Murine Notch1 is required for lymphatic vascular morphogenesis during development

BACKGROUND

The transmembrane receptor Notch1 is a critical regulator of arterial differentiation and blood vessel sprouting. Recent evidence shows that functional blockade of Notch1 and its ligand, Dll4, leads to postnatal lymphatic defects in mice. However, the precise role of the Notch signaling pathway in lymphatic vessel development has yet to be defined. Here we show the developmental role of Notch1 in lymphatic vascular morphogenesis by analyzing lymphatic endothelial cell (LEC)-specific conditional Notch1 knockout mice crossed with an inducible Prox1CreER(T2) driver.

RESULTS

LEC-specific Notch1 mutant embryos exhibited enlarged lymphatic vessels. The phenotype of lymphatic overgrowth accords with increased LEC sprouting from the lymph sacs and increased filopodia formation. Furthermore, cell death was significantly reduced in Notch1-mutant LECs, whereas proliferation was increased. RNA-seq analysis revealed that expression of cytokine/chemokine signaling molecules was upregulated in Notch1-mutant LECs isolated from E15.5 dorsal skin, whereas VEGFR3, VEGFR2, VEGFC, and Gja4 (Connexin 37) were downregulated.

CONCLUSIONS

The lymphatic phenotype of LEC-specific conditional Notch1 mouse mutants indicates that Notch activity in LECs controls lymphatic sprouting and growth during development. These results provide evidence that similar to postnatal and pathological lymphatic vessel formation, the Notch signaling pathway plays a role in inhibiting developmental lymphangiogenesis.

Alk3/Alk3b and Smad5 mediate BMP signaling during lymphatic development in zebrafish

Lymphatic vessels are essential to regulate interstitial fluid homeostasis and diverse immune responses. A number of crucial factors, such as VEGFC, SOX18, PROX1, FOX2C, and GJC2, have been implicated in differentiation and/or maintenance of lymphatic endothelial cells (LECs). In humans, dysregulation of these genes is known to cause lymphedema, a debilitating condition which adversely impacts the quality of life of affected individuals. However, there are no currently available pharmacological treatments for lymphedema, necessitating identification of additional factors modulating lymphatic development and function which can be targeted for therapy. In this report, we investigate the function of genes associated with Bone Morphogenetic Protein (BMP) signaling in lymphatic development using zebrafish embryos. The knock-down of BMP type II receptors, Bmpr2a and Bmpr2b, and type I receptors, Alk3 and Alk3b, as well as SMAD5, an essential cellular mediator of BMP signaling, led to distinct lymphatic defects in developing zebrafish. Therefore, it appears that each constituent of the BMP signaling pathway may have a unique function during lymphatic development. Taken together, our data demonstrate that BMP signaling is essential for normal lymphatic vessel development in zebrafish.