Isl1-expressing non-venous cell lineage contributes to cardiac lymphatic vessel development

The origin of the mammalian lymphatic vasculature has been studied for more than a century; however, details regarding organ-specific lymphatic development remain unknown. A recent study reported that cardiac lymphatic endothelial cells (LECs) stem from venous and non-venous origins in mice. Here, we identified Isl1 -expressing progenitors as a potential non-venous origin of cardiac LECs. Genetic lineage tracing with Isl1-Cre reporter mice suggested a possible contribution from the Isl1 -expressing pharyngeal mesoderm constituting the second heart field to lymphatic vessels around the cardiac outflow tract as well as to those in the facial skin and the lymph sac. Isl1 + lineage-specific deletion of Prox1 resulted in disrupted LYVE1 + vessel structures, indicating a Prox1-dependent mechanism in this contribution. Tracing back to earlier embryonic stages revealed the presence of VEGFR3 + and/or Prox1 + cells that overlapped with the Isl1 + pharyngeal core mesoderm. These data may provide insights into the developmental basis of heart diseases involving lymphatic vasculature and improve our understanding of organ-based lymphangiogenesis.