Molecular biological and cytological study of the phylogenically unique characters in the acoel Platyhelminthes

1. 采用光镜和扫描电镜对奈开扁虫的发育过程进行了研究。早期细胞谱系得以建立。其劈裂模式是独特的，不同于其他湍流体。在卵裂的最后阶段，卵裂球从动物和植物两端内化。比较了9个湍流群的表面结构。扁虫的表皮细胞和下层的肌肉细胞没有任何基底结构分离，而是彼此直接接触，形成肌肉-表皮复合体。这种结构在阿科尔扁虫中是独特的，在其他被检查的湍流目中没有发现。肌-表皮复合体形成于胚胎早期，在肌-表皮复合体的形成过程中，肌-表皮复合体与肌之间没有基底结构。这一事实表明，肌肉-表皮复合体不是退行性变的结果。比较了7个湍流目线粒体基因CO1和细胞色素b的密码子。扁虫与其他6个涡虫类群的遗传密码存在差异。3 .除扁形虫外的6目中，AAA和ATA分别编码天冬氨酸和异亮氨酸，而在扁形虫中，AAA和ATA编码赖氨酸和蛋氨酸。基于18s核糖体DNA的分子生理学的详细重新分析证实了先前的结果，即在其他涡虫被指定之前，acel扁虫就已经分化了。本项目所获得的结果共同表明，acel扁虫是一种非常独特的动物，属于不同于扁形纲的门。

1. The developmental process in the acoel flatworm Convoluta naikaiensis was examined by light microscopy and scanning electron microscopy. The early cell lineage was established. The cleavage patter was unique and different from those in other turbellarians. In the last of the cleavage stage, blastomeres internalize both from the animal and vegetal ends.2. The surface structures were compared among 9 turbellarian groups. In the acoel flatworm, the epidermal cells and the underlying muscle cells were not separated by any basal structure but were in direct contact with each other, forming a muscle-epidermis complex. This structure was unique in the acoel flatworm, not found in other turbellarian orders examined. The muscle-epidermis complex was formed at an early embryonic stage and the basal structure never appeared between the epidennis and the muscle during the course of the muscle-epidermis complex. This fact suggests that the muscle-epidermis complex does not results from degeneration.3. Mitochondrial codons in the mitochondrial genes (CO1 and cytochrome b ) were compared among 7 turbellarian orders. The genetic code was different between the acoel flatworm and other 6 turbellarian groups. In the 6 orders except the acoel flatworm, AAA and ATA code aspartic acid and isoleucine, respectively, but in the acoel flatworm, AAA and ATA codes lysine and methionine.4. Detailed re-analysis of the molecular phylogy on the basis of the 18s ribosomal DNA confirmed the previous result that the acoel flatworm diverged before other turbellarians were specified.5. The results obtained in the present project collectively suggest that the acoel flatworms are very unique animals belonging to a phylum different from the Platyhelminthes.