Inheritance and tissue-specific expression of transgenes in rabbits and pigs

Evaluation of two methods to isolate Schwann cells from murine sciatic nerve

BACKGROUND

Schwann cells (SC) and macrophages play key roles in the response to peripheral nerve injury (PNI). Accurate isolation of such cells is essential for further analyses that can lead to better understanding of the repair process after PNI. Separation of live SC from the injury site without culture enrichment is necessary for targeted gene expression analysis.

NEW METHODS

Two flow cytometric techniques are presented for rapid enrichment of live SC and macrophages from injured murine peripheral nerve without the need for culture.

RESULTS

SC were isolated by fluorescent activated cell sorting (FACS) using transgenic expression of eGFP in SC, or by exclusion of other cell types collected from the injury site.

COMPARISON WITH EXISTING METHOD(S)

Gene expression analyses of peripheral nerve repair have commonly used whole nerve lysates. Isolating SC allows more accurate understanding of their specific role in repair. SC are commonly enriched from nerve by culture, however this changes gene expression patterns and limits the utility for transcriptomic analysis. The surface marker p75-NTR has variable expression in different SC phenotypes and during the course of injury and repair. Using p75-NTR for SC isolation might enrich only a subset of SC. More stably expressed lineage markers for SC are intracellular and not suitable for sorting for gene expression. The methods used here avoid the requirement for surface marker labeling of SC.

CONCLUSION

Gene expression analysis of sorted cells from both methods showed successful enrichment of SC. Lineage markers such as Map1b, p75-NTR and S100b were enriched in the sorted SC population. SC sorting by eGFP expression showed improved enrichment, particularly of mature myelinating genes, although this could represent sampling of a subset of SC.

Precision editing of large animal genomes

Transgenic animals are an important source of protein and nutrition for most humans and will play key roles in satisfying the increasing demand for food in an ever-increasing world population. The past decade has experienced a revolution in the development of methods that permit the introduction of specific alterations to complex genomes. This precision will enhance genome-based improvement of farm animals for food production. Precision genetics also will enhance the development of therapeutic biomaterials and models of human disease as resources for the development of advanced patient therapies.

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.

Transgenic rabbits for the production of biologically-active recombinant proteins in the milk

The use of live bioreactors for the expression of human genes in the mammary gland of transgenic animals is one of the most cost-effective ways for the production of valuable recombinant therapeutic proteins. Among the transgenic species used so far, rabbits are good candidates for the expression of tens to hundreds of grams of complex proteins in the milk during lactation. The lactating mammary gland of rabbits has proven to be effective in the processing of complex proteins. In this work. the potential use of rabbits as bioreactors is discussed based on our results and the published data.

Transgenic animal bioreactors in biotechnology and production of blood proteins

The regulatory elements of genes used to target the tissue-specific expression of heterologous human proteins have been studied in vitro and in transgenic mice. Hybrid genes exhibiting the desired performance have been introduced into large animals. Complex proteins like protein C, factor IX, factor VIII, fibrinogen and hemoglobin, in addition to simpler proteins like alpha 1-antitrypsin, antithrombin III, albumin and tissue plasminogen activator have been produced in transgenic livestock. The amount of functional protein secreted when the transgene is expressed at high levels may be limited by the required posttranslational modifications in host tissues. This can be overcome by engineering the transgenic bioreactor to express the appropriate modifying enzymes. Genetically engineered livestock are thus rapidly becoming a choice for the production of recombinant human blood proteins.

High-level expression of bovine alpha s1-casein in milk of transgenic mice

The bovine alpha s1-casein gene, isolated from a cosmid library, was introduced into the murine germline. Transgene expression occurred in all transgenic mice, and was confined to the lactating mammary gland. Half of the mouse lines (five out of ten) expressed at relatively high expression levels (> 1 mg ml-1). The highest levels of expression were obtained with a transgene containing 14.2 kb of 5' flanking sequence, in two cases expression levels comparable to (10 mg ml-1) or well above (20 mg ml-1) alpha s1-casein levels in bovine milk were obtained. Transcription initiation occurred at the same site in the bovine alpha s1-casein gene in transgenic mouse as in the cow. A marked induction of expression occurred at parturition rather than at mid-pregnancy, and thus resembled the bovine rather than the murine developmental expression pattern. Bovine alpha s1-casein specific immunoblotting and RIA were developed for characterization and quantification of the recombinant protein. Using these assays, the properties of the recombinant protein could not be distinguished from those of the natural bovine protein. In spite of the high-level tissue-specific and correctly regulated developmental expression of the transgene, expression levels were integration-site dependent. This may indicate that not all cis-acting regulatory elements involved in bovine alpha s1-casein expression were included in the transgene.