DISEASE RESISTANCE AND OTHER APPLICATIONS OF TRANSGENESIS IN THE CHICKEN

Genetic modification of the chicken in terms of gene addition is now robust and efficient. Transgenes can be introduced by injection of lentiviral vectors into chick embryos or by transfection of transposon vectors into embryos or primordial germ cells in vitro. Lentiviral vectors are limited in the size of transgene they can incorporate but we have generated several different transgenic lines using HIV-derived vectors and have observed high levels of transgene expression and tissue-specific expression using regulatory sequences from several genes. M. McGrew (The Roslin Institute) has established primordial germ cell lines and effective methods for transfection with piggyBac and Tol2 transposon vectors. The primordial cells are injected into chick embryos where they populate the developing gonads and contribute to the germline in mature birds. The availability of primordial germ cell lines will also form the basis of using artificial site-specific nucleases for gene knockout and potentially gene targeting in the chicken. These technologies facilitate the application of transgenesis in the chicken for basic research and for potential applications in poultry breeding. The chick embryo is an invaluable model for studying vertebrate development as the embryos can be accessed in ovo or in culture at the earlier stages of development. Embryos can be transfected with transgenes by electroporation and manipulated to study many aspects of development. We are developing transgenic chickens in which fluorescent protein reporters are expressed either ubiquitously or in targeted cell types. These form the basis of novel tools for increasing the value of the chick embryo in studying development. We provide fertile eggs from these lines to other research groups and are investigating the development of macrophages using a macrophage-targeted reporter. The potential for the use of genetic modification to be used in poultry breeding can now be explored. Commercial poultry production is challenged by several major pathogens including avian influenza. Flocks can be protected by good biosecurity measures and/or vaccination but vaccination is not always effective. It may be possible to add novel genes to the chicken genome targeting avian influenza virus replication. We are developing this approach (with L. Tiley, Cambridge University) and have generated transgenic chickens that do not transmit avian influenza when directly infected with H5N1 virus.