show Abstracthide AbstractIn this study we perform the transcriptomic analysis of embryonic tissues involved in thymus formation. Using the chick-quail model, we first mapped the pharyngeal endoderm regions with thymus formation potential, the 3rd and 4th PP pharyngeal pouch (3/4PP) and 2PP. The transcriptomes of 2PP and 3/4PP endoderm were obtain from isolated tissues of quail embryos with 3 days of development.