Ohmura H, Wakahara M
Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan.
Differentiation. 1998 Sep;63(5):238-46.
Transformation of skin from larval to adult types in a salamander, Hynobius retardatus, which had been reported to show neotenic reproduction in a specific environment, was examined morphologically in normally metamorphosing, precociously metamorphosing and metamorphosis-arrested larvae. Typical larval skin was composed of an epidermis constituted by three types of cells such as apical, Leydig, and basal cells. The Leydig cells were larval specific, and thus disappeared and were replaced by adult epidermal cells during the metamorphosis. Disappearance of the Leydig cells was accomplished by apoptosis as confirmed by the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end-labeling method and electron microscopy during the normal metamorphosis and precocious metamorphosis induced by exogenously applied triiodothyronine. Typical adult skin was composed of epidermis constituted by stratified squamous cells and of dermis mainly occupied with two types of dermal glands, mucous and serous glands. When the metamorphosis was arrested by different procedures (thyroidectomy, hypophysectomy, goitrogen treatment, and rearing at low temperature), the larval-specific Leydig cells fully remained in the epidermis, suggesting that the disappearance of these depended on the thyroid activity. Contrary to this, dermal glands behaved differently from the Leydig cells, though they developed and differentiated from epidermal basal cells and constituted the same skin. Those in the metamorphosis-arrested (thyroidectomized, hypophysectomized, or goitrogen-treated) larvae, except in the larvae reared at 4 degrees C, appeared a little later than in the controls. Thus, the aged, metamorphosis-arrested larvae had skin which consisted of larval type epidermis (Leydig cells) and adult type dermis (mucous and serous glands).
在日本林蛙（Hynobius retardatus）中，已报道其在特定环境下会出现幼态繁殖现象，本研究对正常变态、早熟变态和变态停滞的幼虫进行了形态学检查，观察其皮肤从幼体类型向成体类型的转变。典型的幼体皮肤由表皮构成，表皮由三种类型的细胞组成，即顶端细胞、莱迪希细胞和基底细胞。莱迪希细胞是幼体特有的，因此在变态过程中会消失，并被成体表皮细胞所取代。通过末端脱氧核苷酸转移酶介导的dUTP-生物素缺口末端标记法和电子显微镜证实，在正常变态以及外源性应用三碘甲状腺原氨酸诱导的早熟变态过程中，莱迪希细胞通过凋亡而消失。典型的成体皮肤由分层鳞状细胞构成的表皮和主要由两种真皮腺（粘液腺和浆液腺）占据的真皮组成。当通过不同程序（甲状腺切除、垂体切除、致甲状腺肿物质处理以及低温饲养）使变态停滞时，幼体特有的莱迪希细胞会完全保留在表皮中，这表明这些细胞的消失依赖于甲状腺的活性。与此相反，真皮腺的行为与莱迪希细胞不同，尽管它们由表皮基底细胞发育和分化而来，并构成同一种皮肤。除了在4℃饲养的幼虫外，变态停滞（甲状腺切除、垂体切除或致甲状腺肿物质处理）的幼虫中的真皮腺出现时间比对照组稍晚。因此，老龄的、变态停滞的幼虫的皮肤由幼体类型的表皮（莱迪希细胞）和成体类型的真皮（粘液腺和浆液腺）组成。
