Disclosed is an expression regulatory system for cell-specific transcription (expression) of a protein of interest, for example a cell cycle inducer that reactivates proliferation in adult or neonatal cardiomyocytes or insulin-producing beta cells. The expression regulatory system comprises a first nucleic acid that encodes a microRNA recognition element that specifically binds a target cell miR, and a translation suppressor protein； and a second nucleic acid that comprises a suppressor protein interaction motif that binds the translation suppressor protein, and a gene that encodes a protein of interest. When a cell of interest is co-transfected with the first and second nucleic acids of the system, the protein of interest expressed in a cell-specific fashion.
