Left ventricular noncompaction cardiomyopathy (LVNC; OMIM No. 604169) is anatomically characterized by excess trabeculation and deep intertrabecular recesses. It is the third most prevalent pediatric Show more
Left ventricular noncompaction cardiomyopathy (LVNC; OMIM No. 604169) is anatomically characterized by excess trabeculation and deep intertrabecular recesses. It is the third most prevalent pediatric cardiomyopathy. Despite its clinical significance, the pathogenesis of LVNC remains uncertain. We examined Numb expression in epicardial cells (EpiCs) and epicardial-derived cells (EPDCs) using a mCherry::Numb knock-in mouse line; used Numb is enriched in EpiCs and EPDCs. In EDKO hearts, EPDCs displayed abnormal differentiation, and their migration was arrested at the outer compact zone, resulting in the absence of EPDCs in the inner compact zone and trabeculae. The EDKO hearts displayed LVNC, and inducible EpiC-specific Ablation of NFPs (Numb family proteins) in EpiCs disrupted the invasion and differentiation of EPDCs and the communication between cardiomyocytes and other cells, and caused LVNC. The epithelial-mesenchymal transition and compaction defects can be partially rescued by exogenous Fgf2 supplementation. Our findings highlight an essential role for the epicardial NFPs-Fgf/Fgfr axis in regulating ventricular compaction. Show less
Epithelial apico-basal polarity is established through the asymmetric cortical distribution of the Par, Crumbs and Scribble polarity modules. Apical (Par and Crumbs) and basolateral (Scribble) polarit Show more
Epithelial apico-basal polarity is established through the asymmetric cortical distribution of the Par, Crumbs and Scribble polarity modules. Apical (Par and Crumbs) and basolateral (Scribble) polarity modules overlap at the apical-lateral border, which, in mammals, is defined by the apical junctional complex (AJC). The AJC is composed of tight junctions (TJ) and adherens junctions (AJ) and plays fundamental roles in epithelial morphogenesis and plasticity. However, the molecular composition and precise sub-junctional organization of the AJC and its associated polarity regulators are not well defined. Here, we used the peroxidase APEX2 for quantitative proximity proteomics (QPP) and electron microscopy (EM) imaging to dissect the architecture of the AJC in fully polarized MDCK-II cells. We present a high-confidence proteome of the apical-lateral border in which TJ and AJ components and apical and lateral compartment markers are spatially resolved. We further demonstrate that the Crumbs complex (Pals1, PatJ, Lin7c, and Crumbs3) defines a hitherto unidentified membrane compartment apical of TJ, which we coin the vertebrate marginal zone (VMZ). QPP, imaging, and immunoprecipitation assays showed that the HOMER scaffolding proteins, PKN2 and PTPN13, and the membrane-proximal HIPPO pathway proteins ARHGAP29 and STXBP4 are recruited to the VMZ via the PDZ domains of PatJ. Taken together, our work defines the spatial and molecular organization of the apical-lateral border in mammalian epithelial cells, reveals an intriguing molecular and spatial conservation of invertebrate and vertebrate cell polarity protein domains, and identifies a VMZ-associated protein network implicated in HIPPO signaling and the control of the cortical actin cytoskeleton. Show less