A compact minimal promoter-feedback circuit enables enhanced oviduct-restricted transgene expression in chickens

Precise spatial restriction of transgene expression is essential for safe in vivo production of bioactive proteins; however, regulatory elements that confer tissue specificity often span large genomic regions and are incompatible with size-limited viral vectors. Here, we report a compact synthetic promoter-feedback circuit that enables enhanced, oviduct-restricted transgene expression in chickens. By combining a minimal ovalbumin promoter (<200 bp) with a tetracycline-responsive element (TRE)-tTA positive feedback loop, we established a viral vector-compatible expression module that achieves enhanced transcriptional output while preserving tissue specificity. This system was validated in vitro and in genetically modified chickens. As a functional demonstration, chickens expressing transforming growth factor beta 1 (TGF-β1) specifically in egg white were generated. TGF-β1 accumulated predominantly as a presumptive latent/pro-form consisting of the latency-associated peptide (LAP)/pro-domain and the mature TGF-β1 dimer, at a semi-quantitatively estimated level of approximately 110 µg/mL, and remained detectable for over 2 years. Oral administration of TGF-β1-containing egg white significantly attenuated inflammation in a murine DSS-induced colitis model. Together, these findings establish a modular, size-efficient transcriptional enhancement platform that enables robust tissue-restricted expression in vivo. This strategy provides a generalizable framework for overcoming regulatory size constraints in viral vector-mediated gene delivery and expands the potential for producing edible biopharmaceuticals in transgenic livestock.