Fig. 1. (A) Structure of the 5' regulatory region of mouse Nfatc1, which contains two independent promoters, P1 and P2, for transcription of Nfatc1. and Nfatc1.ß isoforms, respectively. (B) RT-PCR analysis using exon (isoform)-specific primers showing that the Nfatc1. isoform is abundant in the cultured primary E11.5 endocardial cells (ECC) and its transcripts is detected by a 35-cycle amplification, whereas the Nfatc1.ß isoform is detected only after a 40-cycle amplification. The structures of the isoforms are shown on the left.