Hashimoto S, Fumagalli G, Zanini A, Meldolesi J
Department of Pharmacology, University of Milan, Italy.
J Cell Biol. 1987 Oct;105(4):1579-86. doi: 10.1083/jcb.105.4.1579.
The distribution of three proteins discharged by regulated exocytosis--growth hormone (GH), prolactin (PRL), and secretogranin II (SgII)--was investigated by double immunolabeling of ultrathin frozen sections in the acidophilic cells of the bovine pituitary. In mammotrophs, heavy PRL labeling was observed over secretory granule matrices (including the immature matrices at the trans Golgi surface) and also over Golgi cisternae. In contrast, in somatotrophs heavy GH labeling was restricted to the granule matrices; vesicles and tubules at the trans Golgi region showed some and the Golgi cisternae only sparse labeling. All somatotrophs and mammotrophs were heavily positive for GH and PRL, respectively, and were found to contain small amounts of the other hormone as well, which, however, was almost completely absent from granules, and was more concentrated in the Golgi complex, admixed with the predominant hormone. Mixed somatomammotrophs (approximately 26% of the acidophilic cells) were heavily positive for both GH and PRL. Although admixed within Golgi cisternae, the two hormones were stored separately within distinct granule types. A third type of granule was found to contain SgII. Spillage of small amounts of each of the three secretory proteins into granules containing predominantly another protein was common, but true intermixing (i.e., coexistence within single granules of comparable amounts of two proteins) was very rare. It is concluded that in the regulated pathway of acidophilic pituitary, cell mechanisms exist that cause sorting of the three secretory proteins investigated. Such mechanisms operate beyond the Golgi cisternae, possibly at the sites where condensation of secretion products into granule matrices takes place.
通过对牛垂体嗜酸性细胞超薄冰冻切片进行双重免疫标记，研究了通过调节性胞吐作用分泌的三种蛋白质——生长激素（GH）、催乳素（PRL）和分泌粒蛋白II（SgII）的分布情况。在催乳素细胞中，在分泌颗粒基质（包括反式高尔基体表面的未成熟基质）以及高尔基体潴泡上均观察到强烈的PRL标记。相比之下，在生长激素细胞中，强烈的GH标记仅限于颗粒基质；反式高尔基体区域的囊泡和小管有一些标记，而高尔基体潴泡只有稀疏标记。所有生长激素细胞和催乳素细胞分别对GH和PRL呈强阳性，并且还发现含有少量的另一种激素，然而，这种激素几乎完全不存在于颗粒中，并且在高尔基体复合体中更集中，与主要激素混合存在。混合性生长催乳素细胞（约占嗜酸性细胞的26%）对GH和PRL均呈强阳性。尽管两种激素在高尔基体潴泡中混合，但它们分别储存在不同类型的颗粒中。发现第三种类型的颗粒含有SgII。三种分泌蛋白中的每一种少量溢入主要含有另一种蛋白的颗粒中是常见的，但真正的混合（即两种蛋白相当数量共存于单个颗粒中）非常罕见。得出的结论是，在嗜酸性垂体的调节途径中，存在导致所研究的三种分泌蛋白进行分选的细胞机制。这种机制在高尔基体潴泡之外起作用，可能在分泌产物浓缩成颗粒基质的部位。
