Hanken J, Hall B K
Department of Environmental, Population, and Organismic Biology, University of Colorado, Boulder 80309-0334.
Anat Embryol (Berl). 1988;178(3):219-27. doi: 10.1007/BF00318225.
We examined the role of thyroid hormone (TH) in mediating cranial ossification during metamorphosis in the Oriental fire-bellied toad, Bombina orientalis. Exogenous T3 (3,3',5-triiodo-L-thyronine) was administered in three treatment dosages (0.025, 0.25, and 2.5 micrograms) plus a control dosage via plastic micropellets implanted within the dermis of tadpoles of three Gosner developmental stages: 28/29, 30/31, 32/33. Tadpoles were recovered after 2, 4, 6, and 8 d, and scored for the presence of three bones - median parasphenoid and paired frontoparietals and exoccipitals--as seen in cleared-and-stained, whole-mount preparations. T3 induced precocious ossification in both a stage-dependent and a dosage-dependent manner; stage dependence corresponded precisely with the degree of osteogenic differentiation at the time of hormone administration. Precocious ossification thus was due to the T3-promoted growth and calcified matrix deposition of these centers. Differential TH sensitivity among osteogenic sites may underlie both the temporal cranial ossification sequences characteristic of metamorphosing amphibians as well as sequence differences commonly observed among taxa.
我们研究了甲状腺激素（TH）在东方铃蟾（Bombina orientalis）变态过程中介导颅骨骨化的作用。通过植入处于三个戈斯纳发育阶段（28/29、30/31、32/33）的蝌蚪真皮内的塑料微丸，以三种治疗剂量（0.025、0.25和2.5微克）外加一个对照剂量给予外源性T3（3,3',5-三碘-L-甲状腺原氨酸）。在2、4、6和8天后取出蝌蚪，并对如透明和染色的整体标本中所见的三块骨头——中轴蝶骨以及成对的额顶骨和枕骨——的存在情况进行评分。T3以阶段依赖性和剂量依赖性方式诱导早熟骨化；阶段依赖性与激素给药时的成骨分化程度精确对应。因此，早熟骨化是由于T3促进了这些中心的生长和钙化基质沉积。成骨部位之间不同的TH敏感性可能是变态两栖动物特有的颅骨骨化时间序列以及不同分类群中常见的序列差异的基础。
