Diminished cardiac performance after Prdm16 inactivation. (A) Survival of male and female Prdm16^csp1/wt mice is normal until the age of 8 month (n > 13 each group). (B) Eight-month-old Prdm16^csp1/wt mice of both sexes have a reduced absolute body weight. Normalization against tibia length demonstrated a diminished relative heart and LV weight in Prdm16^csp1/wt mutants (n > 13 each group). (C) M-mode images illustrate the heart phenotype in Prdm16^csp1/wt mice as assessed with echocardiography. (D) At the age of 8 months, Prdm16^csp1/wt mice of both sexes have diminished cardiac function as illustrated by stroke volume, cardiac output, and ejection fraction (EF) (n > 12 each group). Full echocardiography data are available in Supplementary material online, Tables SIV–SVI in the Data Supplement. (E) Plasma brain natriuretic peptide (Bnp) levels were determined with ELISA (n > 5 each group). (F) Histological analysis with H&E staining reveals normal tissue organization in female Prdm16^csp1/wt hearts. Scale bars in E and F are 500 µm (full heart) and 50 µm (inset). (G) Histological staining for fibrosis with Picro-Sirius red is negative in female Prdm16^csp1/wt heart tissue. (H) The cell area of female heart muscle (cross sections) stained with wheat germ agglutinin (WGA) is significantly reduced (n = 5, each n includes >300 cells). Nuclei were stained with DAPI. Scale bar is 20 µm. Statistical analysis was performed with unpaired t-test (P < 0.05).