Distinct roles of the Lyve1 lineage in heart development

Lyve1Cre 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 demonstrated that Notch1 gain-of-function in Lyve1+ lineages disrupted vascular development, while Prox1 deletion caused severe edema, blood-filled lymphatics, and perinatal lethality. Mid-gestation mutants exhibited underdeveloped, blood-filled lymphatics despite intact blood vasculature, and by late gestation cardiac lymphatics were depleted. These findings reveal distinct cardiovascular roles of the Lyve1 lineage and establish Lyve1Cre as a versatile but non-specific tool, underscoring the need for careful interpretation when investigating heart development and regenerative processes.