TBX5 and infection: For iCM reprogramming, we infected transgenic αMHC-GFP MEFs with a cocktail of monocistronic Gata4, Mef2c, and Tbx5 (GMT) retroviruses and found that GFP could be first observed from day 2 post-infection (DPI-2), which was consistent with the observation that a high-level overexpression of GMT was achieved around 48 h post-infection (Figure S1A).