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首页> 外文期刊>Cell and Tissue Research >Dicyemid's dilemma: structure versus genes. The unorthodox structure of dicyemid reproduction.
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Dicyemid's dilemma: structure versus genes. The unorthodox structure of dicyemid reproduction.

机译：Dicyemid的困境：结构与基因。双麦酰胺繁殖的非正统结构。

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The clear phylogenetic status of the enigmatic Phylum Dicyemida is still uncertain. Their primitive body plan lacks essential metazoan synapomorphies, while genetic data favor a kinship with higher lophotrochozoans. This ultrastructural study increases the confusion about this phylum by presenting an unusual gonad and sperm structure lacking all synapomorphies essential for the various phyla of the lophotrochozoans, either free-living ones or parasites. In Dicyema typus, gonadogenesis is reduced to a single somatic cell, i.e., the infusorigen's axial cell that functions as a somatic gonadal founder cell as soon as a spermatogonium takes residence in its cytoplasm. The spermiogenic cells resulting therefrom are not connected by intercellular bridges and permanently contain a bundle of microtubules in their cytoplasm, obviously a kind of dormant develop so-called polycomplexes, multiple synaptinemal complexes. The structure of the sperm is based on a certain kind of somatic cell that has been minimally adapted to function as a sperm. The mature sperm consists in only three organelles: an ovoid nucleus with a somatic chromatin structure, numerous pore complexes and a centrally arranged cluster of coiled tubular structures; a bundle of microtubules embedded into a rim running along the nucleus longitudinal surface, projecting out of the cell like a spear; and a lipid vesicle tightly attached to one pole of the nucleus, touching there the adjacent bundle of microtubules. Immunelectron microscopy confirms the somatic condition of mature sperm, revealing somatic histone H1 immunoreactivity over the nucleus, which can be interpreted as synapomorphy shared with Protozoa, Porifera and Cnidaria. Fertilization occurs as selfing, where the sperm penetrates, "bundle of microtubules first", a primary oocyte attached vis-a-vis on the other side of the plasma membrane of the infusorigen's axial cell. This somatic situation points to an ancient evolutionary model rather than to a condition caused by retrogression due to their life as commensals.
机译：神秘的Phylum Dicyemida的明确的系统发育状态仍不确定。他们原始的身体计划缺乏必要的后生动物同种异型，而遗传数据则支持具有较高滋养体的亲缘关系。这项超微结构研究通过呈现一种不寻常的性腺和精子结构，缺乏对滋养体的各种门（无论是自由生活的还是寄生虫的）必需的所有同形异型体，加剧了对这种门的困惑。在Dicyema typus中，性腺一旦被精子寄居于其细胞质中，就将性腺机能减低为单个体细胞，即，输液素原的轴性细胞起着体细胞性腺基础细胞的作用。由此产生的生精细胞没有通过细胞间桥连接，并且在其细胞质中永久地包含一束微管，显然是一种休眠发育的所谓的多复合物，多种突触复合物。精子的结构基于某种类型的体细胞，该体细胞已被最小化地用作精子。成熟的精子仅由三个细胞器组成：具有体细胞染色质结构的卵圆形核，大量的孔复合体和盘绕的管状结构的中心排列簇。一束微管，嵌在沿细胞核纵向表面延伸的边缘中，像长矛一样突出到细胞外;脂质囊泡紧紧地附着在细胞核的一个极点上，并与相邻的微管束接触。免疫电子显微镜证实了成熟精子的体细胞状况，揭示了细胞核上的体细胞组蛋白H1免疫反应性，这可以解释为与原生动物，孔虫和猪唇草共有的突触。受精过程是自交，精子穿透，“首先是微管束”，一个原代卵母细胞，与输注素原的轴向细胞质膜的另一侧相对。这种躯体情况指向一种古老的进化模型，而不是由于它们作为纪念物而因退步而导致的状况。

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