Chanoine C, Janmot C, Guyot-Lenfant M, Durand J P, d'Albis A, Gallien C L
Laboratoire de Biologie du Développement, UA 1188 C.N.R.S., Université René Descartes, Paris.
Reprod Nutr Dev (1980). 1988;28(3B):721-31.
In the urodelan amphibian Pleurodeles waltlii, spontaneous external metamorphosis was correlated with an increase in the serum level of thyroxine (T4). Within the same period, a change occurred in the myofibrillar ATPase profile of the dorsal skeletal muscle; fibres of larval type were gradually replaced by transitional fibres (type IIC), then by adult fibres of the types I, IIA, and IIB. Likewise, a myosin isoenzymic transition was observed. In larval animals, myosin electrophoresis revealed 3 bands corresponding with isoforms having identical heavy chains (MHC), but different light chains (MLC). In the course of metamorphosis, the 3 larval isomyosins were replaced by 3 isoforms having the adult type MHC and different motility. In a related neotenic species, Ambystoma mexicanum, no spontaneous anatomic metamorphosis occurred; at the time it should theoretically take place, the serum T4 level remained low. The ATPase profile was modified, but transitional fibres that replaced the initial larval types appeared to be persistent, and adult fiber types appeared only in a small amount. Myosin isoenzymic transition was also incomplete, larval isoforms were still distinguished in the neotenic adults. Similar persistence of larval characters was observed in adult Proteus anguinus, a perennibranch that never undergoes anatomical metamorphosis. Experimental hypothyroidian Pleurodeles waltlii displayed no external metamorphosis, only the larval fibre types and isomyosins were detected in those animals. External metamorphosis was induced in Ambystoma mexicanum by a triiodothyronine treatment. A complete myosin isoenzymic transition was observed in metamorphosed animals. These results tend to indicate that a moderate increase in the level of thyroid hormones is sufficient to determine the production of the adult type MHC molecules and the differentiation of the corresponding myofibrillar types in the skeletal dorsal muscle of amphibians, while a marked increase would be necessary for repressing the initial larval feature.
在有尾两栖动物肋突螈中，自发的外部变态与血清甲状腺素（T4）水平的升高相关。在同一时期，背部骨骼肌的肌原纤维ATP酶谱发生了变化；幼虫型纤维逐渐被过渡性纤维（IIC型）取代，然后被I型、IIA型和IIB型的成体纤维取代。同样，观察到肌球蛋白同工酶的转变。在幼虫动物中，肌球蛋白电泳显示出3条带，对应于具有相同重链（MHC）但不同轻链（MLC）的同工型。在变态过程中，3种幼虫异肌球蛋白被3种具有成体类型MHC和不同运动性的同工型所取代。在相关的幼态延续物种墨西哥钝口螈中，没有发生自发的解剖学变态；在理论上应该发生变态的时候，血清T4水平仍然很低。ATP酶谱发生了改变，但取代最初幼虫类型的过渡性纤维似乎持续存在，而成体纤维类型只出现少量。肌球蛋白同工酶的转变也不完全，在幼态延续的成体中仍可区分出幼虫同工型。在终生保持幼体特征、从不经历解剖学变态的洞螈成体中也观察到了类似的幼虫特征持续存在的情况。实验性甲状腺功能减退的肋突螈没有表现出外部变态，在这些动物中只检测到幼虫型纤维和异肌球蛋白。通过三碘甲状腺原氨酸处理诱导墨西哥钝口螈发生外部变态。在变态后的动物中观察到完全的肌球蛋白同工酶转变。这些结果倾向于表明，甲状腺激素水平的适度升高足以决定两栖动物背部骨骼肌中成年型MHC分子的产生和相应肌原纤维类型的分化，而显著升高对于抑制最初的幼虫特征是必要的。
