Combining Foxc2 and Connexin37 deletions in mice leads to severe defects in lymphatic vascular growth and remodeling

Connexins (Cxs), proteins that are vital for intercellular communication in vertebrates, have recently been shown to play a critical role in lymphatic development. However, our knowledge is currently limited regarding the functional relationships of Cxs with other proteins and signaling pathways. Cell culture studies have shown that Cx37 is necessary for coordinated activation of the transcription factor NFATc1, which cooperates with Foxc2 (another transcription factor) during lymphatic endothelial development. These data suggest that Cxs, Foxc2, and NFATc1 are part of a common developmental pathway. Here, we present a detailed characterization of Foxc2^+/-Cx37^-/- mice, demonstrating that lymphatic network architecture and valve formation rely on the concurrent embryonic expression and function of Foxc2 and Cx37. Foxc2^+/-Cx37^-/- mice have lymphedema in utero, exhibit craniofacial abnormalities, show severe dilation of intestinal lymphatics, display abnormal lacteal development, lack lymphatic valves, and typically die perinatally (outcomes not seen in Foxc2^+/- or Cx37^-/- mice separately). We provide a rigorous, quantitative documentation of lymphatic vascular network changes that highlight the specific structural alterations that occur in Foxc2^+/-Cx37^-/- mice. These data provide further evidence suggesting that Foxc2 and Cx37 are elements in a common molecular pathway directing lymphangiogenesis.