Watanabe Yusuke, Tanaka Rumi, Kobayashi Hisao, Utoh Rie, Suzuki Ken-Ichi, Obara Masanobu, Yoshizato Katsutoshi
Developmental Biology Laboratory, Department of Biological Science, Graduate School of Science, Hiroshima University, Higashihiroshima, Hiroshima, Japan.
Dev Dyn. 2002 Dec;225(4):561-70. doi: 10.1002/dvdy.10196.
Anuran larvae transform their epidermis to the adult counterpart during metamorphosis. The major event of this process is the proliferation of larval epidermal basal cells and their differentiation into adult ones. The present study isolated novel type I keratin cDNA dubbed xak-c (Xenopus adult keratin-c) that was exclusively expressed in adult epidermal basal cells. The gene started its expression in the larval epidermis at the onset of metamorphosis. Thyroid hormone (TH) induced the precocious expression of the gene in the epidermis of premetamorphic tadpoles. To study the transcriptional regulation of this gene in relation to epidermal metamorphosis, a 2.8 kb 5'-flanking region of xak-c was cloned and its promoter activity was investigated. Gene constructs were made so as to contain the xak-c promoter region and gene of EGFP or luciferase as a reporter gene and were transfected into various types of cells, which revealed that the 5'-flanking region had an epidermal cell-specific transcriptional activity in both anurans and mammals. Larval skin tissues of Xenopus were transfected with the constructs and cultured in the presence and absence of TH, which showed that the promoter region is responsive to TH, although the region did not contain the consensus TH response element-like sequence. In sharp contrast, the promoter region did not respond to TH in the adult skin, clearly indicating that the cloned region contains specific sequences that respond to metamorphosis-dependent transcription factor(s).
无尾两栖类幼体在变态过程中将其表皮转变为成体表皮。这一过程的主要事件是幼体表皮基底细胞的增殖及其分化为成体细胞。本研究分离出一种新型的I型角蛋白cDNA，命名为xak-c（非洲爪蟾成体角蛋白-c），它仅在成体表皮基底细胞中表达。该基因在变态开始时在幼体表皮中开始表达。甲状腺激素（TH）诱导该基因在变态前蝌蚪的表皮中提前表达。为了研究该基因与表皮变态相关的转录调控，克隆了xak-c的2.8 kb 5'侧翼区域并研究了其启动子活性。构建了基因载体，使其包含xak-c启动子区域和作为报告基因的EGFP或荧光素酶基因，并将其转染到各种类型的细胞中，结果表明该5'侧翼区域在无尾两栖类和哺乳动物中均具有表皮细胞特异性转录活性。用构建体转染非洲爪蟾的幼体皮肤组织，并在有和没有TH的情况下进行培养，结果表明启动子区域对TH有反应，尽管该区域不包含共有TH反应元件样序列。与之形成鲜明对比的是，该启动子区域在成体皮肤中对TH无反应，这清楚地表明克隆区域包含对变态依赖性转录因子有反应的特定序列。
