a, Echocardiographic assessment of LVEF in Meis1-iKO hearts at the indicated time points post-MI. b, Immunostaining of Meis1-interacting Hox proteins (red), cardiac troponin T (green), and nucleus (blue) at P1, P7 and 7 days after P1 MI. c, Western blot analysis of Meis1 and Hox proteins during regenerative stages. GAPDH serves as loading control. d, Coimmunoprecipitation of Meis1 from total heart extracts at P1 and P7. e, Coimmunoprecipitation from Fig. 1c, with negative controls (IgG and DKO heart). f, Coimmunoprecipitation from Fig. 1d, with negative controls (IgG and DKO heart). g, PLA of Meis1 and Hoxb13 in P7 DKO heart; serves as negative control for PLA assay in Fig. 1e. h, Schematic of targeting strategy for generation of cardiomyocyte-specific Hoxb13 mutants. Partial map of the Hoxb13 floxed allele (top), and of the knockout allele (bottom) following cardiomyocyte-specific Cre-mediated excision. Exons and loxP sites are indicated as rectangles and triangles, respectively. i, PCR analysis of heart DNA obtained by crossing Hoxb13loxP/loxP (female) mutants with MHC-cre (male) transgenic mice. Left lane shows Hoxb13loxP/loxP. Middle lane indicates cardiomyocyte-specific Cre. Right lane indicates that the deleted allele is present in cardiomyocyte DNA of this offspring. j, Top, western blot of protein extracts from hearts of constitutive (left) or inducible (right) Hoxb13 knockout and Hoxb13fl/fl littermate mice. GAPDH serves as loading control. Bottom, densitometry quantification of the above western blot. k, Control and Hoxb13-KO P14 hearts stained for Meis1 (red), cardiac troponin T (green), and nucleus (blue). Arrowheads indicated Meis1-expressing cardiomyocytes, and arrows indicate Meis1-expressing non-cardiomyocytes. l, Representative echocardiography, ejection fraction and fraction shortening in Hoxb13-KO mice P14 hearts. m, Representative images of Masson’s trichrome staining of control and Hoxb13-iKO hearts at 14 days post-deletion. n, Representative images of immunostaining for TUNEL (green), cardiac troponin T (red) and nucleus (blue) (left) and quantification (right) 14 days post-deletion. Arrow indicates TUNEL-positive cardiomyocytes. Data are mean ± s.e.m.; unpaired two-sided t-test. Data in b–f, g, i, k, m were independently repeated three times with similar results. *P < 0.05, **P < 0.01. For gel source data, see Supplementary Fig. 1. For n values, see Methods. Scale bars, 10 μm (b, k, n), 50 μm (g), 1 mm (m). Source Data