The RNA helicase Ddx21 controls Vegfc-driven developmental lymphangiogenesis by balancing endothelial cell ribosome biogenesis and p53-p21 signalling [human]

The development of a differentiated and functional vasculature requires coordinated control of cell fate specification, lineage differentiation and vascular network growth. Cellular proliferation is spatiotemporally regulated in developing vessel networks but how this is achieved and differentially controlled in specific lineages is unknown. Using a zebrafish forward genetic screen for mutants that form blood vessels but fail to form lymphatic vessels, we uncovered a mutant for the RNA helicase Ddx21. Ddx21 cell-autonomously regulates the early development of lymphatic endothelial cells. Ddx21 is essential for Vegfc-Vegfr3 driven endothelial cell proliferation. Ddx21 is an established regulator of ribosomal RNA transcription and in the absence of Ddx21, mutant lymphatic endothelial cells show reduced ribosome biogenesis. Ultimately, loss of Ddx21 leads to a p53-p21 dependent cell cycle arrest that blocks embryonic lymphangiogenesis. Thus, the RNA helicase Ddx21 coordinates the endothelial cell proliferative response to Vegfc-Vegfr3 signalling by balancing ribosome biogenesis and p53-p21 signalling. This mechanism may have therapeutic potential in diseases of excessive lymphangiogenesis such as in cancer metastasis or lymphatic malformation. Overall design: HUVEC RNA-seq data on untreated control cells and DDX21-siRNA knockdown cells using two constructs