Irx4 identifies a chamber‐specific cell population that contributes to ventricular myocardium development

COVER PHOTOGRAPH: A merged confocal image of a primary cardiomyocyte culture, derived from the ventricles of a postnatal day‐3 mouse heart. Cardiomyocytes were co‐stained with primary antibodies to IRX4, a ventricle‐specific transcription factor, and the cardiomyocyte‐specific marker, cardiac troponin T. A goat anti‐mouse IgM Alexa 568 secondary (red) was used to detect IRX4 primary antibody, and goat anti‐mouse IgG Alexa 488 secondary (green) was used to report localization of the cardiac troponin T primary antibody. Nuclei were labeled with Hoechst dye. This result shows that IRX4 is restricted to the cytoplasm of postnatal day 3 ventricular myocytes. At postnatal day 5, IRX4 is localized to the nuclei of cardiomyocytes. From Nelson et al., Developmental Dynamics 243:381–392.