Boucaut J C, Clavilier L, Darribère T, Delarue M, Riou J F, Shi D L
Biologie Moléculaire et Cellulaire du Développement, Groupe Biologie Expérimentale, URA CNRS, Université Pierre et Marie Curie, Paris, France.
Int J Dev Biol. 1996 Aug;40(4):675-83.
Embryogenesis implies a strict control of cell interaction and cell migration. The spatial and temporal regulation of morphogenetic movements occurring during gastrulation is directly dependent on the early cell interactions that take place in the blastula. The newt Pleurodeles waltl is a favorable model for the study of these early morphogenetic events. The combination of orthotopic grafting and fluorescent lineage tracers has led to precise early gastrula mesoderm fate maps. It is now clear that there are no sharp boundaries between germ layers at the onset of gastrulation but rather diffuse transition zones. The coordination of cell movements during gastrulation is closely related to the establishment of dorsoventral polarity. Ventralization by U.V. irradiation or dorsalization by lithium treatment modifies the capacity for autonomous migration on the fibronectin coated substratum of marginal zone cells accordingly. It is now firmly established that mesodermal cells need to adhere to a fibrillar extracellular matrix (ECM) to undergo migration during gastrulation. Extracellular fibrils contain laminin and fibronectin (FN). Interaction of cells with ECM involves receptors of the beta 1 integrin family. A Pleurodeles homolog of the alpha v integrin subunit has been recently identified. Protein alpha v expression is restricted to the surface of mesodermal cells during gastrulation. Integrin-mediated interactions of cells with FN are essential for ECM assembly and mesodermal cell migration. Intracellular injection of antibodies to the cytoplasmic domain of beta 1 into early cleavage embryos causes inhibition of FN fibril formation. Intrablastocoelic injections of several probes including antibodies to FN or integrin alpha 5 beta 1, competitive peptides to the major cell binding site of FN or the antiadhesive protein tenascin all block mesodermal cell migration. This results in a complete arrest of gastrulation indicating that mesodermal cell migration is a major driving force in urodele gastrulation. It is now possible to approach the role of fibroblast growth factor (FGF) during cell interactions taking place in urodele embryos. Four different FGF receptors (FGFR) have been cloned in Pleurodeles. Each of them has a unique mRNA expression pattern. FGFR-1, FGFR-3, and the variant of FGFR-2 containing the IIIb exon are maternally expressed and might be involved in mesodermal induction. During gastrulation, FGFR-3 and FGFR-4 have a restricted pattern of expression, whereas FGFR-1 mRNA is nearly uniformly distributed. Splicing variants FGFR-2IIIb and FGFR-2IIIc have exclusive expression patterns during neurulation. IIIb is expressed in epidermis and IIIc in neural tissue, suggesting a function in the differentiation of ectodermal derivatives.
胚胎发生意味着对细胞间相互作用和细胞迁移的严格控制。原肠胚形成过程中发生的形态发生运动的时空调节直接依赖于囊胚期发生的早期细胞间相互作用。蝾螈（Pleurodeles waltl）是研究这些早期形态发生事件的理想模型。原位移植和荧光谱系示踪剂的结合已绘制出精确的早期原肠胚中胚层命运图谱。现在很清楚，在原肠胚形成开始时，胚层之间没有明显的界限，而是存在弥散的过渡区。原肠胚形成过程中细胞运动的协调与背腹极性的建立密切相关。紫外线照射导致腹化或锂处理导致背化会相应地改变边缘区细胞在纤连蛋白包被基质上自主迁移的能力。现在已经确定，中胚层细胞在原肠胚形成过程中迁移时需要附着于纤维状细胞外基质（ECM）。细胞外纤维包含层粘连蛋白和纤连蛋白（FN）。细胞与ECM的相互作用涉及β1整合素家族的受体。最近已鉴定出αv整合素亚基的蝾螈同源物。蛋白质αv的表达在原肠胚形成期间仅限于中胚层细胞表面。整合素介导的细胞与FN的相互作用对于ECM组装和中胚层细胞迁移至关重要。向早期分裂胚胎的细胞质结构域内注射针对β1的抗体可抑制FN纤维的形成。向囊胚腔注射多种探针，包括针对FN或整合素α5β1的抗体、针对FN主要细胞结合位点的竞争性肽或抗黏附蛋白腱生蛋白，均会阻断中胚层细胞迁移。这导致原肠胚形成完全停滞，表明中胚层细胞迁移是有尾两栖类动物原肠胚形成的主要驱动力。现在有可能探究成纤维细胞生长因子（FGF）在蝾螈胚胎细胞间相互作用中的作用。在蝾螈中已克隆出四种不同的FGF受体（FGFR）。它们各自具有独特的mRNA表达模式。FGFR-1、FGFR-3以及包含IIIb外显子的FGFR-2变体是母源表达的，可能参与中胚层诱导。在原肠胚形成期间，FGFR-3和FGFR-4具有受限的表达模式，而FGFR-1 mRNA几乎均匀分布。剪接变体FGFR-2IIIb和FGFR-2IIIc在神经胚形成期间具有排他性的表达模式。IIIb在表皮中表达，IIIc在神经组织中表达，这表明其在表皮衍生物分化中发挥作用。
