A narrow developmental window defines PKN2's essential role in ventricular chamber morphogenesis

Protein kinase N2 (PKN2) is essential for embryonic heart development, but the precise timing and cellular requirement in cardiomyocytes are not well understood. Here we show that, in a constitutive cardiomyocyte-specific knockout (cKO) of PKN2, we observe partially penetrant early postnatal lethality, non-progressive systolic dysfunction in survivors, and a distinctive "coin-pouch" ventricular geometry resembling the embryonic shape, linking the phenotype to a developmental origin rather than ongoing pathology. By tracking heart morphogenesis, we find that mutant and control hearts are still grossly indistinguishable at E10.5, defining a stage prior to overt morphological divergence. Integrative RNA-seq, proteomics, and phosphoproteomics at E10.5 reveal transcriptional and proteomic signatures consistent with induction of actin cytoskeleton and motility-associated programs alongside repression of chromosome-condensation and mitotic modules in PKN2 cKO hearts. These molecular changes coincide with reduced cardiomyocyte proliferation at E10.5-E11.5 and early divergence in ventricular-shape trajectories. Quantitative light-sheet microscopy-based morphometrics of inducible cardiomyocyte-specific PKN2 knockout hearts pinpoints the critical dependence window: tamoxifen administration at E7.5 reproduces the ventricular geometry characteristic of constitutive PKN2 cKO hearts, whereas administration at E10.5 spares gross morphology. Together, these data show that cardiomyocytes depend on PKN2 during an early proliferative phase, characterized by cytoskeletal remodeling and motility-associated programs, that contributes to ventricular wall formation, after which PKN2 becomes dispensable for gross ventricular chamber morphogenesis. This temporally restricted requirement reconciles previous observations of PKN2's essential role in mesodermal and epithelial morphogenesis, suggesting a shared function in coordinating cytoskeletal remodeling with tissue expansion during organogenesis.