Generation of rat lungs by blastocyst complementation in Fgfr2b-deficient mouse model

Regenerative medicine is a tool to compensate for the shortage of lungs for transplantation, but it remains difficult to construct a lung in vitro due to the complex three-dimensional structures and multiple cell types required. A blastocyst complementation method using interspecies chimeric animals has been attracting attention as a way to create complex organs in animals, but successful lung formation has not yet been achieved. Here, we applied a "reverse-blastocyst complementation method" to clarify the conditions required to form lungs in an Fgfr2b-deficient mouse model. We then successfully formed a rat-derived lung in the mouse model without generating a mouse line by applying a tetraploid-based organ-complementation method. Importantly, rat lung epithelial cells retained their developmental timing even in the mouse body. This result provides useful insights regarding the need to overcome the barrier of species-specific developmental timing in order to generate functional lungs in interspecies chimeras.