Development of oviduct specific promoter system for transgenic chicken bioreactors

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To establish a transgenic bioreactor system using chickens for production of recombinant proteins into their eggs, a specific-expression system of target protein was developed. Although it is necessary to construct an oviduct-specific expression system, whole control region of an oviduct-specific promoter such as ovalbumin promoter cannot be introduced into a retroviral vector for gene delivery, since retroviral vectors have size limitation of an insert gene. Thus, a synthetic promoter system, in which a minimum control region for the tissue-specific expression and an artificial induction system for high-level expression were combined, was designed. First of all, tissue-specific control regions of ovalbumin promoter were divided into DNase hyper-sensitive regions according to a previous study, and an effective region for oviduct-specific expression was determined. During this study, it was found that a transcription factor, YY1 binds to a negative-control region of ovalbumin promoter. The synthetic promoter system, firstly designed in this study, including a positive feed-back of expression of the transactivator could induce a target protein with high level. However, leak expression had occurred and modification of the synthetic promoter system was required. By replacing the minimum promoter included in the synthetic promoter with a small region of ovalbumin promoter including TATA box and proximal region, leak expression could be minimized. These results indicate that the synthetic promoter construct for oviduct-specific and high-level expression can be used for transgenic chicken bioreactors..