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

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: LEC and VEC RNA profiles on sibling and ddx21 mutant cells obtained from zebrafish embryos

具有分化特征与功能的脉管系统发育，需要对细胞命运特化、谱系分化以及血管网络生长进行协同调控。在发育中的血管网络内，细胞增殖受到时空特异性调控，但目前尚不明确该调控的实现路径，以及其在不同谱系中的差异化控制机制。本研究通过对斑马鱼（zebrafish）开展正向遗传筛选（forward genetic screen），筛选能够形成血管却无法生成淋巴管的突变体，最终发现了RNA解旋酶（RNA helicase）Ddx21的突变株。Ddx21以细胞自主性方式调控淋巴管内皮细胞（lymphatic endothelial cells, LEC）的早期发育。Ddx21对于Vegfc-Vegfr3介导的内皮细胞增殖至关重要。Ddx21是公认的核糖体RNA转录调控因子；在Ddx21缺失的情况下，突变淋巴管内皮细胞的核糖体生物发生过程显著减弱。最终，Ddx21的缺失会引发p53-p21依赖的细胞周期阻滞，从而阻断胚胎淋巴管生成。综上，RNA解旋酶Ddx21通过平衡核糖体生物发生与p53-p21信号通路，协同调控内皮细胞对Vegfc-Vegfr3信号的增殖响应。该机制在肿瘤转移、淋巴管畸形等过度淋巴管生成相关疾病中具有潜在治疗价值。实验设计：对取自斑马鱼胚胎的同窝野生型对照与ddx21突变体细胞中的淋巴管内皮细胞（LEC）与血管内皮细胞（vascular endothelial cells, VEC）开展转录组谱分析。