Fig 1. The Hand1^LV-Cre transgenic allele recombines within the embryonic LV.

A) Schematic of the mouse Hand1^LV-Cre transgene, in which a 744bp Hand1 LV-specific enhancer and ~2.7Kb Hand1 endogenous promoter regulate an eGFPCre expression cassette. B-M) X-gal staining to detect the R26R^lacZ reporter allele demonstrates that, like the Hand1^eGFPCre knock-in allele (B, D, F, H, J, L), Hand1^LV-Cre activity initiates in the LV (white arrows) between E8.5 and E9.5 (C, E). Cre-lineage cells are detectable within the LV at E10.5 (G, I) and E15.5 (K, M), but not within the epicardium (H, I; black arrowheads) or the outflow tract (H, I; black arrows). la–left atrium, ra–right atrium, lv–left ventricle, rv–right ventricle.