Kuratani S, Ueki T, Hirano S, Aizawa S
Department of Morphogenesis, Institute of Molecular Embryology and Genetics, Kumamoto University School of Medicine, Japan.
Dev Dyn. 1998 Jan;211(1):35-51. doi: 10.1002/(SICI)1097-0177(199801)211:1<35::AID-AJA4>3.0.CO;2-8.
The effect of all-trans retinoic acid on embryogenesis was studied in a cyclostome, Lampetra japonica. Treatment with 0.05-0.5 microM retinoic acid on early gastrula and early neurula resulted in loss of the pharynx and in the rostral truncation of the neural tube. The mouth, pharynx, esophagus, heart, endostyle, and rostral brain were missing with graded severity. In the severest case, the embryo consisted only of trunk segments, especially myotomes that extended to the rostral end of the axis. The effect appeared to be dose- and stage-dependent: Rostral pharyngeal arches were more vulnerable to a lower amount of retinoic acid, and earlier treatment resulted in severer defects. The initial protrusion of the anterior axis started equally in control and retinoic acid-treated embryos, implying that the head morphogenesis is omitted in treated embryos. By identifying the number of myotomes based on the differentiation of hypobranchial muscles, there seemed to be no myotomes lost by retinoic acid-induced truncation. The rostral truncation, therefore, was not simply a limitation of the anterior axis but was restricted to the ventral portion; only the branchial arches disappeared with normally developing myotomes dorsally. The absent region can be defined as the vertebrate head in a morphological sense, including the branchiomeric and preotic paraxial regions as well as the heart. The results suggest the presence of distinct programs between somitomeric and branchiomeric portions of the body, providing a developmental basis for the dual-metamerical body plan of vertebrates.
在一种圆口纲动物——日本七鳃鳗中研究了全反式维甲酸对胚胎发育的影响。在原肠胚早期和神经胚早期用0.05 - 0.5微摩尔的维甲酸处理，导致咽部缺失以及神经管头部截断。口、咽、食管、心脏、内柱和脑前部缺失，且严重程度不同。在最严重的情况下，胚胎仅由躯干节段组成，特别是延伸到轴前端的肌节。这种影响似乎具有剂量和阶段依赖性：前咽弓对较低剂量的维甲酸更敏感，且早期处理会导致更严重的缺陷。在对照胚胎和经维甲酸处理的胚胎中，前轴的初始突出开始情况相同，这意味着在处理过的胚胎中头部形态发生被省略。通过根据鳃下肌的分化来确定肌节的数量，似乎没有因维甲酸诱导的截断而丢失肌节。因此，头部截断并非仅仅是前轴的限制，而是局限于腹侧部分；只有鳃弓消失，而背侧的肌节正常发育。从形态学意义上讲，缺失的区域可被定义为脊椎动物的头部，包括鳃弓和耳前轴旁区域以及心脏。结果表明身体的体节部分和鳃弓部分之间存在不同的发育程序，为脊椎动物的双体节身体结构提供了发育基础。
