A New Conserved Player in Lymphatic Morphogenesis.
A New Conserved Player in Lymphatic Morphogenesis.
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淋巴形态发生中的新保守参与者。
DOI：
10.1161/circresaha.117.310861
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发表时间：
2017
影响因子：
20.1
通讯作者：
Lawson,NathanD
中科院分区：
文献类型：
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作者：
Lawson,NathanD
Lawson Polydom在淋巴发育1217和mRNA中证实了淋巴缺陷是由于svep1功能丧失所致。与此同时，Morooka等人应用基因组编辑技术在斑马鱼svep1中产生了定向缺失，这导致了胸腔导管形成的相同缺陷，进一步证实了淋巴发育中对该基因的需求。对斑马鱼突变表型的更仔细的评估表明，早期的淋巴规范没有受到影响，Prox1在大静脉的祖细胞中有明显的表达，尽管这些淋巴祖细胞的萌发是缺陷的。与VEGFC或其受体Flt4的缺失相关的表型要温和得多，这表明Svep1的作用不依赖于这一途径。事实上，在svep1突变体的淋巴祖细胞中，VEGFC下游重要效应器丝氨酸/苏氨酸激酶ERK的激活没有改变。11两组在svep1基因敲除小鼠中也观察到相似的表型。关口实验室以前的工作已经确定Svep1是整合素-α9β112的高亲和力配体，这表明它可能在淋巴瓣的形成中发挥作用，因此他们有兴趣确定它在淋巴发育中的功能作用。在缺乏svep1的小鼠中，两组都出现了严重的水肿和出生后早期死亡，这表明存在淋巴缺陷。因此，svep1基因缺陷的小鼠胚胎在皮肤的淋巴管模式上显示出缺陷，尽管来自大静脉的淋巴祖细胞的早期规格看起来是正常的，类似于斑马鱼的研究结果。肠系膜淋巴管分析显示集合管形成失败，没有瓣膜。两组在许多不同的解剖位置，包括肠和心脏，都进行了类似的观察，表明svep1在淋巴成熟和瓣膜形态发生中具有全球需求。综上所述，这些观察表明，svep1对于淋巴祖细胞的初始指定是必要的，但在淋巴管成熟和瓣膜形成的后期阶段是必需的。这两篇论文的一个惊人发现是，svep1不是由内皮细胞表达的，而是在密切相关的内皮周围细胞中发现的。利用重组细菌人工染色体介导的斑马鱼转基因，Karpanen等人观察到svep1表达细胞存在于淋巴祖细胞附近，因为它们来自大静脉。随着淋巴管形态发生的进展，这些细胞与淋巴管内皮细胞保持密切联系。Morooka et AL10在斑马鱼和小鼠身上也进行了类似的观察，在后一种情况下使用LacZ敲击等位基因，以及内源性Svep1蛋白的免疫染色。这两组人都无法确定这些细胞的身份，尽管它们似乎不是神经细胞或肌肉细胞。有趣的是，ccbe1(胶原和钙结合的EGF结构域包含蛋白1)，同样是通过对斑马鱼淋巴突变体的正向遗传筛选而被鉴定出来的，也被认为是以一种非内皮细胞自主的方式需要的，并且在发育中的淋巴系统附近的细胞中表达。13从目前的研究来看，ccbe1和svep1是否在同一人群中表达尚不清楚。然而，这些观察表明，存在一种重要的内皮周围支持细胞，这可能是形成早期淋巴管系统所特需的。
Lawson Polydom in Lymphatic Development 1217 well as mRNA, confirmed that lymphatic defects were because of loss of svep1 function. In parallel, Morooka et al10 applied genome editing to generate a targeted deletion in zebrafish svep1, which led to the same defects in thoracic duct formation, further confirming the requirement for this gene in lymphatic development. More careful assessment of the mutant phenotype in zebrafish revealed that early lymphatic specification was unaffected, with Prox1 expression apparent in progenitors in the cardinal vein, although sprouting of these lymphatic progenitors was deficient. This phenotype was much milder that that associated with loss of Vegfc or its receptor, Flt4, suggesting that Svep1 acts independently of this pathway. Indeed, activation of the serine/threonine kinase ERK, an important downstream effector of Vegfc, was not changed in the lymphatic progenitors of svep1 mutants. 11Similar phenotypes were observed by both groups in svep1 knockout mice as well. Previous work from the Sekiguchi Laboratory had identified Svep1 as a high-affinity ligand for the integrin-α9β112, suggesting that it may play a role in lymphatic valve formation, hence their interest in determining its functional role in lymphatic development. In mice lacking svep1, both groups noted severe edema and early postnatal death suggestive of lymphatic defects. Accordingly, svep1-deficient mouse embryos displayed defects in lymphatic patterning in the skin, although early specification of lymphatic progenitors from the cardinal vein appeared normal, similar to results from the zebrafish studies. Analysis of mesenteric lymphatics revealed a failure to form collecting ducts and absence of valves. Similar observations were made by both groups in many different anatomic locations, including the intestine and heart, suggesting a global requirement for svep1 in lymphatic maturation and valve morphogenesis. Together, these observations suggested that svep1 is dispensable for initial specification of lymphatic progenitors but is required at later stages during lymphatic maturation and valve formation. A striking finding made in both papers is that svep1 was not expressed by endothelial cells but was rather found in a closely associated periendothelial cell. Using recombinant bacterial artificial chromosome–mediated transgenesis in zebrafish, Karpanen et al11 observed that svep1-expressing cells were present in the vicinity of lymphatic progenitors because they arose from the cardinal vein. These cells remained in close association with lymphatic endothelial cells as lymphatic morphogenesis proceeded. Similar observations were made by Morooka et al10 in both zebrafish and in mice, using a lacZ knockin allele in the latter case, as well as immunostaining of endogenous Svep1 protein. Neither group was able to definitively determine the identity of these cells, although they did not seem to be neural or muscle cells. Interestingly, ccbe1 (collagen and calcium-binding EGF domain-containing protein 1), which was likewise identified through forward genetic screening for lymphatic mutants in zebrafish, is also known to be required in a nonendothelial cell autonomous manner and is expressed in cells adjacent to the developing lymphatic system. 13 Whether ccbe1 and svep1 are expressed in the same population is not clear from the present studies. However, these observations suggest the existence of an important periendothelial support cell that may be specifically required to pattern the early lymphatic vasculature.