Vieira, J. M. | bioRxiv Science

bioRxiv2020

The extracellular matrix protein agrin is essential for epicardial epithelial-to-mesenchymal transition during heart development

During embryonic heart development, epicardial cells residing within the outer layer of the heart undergo epithelial-mesenchymal transition (EMT) and migrate into the myocardium to support and stimulate organ growth and morphogenesis. Disruption of epicardial EMT results in aberrant heart formation and embryonic lethality. Despite being an essential process during development, the regulation of epicardial EMT is poorly understood. Here we report EMT on the epicardial surface of the embryonic heart at subcellular resolution using scanning electron microscopy (SEM). We identified high- and low-EMT regions within the mesothelial layer of the epicardium and an association with key components of the extracellular matrix (ECM). The ECM basement membrane-associated proteoglycan agrin was found to localize in the epicardium in regions actively undergoing EMT. Deletion of agrin resulted in impaired EMT and compromised development of the epicardium, accompanied by down-regulation of the epicardial EMT regulator WT1. Agrin enhanced EMT in human embryonic stem cell-derived epicardial-like cells by decreasing {beta}-catenin and promoting pFAK localization at focal adhesions. In addition, agrin promoted the aggregation of its receptor dystroglycan to the Golgi apparatus in murine epicardial cells and loss of agrin resulted in dispersal of dystroglycan throughout the epicardial cells in embryos, disrupting basement membrane integrity and impairing EMT. Our results provide new insights into the role of the ECM in heart development, and implicate agrin as a critical regulator of EMT, functioning to ensure dystroglycan connects signals between the ECM and activated epicardial cells. Summary statementThe basement membrane-associated proteoglycan agrin regulates epicardial epithelia-to-mesenchyme transition (EMT) through dystroglycan localizing on the Golgi apparatus. This ensures ECM and cytoskeletal connectivity and mechanical integrity of the transitioning epicardium and has important implications for the role of the extracellular matrix (ECM) in heart development.

developmental biology↗

bioRxiv2020

Tissue-resident macrophages regulate lymphatic vessel growth and patterning in the developing heart

Macrophages are components of the innate immune system with key roles in tissue inflammation and repair. It is now evident that macrophages also support organogenesis, but few studies have characterized their identity, ontogeny and function during heart development. Here, we show that resident macrophages in the subepicardial compartment of the developing heart coincide with the emergence of new lymphatics and interact closely with the nascent lymphatic capillaries. Consequently, global macrophage-deficiency led to extensive vessel disruption with mutant hearts exhibiting shortened and mis-patterned lymphatics. The origin of cardiac macrophages was linked to the yolk sac and fetal liver. Moreover, Csf1r+ and Cx3cr1+ myeloid sub-lineages were found to play essential functions in the remodeling of the lymphatic endothelium. Mechanistically, macrophage hyaluronan was found to be required for lymphatic sprouting by mediating direct macrophage-lymphatic endothelial cell interactions. Together, these findings reveal insight into the role of macrophages as indispensable mediators of lymphatic growth during the development of the mammalian cardiac vasculature.Summary statement Tissue-resident macrophages are indispensable mediators of lymphatic vessel formation during heart development and function to remodel the vascular plexus.View Full Text

developmental biology↗