Development of Transgenic Chickens Expressing Human Parathormone Under the Control of a Ubiquitous Promoter by Using a Retrovirus Vector System

The science of genetically modified poultry

The exuberant development of targeted genome editing has revolutionized research on the chicken genome, generating chickens with beneficial parameters. The chicken model is a crucial experimental tool that can be utilized for drug manufacture, preclinical research, pathological observation, and other applications. In essence, tweaking the chicken’s genome has enabled the poultry industry to get more done with less, generating genetically modified chickens that lay eggs containing large amounts of lifesaving humanized drugs. The transition of gene editing from concept to practical application has been dramatically hastened by the development of programmable nucleases, bringing scientists closer than ever to the efficient producers of tomorrow’s medicines. Combining the developmental and physiological characteristics of the chicken with cutting-edge genome editing, the chicken furnishes a potent frontier that is foreseen to be actively pursued in the future. Herein we review the current and future prospects of gene editing in chickens and the contributions to the development of humanized pharmaceuticals.

Genetically engineered birds; pre-CRISPR and CRISPR era

Generating biopharmaceuticals in genetically engineered bioreactors continues to reign supreme. Hence, genetically engineered birds have attracted considerable attention from the biopharmaceutical industry. Fairly recent genome engineering methods have made genome manipulation an easy and affordable task. In this review, we first provide a broad overview of the approaches and main impediments ahead of generating efficient and reliable genetically engineered birds, and various factors that affect the fate of a transgene. This section provides an essential background for the rest of the review, in which we discuss and compare different genome manipulation methods in the pre-CRISPR and CRISPR era in the field of avian genome engineering.

Gene editing in birds takes flight

The application of gene editing (GE) technology to create precise changes to the genome of bird species will provide new and exciting opportunities for the biomedical, agricultural and biotechnology industries, as well as providing new approaches for producing research models. Recent advances in modifying both the somatic and germ cell lineages in chicken indicate that this species, and conceivably soon other avian species, has joined a growing number of model organisms in the gene editing revolution.

Study on the expression of human lysozyme in oviduct bioreactor mediated by recombinant avian adeno-associated virus

Due to its antimicrobial properties and low toxicity, human lysozyme (hLYZ) has broad application in the medical field and as a preservative used by the food industry. However, limited availability hinders its widespread use. Hence, we constructed a recombinant avian adeno-associated virus (rAAAV) that would specifically express hLYZ in the chicken oviduct and harvested hLYZ from the egg whites of laying hens. The oviduct-specific human lysozyme expression cassette flanked by avian adeno-associated virus (AAAV) inverted terminal repeats (ITRs) was subcloned into the modified baculovirus transfer vector pFBX, and then the recombinant baculovirus rBac-ITRLYZ was generated. The recombinant avian adeno-associated virus was produced by co-infecting Sf9 cells with rBac-ITRLYZ and the other 2 baculoviruses containing AAAV functional genes and structural genes, respectively. Electron microscopy and real-time PCR revealed that the recombinant viral particles were generated successfully with a typical AAAV morphology and a high titer. After one intravenous injection of each laying hen with 2 × 1011 viral particles, oviduct-specific expression of recombinant human lysozyme (rhLYZ) was detected by reverse transcription-PCR. The expression level of rhLYZ in the first wk increased to 258 ± 11.5 μg/mL, reached a maximum of 683 ± 16.4 μg/mL at the fifth wk, and then progressively declined during the succeeding 7 wk of the study. Western blotting indicated that the oviduct-expressed rhLYZ had the same molecular weight as the natural enzyme. These results indicate that an efficient and convenient oviduct bioreactor mediated by rAAAV has been established, and it is useful for production of other recombinant proteins.

Production of pigs expressing a transgene under the control of a tetracycline-inducible system

Pigs are anatomically and physiologically closer to humans than other laboratory animals. Transgenic (TG) pigs are widely used as models of human diseases. The aim of this study was to produce pigs expressing a tetracycline (Tet)-inducible transgene. The Tet-on system was first tested in infected donor cells. Porcine fetal fibroblasts were infected with a universal doxycycline-inducible vector containing the target gene enhanced green fluorescent protein (eGFP). At 1 day after treatment with 1 µg/ml doxycycline, the fluorescence intensity of these cells was increased. Somatic cell nuclear transfer (SCNT) was then performed using these donor cells. The Tet-on system was then tested in the generated porcine SCNT-TG embryos. Of 4,951 porcine SCNT-TG embryos generated, 850 were cultured in the presence of 1 µg/ml doxycycline in vitro. All of these embryos expressed eGFP and 15 embryos developed to blastocyst stage. The remaining 4,101 embryos were transferred to thirty three surrogate pigs from which thirty eight cloned TG piglets were obtained. PCR analysis showed that the transgene was inserted into the genome of each of these piglets. Two TG fibroblast cell lines were established from these TG piglets, and these cells were used as donor cells for re-cloning. The re-cloned SCNT embryos expressed the eGFP transgene under the control of doxycycline. These data show that the expression of transgenes in cloned TG pigs can be regulated by the Tet-on/off systems.

Molecular genetic studies of gene identification for osteoporosis

This review comprehensively summarizes the most important and representative molecular genetics studies of gene identification for osteoporosis published up to the end of September 2007. It is intended to constitute a sequential update of our previously published reviews covering the available data up to the end of 2004. Evidence from candidate gene-association studies, genome-wide linkage and association studies, as well as functional genomic studies (including gene-expression microarray and proteomics) on osteogenesis and osteoporosis, are reviewed separately. Studies of transgenic and knockout mice models relevant to osteoporosis are summarized. The major results of all studies are tabulated for comparison and ease of reference. Comments are made on the most notable findings and representative studies for their potential influence and implications on our present understanding of genetics of osteoporosis. The format adopted by this review should be ideal for accommodating future new advances and studies.