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首页> 外文期刊>Cell and Tissue Research >Tight junction formation in early Xenopus laevis embryos: identification and ultrastructural characterization of junctional crests and junctional vesicles
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Tight junction formation in early Xenopus laevis embryos: identification and ultrastructural characterization of junctional crests and junctional vesicles

机译：非洲爪蟾早期胚胎中的紧密连接形成：接合波峰和接合小泡的鉴定和超微结构表征

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How tight junctions (TJ) form during early amphibian embryogenesis is still an open question. We used time-lapse video microscopy, scanning electron microscopy (SEM), TEM and freeze-fracture to gain new insight into TJ biogenesis in early clevages of Xenopus laevis. Video analysis suggests three phases in junction formation between blastomeres. A first “waiting” phase, where new unpigmented lateral membranes are generated. A second “mixing” phase, where the unpigmented lateral membrane is separated from the pigmented apical membrane by an area showing a limited degree of intermingling of cortical pigment. And a third “sealing” phase, characterized by the formation of cingulin-containing boundaries between membrane domains, and their rapid directional adhesion in a zipper-like fashion. By SEM, we characterized these boundaries (“junctional crests”, JC) as arrays of villiform protrusions at the border between old and new membranes. In the 2-cell embryo, JC are deeply located, and thus not visible at the surface, but they become increasingly more superficial as cleavages progress. After adjacent blastomeres have adhered to each other, fractured JC display linear arrays of junctional vesicles (JV) of 1–3 μm diameter. TEM analysis shows that JV are symmetrically located near the apposed membranes of adjacent blastomeres, and that the membranes near the JV display focal sites of intimate contact, typical of TJ. Freeze-fracture analysis confirms that intramembrane fibrils, typical of TJ, are present at adhesion sites. We conclude that TJ are formed following the sealing of JC, through the recruitment, sorting and assembly of membrane and cytoplasmic proteins at or near JV.
机译：在早期两栖动物胚胎发生过程中如何形成紧密连接（TJ）仍是一个悬而未决的问题。我们使用延时视频显微镜，扫描电子显微镜（SEM），TEM和冷冻断裂来获得对非洲爪蟾早期狭窄中TJ生物发生的新见解。视频分析表明卵裂球之间的连接形成分为三个阶段。第一“等待”阶段，其中产生新的未着色的侧膜。第二个“混合”阶段，其中未着色的侧膜与着色的顶膜之间的区域分开，显示出皮质颜料混合程度有限。第三阶段是“密封”阶段，其特征是在膜结构域之间形成了含甘油的边界，并以拉链状的方式迅速定向粘合。通过SEM，我们将这些边界（“结顶”，JC）定性为新旧膜之间边界上的绒毛状突起阵列。在2细胞胚胎中，JC位于深处，因此在表面不可见，但是随着分裂的进行，它们变得越来越肤浅。相邻的卵裂球相互粘附后，断裂的JC会显示直径为1-3μm的结节囊泡（JV）的线性阵列。 TEM分析显示，JV对称地位于相邻卵裂球的并置膜附近，并且JV附近的膜显示出紧密接触的焦点，这是TJ的典型特征。冷冻断裂分析证实，TJ典型的膜内原纤维存在于粘连部位。我们得出的结论是，TJ是在JC密封之后通过在JV或附近的膜和细胞质蛋白的募集，分类和组装而形成的。

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