Transgenic bioreactors

The Potential for Microalgae as Bioreactors to Produce Pharmaceuticals

As photosynthetic organisms, microalgae can efficiently convert solar energy into biomass. Microalgae are currently used as an important source of valuable natural biologically active molecules, such as carotenoids, chlorophyll, long-chain polyunsaturated fatty acids, phycobiliproteins, carotenoids and enzymes. Significant advances have been achieved in microalgae biotechnology over the last decade, and the use of microalgae as bioreactors for expressing recombinant proteins is receiving increased interest. Compared with the bioreactor systems that are currently in use, microalgae may be an attractive alternative for the production of pharmaceuticals, recombinant proteins and other valuable products. Products synthesized via the genetic engineering of microalgae include vaccines, antibodies, enzymes, blood-clotting factors, immune regulators, growth factors, hormones, and other valuable products, such as the anticancer agent Taxol. In this paper, we briefly compare the currently used bioreactor systems, summarize the progress in genetic engineering of microalgae, and discuss the potential for microalgae as bioreactors to produce pharmaceuticals.

Establishment of mammary gland model in vitro: culture and evaluation of a yak mammary epithelial cell line

This study aimed to establish yak mammary epithelial cells (YMECs) for an in vitro model of yak mammary gland biology. The primary culture of YMECs was obtained from mammary gland tissues of lactating yak and then characterized using immunocytochemistry, RT-PCR, and western blot analysis. Whether foreign genes could be transfected into the YMECs were examined by transfecting the EGFP gene into the cells. Finally, the effect of Staphylococcus aureus infection on YMECs was determined. The established YMECs retained the mammary epithelial cell characteristics. A spontaneously immortalized yak mammary epithelial cell line was established and could be continuously subcultured for more than 60 passages without senescence. The EGFP gene was successfully transferred into the YMECs, and the transfected cells could be maintained for a long duration in the culture by continuous subculturing. The cells expressed more antimicrobial peptides upon S.aureus invasion. Therefore, the established cell line could be considered a model system to understand yak mammary gland biology.

Cloning and characterization of 5' upstream promoter region of rat WAP gene

Regulatory regions of genes encoding milk proteins are frequently used to produce in the mammary gland of transgenic animals a variety of pharmaceutically and medically important human proteins. One such example is the whey acidic protein (WAP) promoter region, identified so far in the genome of mouse, rat, rabbit, camel, pig, brushtail possum and Tammar wallaby. The aim of the present study was cloning and characterization of the 5' upstream promoter region of rat WAP gene. Using Genome Walking procedure, we cloned the region extending from -849 to -3671 bp. We have shown that there are two conserved regions highly similar to hypersensitive sites present in mouse and rabbit upstream region of WAP gene with binding sites for STAT5 transcription factor, essential for expression of WAP gene in mammary glands during lactation. We characterized dispersed and tandem repeats in the upstream region of rat WAP gen localized not far away from the translation initiation site.

Synthesis and chromatographic purification of recombinant human pituitary hormones

Recombinant DNA-derived proteins and, in particular, human pituitary hormones, are increasingly used for research, diagnostic and therapeutic purposes. This trend has demanded new synthetic approaches and improved purification techniques. The type and sequence of the purification steps have to be selected in accordance with the cloning and protein expression strategy, the host organism and cellular localization of the protein of interest, with a view to producing the desired product at a required purity, biological activity and acceptable cost. This review article describes and analyzes the main synthetic and purification strategies that have been used for the production of recombinant human growth hormone, prolactin, thyrotropin, luteinizing hormone and follicle-stimulating hormone, giving special consideration to the few published downstream processes utilized by the biotechnology industry. Practically all types of prokaryotic and eukaryotic organisms utilized for this purpose are also reviewed.

Renal tubule-specific expression and urinary secretion of human growth hormone: a kidney-based transgenic bioreactor growth

Tissue-specific expression of human genes and secretion of human proteins into the body fluids in transgenic animals provides an important means of manufacturing large-quantity and high-quality pharmaceuticals. The present study demonstrates using transgenic mice that a 3.0 kb promoter of the mouse Tamm-Horsfall protein (THP, or uromodulin) gene directs the specific expression of human growth hormone (hGH) gene in the kidney followed by the secretion of hGH protein into the urine. hGH expression was detected in renal tubules that actively produce the THP, that is, the ascending limb of Henle's loop and distal convoluted tubules. Up to 500 ng/ml of hGH was detected in the urine, and this level remained constant throughout the 10-month observation period. hGH was also detectable in the stomach epithelium and serum in two of the transgenic lines, suggesting position-dependent effects of the transgene and leakage of hGH from the site of synthesis into the bloodstream, respectively. These results indicate that the 3.0 kb mouse THP promoter is primarily kidney-specific and can be used to convert kidney into a bioreactor in transgenic animals to produce recombinant proteins. Given the capacity of urine production independent of age, sex and lactation, the ease of urinary protein purification, and the potentially distinct machinery for post-translational modifications in the kidney epithelial cells, the kidney-based transgenic bioreactor may offer unique opportunities for producing certain complex pharmaceuticals.

Production of transgenic miniature pigs by pronuclear microinjection

Miniature pig is an attractive animal for a wide range of research fields, such as medicine and pharmacology, because of its small size, the possibility of breeding it under minimum environmental controls and the physiology that is potentially similar to that of human. Although transgenic technology is useful for the analysis of gene function and for the development of model animals for various diseases, there have not yet been any reports on producing transgenic miniature pig. This study is the first successful report concerning the production of transgenic miniature pig by pronuclear microinjection. The huntingtin gene cloned from miniature pig, which is a homologue of candidate gene for Huntington's disease, connected with rat neuron-specific enolase promoter region, was injected into a pronucleus of fertilized eggs with micromanipulator. The eggs were transferred into the oviduct of recipient miniature pigs, whose estrus cycles were previously synchronized with a progesterone analogue. A total of 402 injected eggs from 171 donors were transferred to 23 synchronized recipients. Sixteen of them maintained pregnancy and delivered 65 young, and one resulted in abortion. Five of the 68 offspring (three of which were aborted) were determined to have transgene by PCR and Southern analysis. The overall rate of transgenic production was 1.24% (transgenic/injected eggs). This study provides the first success and useful information regarding production of transgenic miniature pig for biomedical research.

Transgenic farm animals: applications in agriculture and biomedicine

During the last decade, tremendous progress has been made in the area of transgenic farm animals. While there are many important transgenic farm animal applications in agriculture, funding has been very limited and progress has been rather slow in this area. Encouragingly, the potential applications of transgenic farm animals as bioreactors for producing human therapeutic proteins and as organ donors for transplantations in humans have attracted vast funding from the private sectors. Several transgenic animal products are already in various phases of clinical trials. Estimates are, that in the near future, the worlds demands on human pharmaceutical proteins may largely be met by transgenic farm animals. While there are still major challenges ahead in the area of xenotransplantation using transgenic animal organs, transgenic tissues or cells have demonstrated promising results as a potential tool for gene therapy. Recent development on cloning, embryonic stem cells and alternative transgenic methods may further expand the transgenic applications in both agriculture and biomedicine.

A new biological strategy for high productivity of recombinant proteins in animal cells by the use of hypoxia-response enhancer

Oxygen supply is one of the major problems in the production of useful proteins by cultured animal cells and therefore it is of importance to devise a system by which a high productivity of human therapeutic recombinant proteins can be maintained or enhanced under low oxygen concentrations. A number of hypoxia-inducible genes have been found in animal cells and the induction in most cases is due to hypoxic activation of the gene transcription. A consensus sequence (HRE = hypoxia-response enhancer) responsible for the hypoxic activation exists in these genes and the binding of a protein, which is widely distributed in animal cells, to this sequence responding to hypoxia activates the promoter activity. The promoter of lactate dehydrogenase A gene is active in Chinese hamster ovary (CHO) cells and the vicinal HRE stimulates the promoter activity efficiently in hypoxia. We have prepared a number of permanent CHO cell lines producing recombinant human erythropoietin (Epo) under control of this promoter/HRE. Epo production was highly hypoxia-inducible when the wild-type of HRE was used but uninducible when the mutant HRE was used. There was little difference in the in vitro and in vivo activities, and glycosylation between Epo produced by the cells cultured in 21% and 2% oxygen. Furthermore, forced expression of hypoxia-inducible factor-1alpha (HIF-1alpha) enhanced Epo production in all oxygen concentrations. These results indicate that a biological strategy based on the hypoxic induction of gene transcription provides a novel system which guarantees a high productivity even uner low oxygen concentrations.

Seminal vesicle production and secretion of growth hormone into seminal fluid

Production of foreign proteins in the tissues of transgenic animals represents an efficient and economical method of producing therapeutic and pharmaceutical proteins. In this study, we demonstrate that the mouse P12 gene promoter specific to the male accessory sex gland can be used to generate transgenic mice that express human growth hormone (hGH) in their seminal vesicle epithelium. The hGH is secreted into the ejaculated seminal fluids with the seminal vesicle lumen contents containing concentrations of up to 0.5 mg/ml. As semen is a body fluid that can be collected easily on a continuous basis, the production of transgenic animals expressing pharmaceutical proteins into their seminal fluid could prove to be a viable alternative to use of the mammary gland as a bioreactor.

Transgenic bioreactors

Since the generation of the first transgenic mice in 1980, transgene technology has also been successfully applied to large farm animals. Although this technology can be employed to improve certain production traits of livestock, this approach has not been very successful so far owing to unwanted effects encountered in the production animals. However, by using tissue-specific targeting of the transgene expression, it is possible to produce heterologous proteins in the extracellular space of large transgenic farm animals. Even though some recombinant proteins, such as human hemoglobin, have been produced in the blood of transgenic pigs, in the majority of the cases mammary gland targeted expression of the transgene has been employed. Using production genes driven by regulatory sequences of milk protein genes a number of valuable therapeutic proteins have been produced in the milk of transgenic bioreactors, ranging from rabbits to dairy cattle. Unlike bacterial fermentors, the mammary gland of transgenic bioreactors appear to carry out proper postsynthetic modifications of human proteins required for full biological activity. In comparison with mammalian cell bioreactors, transgenic livestock with mammary gland targeted expression seems to be able to produce valuable human therapeutic proteins at very low cost. Although not one transgenically produced therapeutic protein is yet on the market, the first such proteins have recently entered or even completed clinical trials required for their approval.

High efficiency DNA delivery into swine oocytes and embryos by electronic pulse delivery (EPD)

The production of transgenic swine for xenotransplantation has been proposed as an optimal option to overcome the chronic shortage of human organ donors. Generation of genetically engineered swine has been elusive due to the difficulties in gene transfer. In order to achieve effective gene delivery, a key step for the genetic modification, we applied electronic pulse delivery (EPD) technology to introduce H2Kb-DC DNA construct into swine eggs. Using the developed EPD Protocols, we have achieved good viability of the EPD treated oocytes, satisfactory embryonic development of the EPD treated embryos, and stable DNA transfer into the swine embryos with high efficiency. Thus, application of the EPD technology promises to effectively facilitate the generation of large transgenic mammals.

An in vitro approach to ruminant mammary gland biology

This review discusses both fundamental and applied in vitro studies on ruminant mammary gland biology and summarizes progress made over the last decade in development of in vitro techniques to study growth, function and pathology of the mammary gland. The advantages and limitations of different in vitro systems are considered including explant cultures, primary cell cultures and immortalized lines of mammary-derived cells from cow, sheep and goat. The cell growth, differentiation and response to lactogenic hormones and growth factors are discussed as well as the relevance of the cell behavior in different culture conditions.

Co-integration of beta-lactoglobulin/human serum albumin hybrid genes with the entire beta-lactoglobulin gene or the matrix attachment region element: repression of human serum albumin and beta-lactoglobulin expression in the mammary gland and dual regulation of the transgenes

The effect of co-integration of the entire beta-lactoglobulin (BLG) gene or matrix attachment region (MAR) sequences on the expression of various BLG/ human serum albumin (HSA) gene constructs was tested in transgenic mice. These former sequences were chosen because of their reported ability to insulate transgenes from the neighboring host genomic DNA sequences and/or to provide a more permissive transcriptional environment. When introduced alone, a cDNA-based BLG/HSA construct was expressed in 60% of transgenic strains and HSA was secreted at levels up to 0.3 mg/ml into the milk. Upon co-integration with either the entire BLG gene or MAR element, HSA RNA and protein expression were completely abrogated. While the co-integrated BLG gene suppressed the proportion of expresser strains carrying cDNA as well as genomic BLG/HSA constructs, the MAR element only exerted its negative effect on the cDNA-based BLG/HSA construct. In transgenics expressing both HSA and BLG, the tissue specificity and developmental patterns of BLG expression were altered and resembled the less stringent pattern of the BLG/HSA expression. These results demonstrate that rescue of transgene expression through co-integration with BLG or MAR sequences do not apply universally.

Recombinant protein production in transgenic animals

The engineering of animals for recombinant protein production has gone beyond the stage of identifying proper regulatory sequences. Efforts are now spent on the generation of transgenic animals that process heterologous proteins more efficiently. Another line of research is the development of strategies aimed at bypassing pronuclear microinjection.

Detection of microinjected genes in bovine preimplantation embryos with combined DNA digestion and polymerase chain reaction

We have developed a simple digestion-polymerase chain reaction (PCR) assay for a simultaneous transgene detection and sexing of pronucleus-injected bovine preimplantation embryos. Bovine embryos were microinjected with dam-methylated gene construct and cultured in vitro for 6-7 days after the injections. The developed blastocysts and compact morulae were bisected and the embryonic biopsies representing mainly trophoblasts were subjected to the digestion-PCR, while the biopsied embryos remained in culture. Embryonic DNA was released with proteinase K and the samples were digested with a Dpnl-Bal31 mixture before the PCR amplification of the transgene, bovine alpha S1-casein, and bovine Y-chromosome fragments in the same reaction. The whole assay from biopsy to electrophoresis took less than 6 hr. The digestion removed up to 50 fg of dam-methylated transgene copies (unintegrated or contaminants) and also a few hundred copies of contaminating PCR products from the embryonic samples. The digestion-PCR assay eliminated all transgene contaminations from noninjected blastocysts, which were exposed to the microinjection DNA during the stay in injection chambers, and reduced the amount of transgene-positive embryos among pronucleus-injected blastocysts as compared with unmodified PCR. Analysis of 486 microinjected bovine embryo biopsies in 13 separate experiments revealed that we were able to sex 398 (82%) of the biopsies and 77 (19%) of the biopsies were scored as transgene positive and 57 (14%) as transgene questionable. Upon reanalysis of 41 of the biopsied embryos, 38 (93%) of the embryos were observed to be transgene negative and 2 questionable in both assays and uneven distribution of transgene copies was observed in one embryo. The results from sexing were in accordance with biopsies and remaining embryos in 38 (93%) of the embryos.

Transgenic models for eye malformations

Several lines of transgenic mice developing eye malformations have been described in the literature and appear to be of increasing interest for the study of eye teratology in humans, since gene expression and regulation can be studied in the developing animal. Transgenic applications are briefly described here and an overview of existing transgenic mouse models carrying different eye abnormalities is given according to the major diagnosis (e.g., cataract, microphthalmia, anterior segment dysgenesis, retinal dysplasia). Interestingly, many transgenic models exhibit pathological findings similar to those observed in human pediatric ophthalmology. Unfortunately, detailed embryological studies in transgenic mice bearing congenital eye malformations are not available for all lines. Thus, the importance of creating further transgenic models to study the function of morphogenes and growth factors in eye development is also discussed.