequence alignment of the nematode hemoglobins, Leu-29-->Tyr, did not have kinetic properties similar to them.

Induction of a proteoglycan core protein mRNA in mouse T lymphocytes

The mouse T lymphocyte cell line EL4.E1 synthesizes a proteoglycan core protein (PGCP) mRNA which is identical to serglycin mRNA found in mouse bone marrow-derived mast cells and a mouse mastocytoma cell line. PGCP mRNA was strongly induced in EL4.E1 cells by phorbol myristate acetate, which also induces mRNAs for several cytokines in these cells. In contrast to the induction of cytokine mRNAs, however, the induction of PGCP mRNA was not inhibited by Cyclosporine. PGCP mRNA was also inducible by allogeneic stimulation of normal mouse spleen cells, and by Con A stimulation of an Interleukin 2-producing T hybridoma cell line. A number of other cell lines expressed an identical or similar, mRNA, including two cytotoxic T cell lines, and three tumor cell lines related to bone marrow-derived cells. The levels of several proteoglycans have previously been reported to increase in cells of bone marrow origin under activating conditions, but this appears to be the first report of an induction of the corresponding PGCP mRNA by immune stimulation of T lymphocytes.

A commentary on: 'unexpected intron location in non-vertebrate globin genes', by: Moens et al. (FEBS letters, 312 (1992) 105-109)

We are submitting this commentary in order to prevent the confusion which Moens et al. may provoke in the minds of readers. Our comments are intended to point out the exclusion of some major issues and some errors which may mislead readers of this paper.

Characterization of beta 2-microglobulin transcripts from two teleost species

Using degenerate primers based on published beta 2-microglobulin sequences we were able to obtain an expected 111 base pairs (bp) polymerase chain reaction (PCR) fragment from tilapia genomic DNA. The sequence of this fragment showed a high degree of similarity to mouse beta 2-microglobulin at the protein level. We used these primers in an "anchored PCR" to obtain a 213 bp PCR fragment from a carp cDNA library. This was then used to clone a full-length beta 2-microglobulin cDNA from carp. The carp sequence showed the highest similarity to rabbit beta 2-microglobulin. Both sequences showed strong similarities to all previously published vertebrate beta 2-microglobulin sequences. The predicted protein secondary structure of both the carp and tilapia clones was almost identical to the corresponding regions of previously known vertebrate beta 2-microglobulin protein sequences. When either the carp or tilapia probes were used against corresponding northern blots, they hybridized to a message of approximately 800-1000 bases long, which corresponds to the previously published lengths of beta 2-microglobulin mRNAs. Southern blotting indicated that beta 2-microglobulin was encoded by a single copy gene in both cases. Phylogenetic analysis indicated that the sequences were related to the beta 2-microglobulins of higher vertebrates but grouped together in an ancestral position.

Assignment of human B2-1 gene (D17S811E) to chromosome 17qter by PCR analysis of somatic cell hybrids and fluorescence in situ hybridization

The human gene B2-1 has significant homology to the yeast gene SEC7. By PCR analysis of a human x rodent hybrid panel, the B2-1 gene was assigned to chromosome 17. Fluorescence in situ hybridization localized the gene to 17qter.

Immune function in free-ranging harbor seal (Phoca vitulina) mothers and their pups during lactation

Immune function in harbor seal mothers and their pups during lactation was studied on Sable Island, Nova Scotia, Canada, during the springs of 1989 and 1990. Methods included total white blood cell and differential counts, a Protein A enzyme linked immunosorbent assay (ELISA) for total immunoglobulin G (IgG) quantification, and functionality testing of lymphocytes in vitro using the T-cell mitogen concanavalin A (ConA). Lymphocyte functionality and total IgG levels were reduced in the mothers at the end of lactation, suggesting a reduction in immune function, possibly as a result of the stress of fasting, or hormonal changes associated with lactation and estrus. By contrast, lymphocyte functionality and total IgG levels in pups were low at birth and higher at the end of lactation. Pups at birth and females late in lactation may therefore be more susceptible to infection by viral and bacterial agents. This study represents the first broad examination of immune function in a free-ranging pinniped population.

Did the ancestral globin gene of plants and animals contain only two introns?

All vertebrate globin genes contain two introns, while plant globin genes contain three. It is widely thought that the plant gene structure reflects the structure of the primordial globin gene and that a common ancestor of all animals lost the central intron shortly after the divergence of plants and animals more than one billion years ago. The recent discovery of a discordant central intron in some animal globin genes suggests that this model is incorrect. We propose that the typical vertebrate two-intron gene structure is the primordial eukaryotic form, and that following the divergence of plants and animals, a common ancestor of plants gained a central intron in the globin gene.

Organization of non-vertebrate globin genes

The organization of non-vertebrate globin genes exhibits substantially more variability than the three-exon, two-intron structure of the vertebrate globin genes. (1) The structures of genes of the single-domain globin chains of the annelid Lumbricus and the mollusc Anadara, and the globin gene coding for the two-domain chains of the clam Barbatia, are similar to the vertebrate plan. (2) Genes for single-domain chains exist in bacteria and protozoa. Although the globin gene is highly expressed in the bacterium Vitreoscilla, the putative globin gene hmp in E. coli, which codes for a chimeric protein whose N-terminal moiety of 139 residues contains 67 residues identical to the Vitreoscilla globin, may be either unexpressed or expressed at very low levels, despite the presence of normal regulatory sequences. The DNA sequence of the globin gene of the protozoan Paramecium, determined recently by Yamauchi and collaborators, appears to consist of two exons separated by a short intron. (3) Among the lower eukaryotes, the yeasts Saccharomyces and Candida have chimeric proteins consisting of N-terminal globin and C-terminal flavoprotein moieties of about the same size. The structure of the gene for the chimeric protein of Saccharomyces exhibits no introns. According to Riggs, the presence of chimeric proteins in E. coli and other prokaryotes, such as Alcaligenes and Rhizobium, as well as in yeasts, suggests a previously unrecognized evolutionary pathway for hemoglobin, namely that of a multipurpose heme-binding domain attached to a variety of unrelated proteins with diverse functions. (4) The published globin gene sequences of the insect larva Chironomus have an intron-less structure and are present as clusters of multiple copies; the expression of the globin genes is tissue and developmental stage-specific. Furthermore, the expression of many of these genes has not yet been demonstrated despite the presence of apparently normal regulatory sequences in the two flanking regions. Unexpectedly, Bergtrom and collaborators have recently shown that at least three Ctt globin II beta genes contain putative introns. (5) Pohajdak and collaborators have found a seven-exon and six-intron structure for the globin gene of the nematode Pseudoterranova which codes for a two-domain globin chain. Although the second and fourth introns of the N-terminal domain correspond to the two introns found in vertebrate globin genes, the position of the third intron is close to that of the central intron in plant hemoglobins.(ABSTRACT TRUNCATED AT 400 WORDS)

Cloning and sequencing of a human cDNA from cytolytic NK/T cells with homology to yeast SEC7

Using the technique of subtractive hybridization (natural killer (NK) minus T helper cell line Jurkat), a human cDNA clone named B2-1 was isolated and sequenced. B2-1 transcripts are highly expressed in NK and peripheral T cells, but not in the T helper cell line used in the subtraction. Two overlapping cDNA clones contained 3309 bp, in agreement with a predicted size of 3.2 kb obtained by Northern blot analysis. The cDNA contained a 5' open reading frame encoding a 398 amino acid (aa) protein with a calculated M(r) of 46,383. The protein contains N-linked glycosylation sites and a site for phosphorylation by protein kinase C. Database homology searches show that the deduced protein is novel and has three discrete domains with significant homology to several structural proteins. The most striking homology was to yeast SEC7 in the central domain of the gene (57% identical over 466 bp) and also the protein level (42% identical amino acids; 39% conserved amino acids). SEC7 is a large protein (2008 amino acids) found on Golgi vesicles that plays a role in protein transport.

A nematode hemoglobin gene contains an intron previously thought to be unique to plants

Hemoglobin genes from plants and animals both have a characteristic chromosomal organization. Plant hemoglobin genes contains a unique intron inserted into the heme-binding domain of exon 2. This intron has not been previously reported in animal globin genes, and its loss was hypothesized to have occurred early in the evolution of hemoglobins. We report here a unique six-intron, seven-exon internally duplicated nematode hemoglobin gene that contains an intron equivalent to the plant central intron in its first repeat. This nematode hemoglobin gene has lost both the central and the normal third intron in its second repeat. The nematode globin also contains a unique intron between its secretory peptide leader sequence and its coding sequence, which is absent in other extracellular invertebrate globin genes. Possible models to explain the head-to-tail duplication of this gene are discussed.