Ishizuya-Oka A, Ueda S, Damjanovski S, Li Q, Liang V C, Shi Y B
Department of Histology and Neurobiology, Dokkyo University School of Medicine, Tochigi, Mibu, 321-02, Japan.
Dev Biol. 1997 Dec 1;192(1):149-61. doi: 10.1006/dbio.1997.8749.
To determine whether the remodeling of the well-organized intestinal epithelium during amphibian metamorphosis is regionally regulated along the anteroposterior axis of the intestine, we raised a polyclonal antibody against the Xenopus laevis intestinal fatty acid-binding protein (IFABP), which is known to be specifically expressed in intestinal absorptive cells, and examined immunohistochemically the differentiation, proliferation, and apoptosis of the epithelial cells throughout X. laevis small intestine. During pre- and prometamorphosis, IFABP-immunoreactive (ir) epithelial cells were localized only in the anterior half of the larval intestine. At the beginning of metamorphic climax, apoptotic cells detected by nick end-labeling (TUNEL) suddenly increased in number in the entire larval epithelium, concurrently with the appearance of adult epithelial primordia. Subsequently, the adult primordia in the anterior part of the intestine developed more rapidly by active cell proliferation than those in the posterior part, and replaced the larval epithelial cells earlier than those in the posterior part. IFABP-ir cells in the adult epithelium were first detectable at the tips of newly formed folds in the proximal part of the intestine. Thereafter, IFABP expression gradually progressed both in the anteroposterior direction and in the crest-trough direction of the folds. These results suggest that developmental processes of the adult epithelium in the X. laevis intestine are regionally regulated along the anteroposterior axis of the intestine, which is maintained throughout metamorphosis, and along the trough-crest axis of the epithelial folds, which is newly established during metamorphosis. Furthermore, the regional differences in IFABP expression along the anteroposterior axis of the intestine were reproduced in organ cultures in vitro. In addition, IFABP expression was first down-regulated and then reactivated in vitro when the anterior part, but not the posterior part, of the larval intestine was treated with thyroid hormone (TH) for extended periods. Therefore, it seems that, in addition to TH, an endogenous factor(s) localized in the intestine itself with an anteroposterior gradient participates in the development of the adult epithelium during amphibian metamorphosis.
为了确定两栖动物变态发育过程中结构良好的肠道上皮重塑是否沿肠道前后轴受到区域调节，我们制备了一种针对非洲爪蟾肠道脂肪酸结合蛋白（IFABP）的多克隆抗体，已知该蛋白在肠道吸收细胞中特异性表达，并通过免疫组织化学方法检测了非洲爪蟾整个小肠上皮细胞的分化、增殖和凋亡情况。在变态前和变态初期，IFABP免疫反应性（ir）上皮细胞仅定位于幼体肠道的前半部分。在变态高峰期开始时，通过缺口末端标记（TUNEL）检测到的凋亡细胞在整个幼体上皮中的数量突然增加，同时出现了成体上皮原基。随后，肠道前部的成体原基通过活跃的细胞增殖比后部发育得更快，并比后部更早地取代了幼体上皮细胞。成体上皮中的IFABP-ir细胞首先在肠道近端新形成的皱襞顶端被检测到。此后，IFABP表达在前后方向以及皱襞的嵴-谷方向上逐渐进展。这些结果表明，非洲爪蟾肠道中成体上皮的发育过程沿肠道前后轴受到区域调节，该轴在整个变态过程中保持不变，并且沿上皮皱襞的谷-嵴轴受到区域调节，该轴在变态过程中重新建立。此外，在体外器官培养中再现了IFABP沿肠道前后轴表达的区域差异。此外，当幼体肠道的前部而非后部长期用甲状腺激素（TH）处理时，IFABP表达在体外首先被下调，然后重新激活。因此，似乎除了TH之外，一种以前后梯度形式定位于肠道自身的内源性因子在两栖动物变态发育过程中参与了成体上皮的发育。
