Distinct roles of the Lyve1 lineage in mouse heart development

The genetic mouse model Lyve1 Cre is widely used to study lymphatic endothelial cells, but its activity in the embryonic heart has not been comprehensively defined. Here we show that the Lyve1 lineage contributes to multiple cardiovascular cell types, including venous endothelium of the sinus venosus forming coronary vessels, endocardial cells generating complementary coronary territories and valve structures, lymphatic endothelial cells required for cardiac lymphatic development, and tissue-resident macrophages within the embryonic myocardium. Functional perturbations studies show that Notch1 gain-of-function in Lyve1 + lineages disrupts vascular development, whereas Prox1 deletion causes severe edema, blood-filled lymphatics, and perinatal lethality. Mid-gestation mutants exhibit underdeveloped blood-filled lymphatics despite intact blood vasculature, and by late gestation cardiac lymphatics are largely depleted. These findings reveal distinct cardiovascular roles of the Lyve1 lineage and establish Lyve1 Cre as a versatile but non-specific model, underscoring the need for careful interpretation when investigating heart development and regeneration.