Tice L W, Carter R L, Cahill M C
Tissue Cell. 1977;9(3):395-417. doi: 10.1016/0040-8166(77)90002-7.
The development of tight junctions in fetal rat thyroid from the sixteenth to the twentieth days of gestation was examined with conventional ultrastructural methods and freeze-fracture preparations. These results were compared with those obtained using lanthanum hydroxide and horseradish peroxidase (HRP) tracers. Tight junctions appear to arise on the plasma membranes of fetal thyroid cells by the aggregation and fusion of linear particle chains which appear at several discrete sites on the plasma membrane of developing follicular cells. Tracer studies show that they are effective barriers to the passage of HRP from the outset, are freely penetrated by La3+ at the sixteenth and seventeenth days of gestation, but progressively lose permeability to La3+ from the seventeenth to twentieth days of gestation. However, freeze-fracture observations suggest that La3+ must penetrate into the follicular lumen through the tight junction elements, for the follicular lumen, when it appears, is always completely surrounded by a continuous though sometimes rudimentary meshwork of tight junction elements. The results suggest that the tight junction forms an effective barrier to the passage of large macromolecules, e.g. thyroglobulin, from very early stages in its development. The La3+ results suggest that decreased resistance of the intercellular pathway, possibly related to the development of transepithelial potentials, may occur during this period in development.
利用传统的超微结构方法和冷冻断裂技术，研究了妊娠第16至20天胎鼠甲状腺紧密连接的发育情况。将这些结果与使用氢氧化镧和辣根过氧化物酶（HRP）示踪剂获得的结果进行了比较。紧密连接似乎是由线性颗粒链的聚集和融合在胎儿甲状腺细胞质膜上形成的，这些线性颗粒链出现在发育中的滤泡细胞的质膜上的几个离散位点。示踪剂研究表明，它们从一开始就是HRP通过的有效屏障，在妊娠第16和17天时可被La3+自由穿透，但从妊娠第17天到第20天对La3+的通透性逐渐降低。然而，冷冻断裂观察表明，La3+必须通过紧密连接元件进入滤泡腔，因为滤泡腔出现时，总是完全被紧密连接元件的连续但有时不完整的网络所包围。结果表明，紧密连接从其发育的早期阶段就对大分子（如甲状腺球蛋白）的通过形成了有效的屏障。La3+的结果表明，在此发育阶段，细胞间途径的阻力可能与跨上皮电位的发育有关，可能会降低。
