Fibronectin is required for proper extracellular matrix organization and cardiac outflow tract elongation in

Introduction: Congenital heart defects frequently arise from alterations in cardiac outflow tract (OFT) elongation, a process that depends on the coordinated deployment of second heart field (SHF) progenitor cells and their interactions with the extracellular matrix (ECM). Among ECM components, fibronectin (Fn1) and tenascin-C (TnC) have emerged as key regulators of cardiac morphogenesis; however, the cellular organization of the SHF and the dynamics of its ECM environment remain poorly characterized in externally developing vertebrate models. Methods: Here, we investigated the cellular and extracellular architecture of SHF-associated cells localized to the dorsal pericardial wall (DPW) during heart development in Xenopus laevis using immunofluorescence, three-dimensional reconstructions, quantitative analyses, and functional depletion experiments. Results: We found that SHF-associated cells undergo a stage-dependent transition from a predominantly monolayered organization at NF35 to a multilayered structure at NF42, accompanied by dynamic ECM remodeling characterized by increased expression of Fn1, TnC, and collagen I (Col I), as well as redistribution of ECM components within the DPW. Functional depletion of Fn1 disrupted cardiac morphogenesis, resulting in OFT shortening and reduced ventricular size, while also decreasing TnC and Col I levels without affecting TnC spatial organization within the DPW. Conclusion: Together, these findings support a role for Fn1 in regulating ECM assembly within SHF-associated cells and demonstrate that ECM remodeling contributes to DPW organization during OFT elongation, highlighting Xenopus laevis as a valuable model for studying ECM-driven mechanisms of cardiac morphogenesis.