Introduction of the RCAS retroviral gene transfer technology for functional genomic studies in the chicken The recently sequenced chicken genome now allows the identification of so far unknown genes. Some of them may play a potential role in the regulation of the immune system. In future studies roles of these genes have to be analyzed. At this in vitro studies will be used firstly. But in vivo functions of those genes will have to be described in the end. Therefore techniques for a fast and

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... icient over expression and knock down of candidate genes have to be established. Goal of this work was to prove the applicability of the RCAS retroviral vector system, which has been developed in the 1980s. This highly efficient system is based on a replication competent Rous Sarkoma-Virus and has already been used in cell and developmental biology studies in the chicken. However studies on its application after hatch haven´t been performed so far, despite its particular relevance for studies on the chicken immune system as it is widely immature at the time of hatch. In the first part of this work, a green fluorescent protein (GFP) expressing vector was constructed. An influence of the chicken line on the susceptibility of chicken embryo fibroblasts was detected in flow cytometric analyses. A possible reason could be the presence of endogenous retroviruses in less susceptible chicken lines leading to receptor interference. In accordance with this observation in in vivo tests retrovirus free chickens showed more homogenous plasma titers of RCAS based protein than a commercial chicken line. As GFP expression was predominantly seen in endothelial cells, the RCAS technology can be considered as particularly eligible for the expression of soluble proteins. Additionally viral protein was demonstrated to be expressed in bursal cells and heart muscle. For further characterization of the RCAS system vectors for the expression of the cytokine chBAFF or a soluble chBAFF receptor construct (huBCMA-Fc) were used. Plasma expression of b [...]