Establishing F1A-CreER(T2) Mice to Trace Fgf1 Expression in Adult Mouse Cardiomyocytes.

Fibroblast growth factor 1 (FGF1) regulates many biological and physiological processes. In mice, Fgf1 gene contains at least three upstream promoters and are alternatively spliced to the first protein coding exon, giving rise to different Fgf1 mRNA variants (1A, 1B and 1G). Among them, the Fgf1A transcript is predominantly expressed in the heart. FGF1 can induce cardiomyocyte regeneration and cardiogenesis in vitro and in vivo. Here, we generated a novel mouse line using the Fgf1A promoter (F1A) driving the expression of the inducible Cre recombinase (CreER(T2)). We firstly demonstrated that the highest mRNA expression of CreER(T2) were detected in the heart specifically of F1A-CreER(T2) mice, similar to that of Fgf1A mRNA. The F1A-CreER(T2) mice were crossed with ROSA26 mice, and the F1 mice were analyzed. The LacZ-positive signals were detected exclusively in the heart after tamoxifen administration. The CreER(T2)-mediated recombination in the tissues is monitored through LacZ-positive signals, indicating the in situ localization of F1A-positive cells. Consistently, these F1A-positive cells with RFP-positive signals or LacZ-positive blue signals were co-localized with cardiomyocytes expressing cardiac troponin T, suggesting cardiomyocyte-specific activation of Fgf1A promoter. Our data suggested that the F1A-CreER(T2) mouse line could be used for time-dependent and lineage tracing of Fgf1A-expressing cells in vivo.