A new Prdm1-Cre line is suitable for studying the second heart field development.

The second heart field (SHF) plays a pivotal role in heart development, particularly in outflow tract (OFT) morphogenesis and septation, as well as in the expansion of the right ventricle (RV). Two mouse Cre lines, the Mef2c-AHF-Cre (Mef2c-Cre) and Isl1-Cre, have been widely used to study the SHF development. However, Cre activity is triggered not only in the SHF but also in the RV in the Mef2c-Cre mice, and in the Isl1-Cre mice, Cre activation is not SHF-specific. Therefore, a more suitable SHF-Cre line is desirable for better understanding SHF development. Here, we generated and characterized the Prdm1-Cre knock-in mice. In comparison with Mef2c-Cre mice, the Cre activity is similar in the pharyngeal and splanchnic mesoderm, and in the OFT of the Prdm1-Cre mice. Nonetheless, it was noticed that Cre expression is largely reduced in the RV of Prdm1-Cre mice compared to the Mef2c-Cre mice. Furthermore, we deleted Hand2, Nkx2-5, Pdk1 and Tbx20 using both Mef2c-Cre and Prdm1-Cre mice to study OFT morphogenesis and septation, making a comparison between these two Cre lines. New insights were obtained in understanding SHF development including differentiation into cardiomyocytes in the OFT using Prdm1-Cre mice. In conclusion, we found that Prdm1-Cre mouse line is a more appropriate tool to monitor SHF development, while the Mef2c-Cre mice are excellent in studying the role and function of the SHF in OFT morphogenesis and septation.