The embryonic development of the triclad Schmidtea polychroa
The embryonic development of the triclad Schmidtea polychroa
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DOI：
10.1007/s00427-004-0455-8
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发表时间：
2005-03-01
影响因子：
2.4
通讯作者：
Romero, R
中科院分区：
文献类型：
--
作者：
Cardona, A;Hartenstein, V;Romero, R
Triclad扁形虫的再生特性得到了很好的研究，但对它们的胚胎发育知之甚少。我们在这里描述的胚胎发育的triclad Schmidtea polychroa，使用组织学和免疫细胞化学分析的整装制剂和部分。在卵裂早期（第1阶段），卵黄细胞融合并将受精卵包裹成合胞体。受精卵分裂成分裂球，分裂球分离并迁移到合胞体中。在第2阶段，一个分裂球的子集分化成一个短暂的胚胎表皮，包围卵黄合胞体，和胚胎咽。其他卵裂球分裂为合胞体中分散的细胞群。在第3阶段，胚胎咽吸收外部卵黄细胞，在合胞体的中心形成胃腔。合胞体的卵黄和其中的卵裂球被压缩成一层薄薄的外壳。两侧对称的腹神经索先驱从靠近胚胎咽的位置向前延伸，咽定义了后极。第4阶段的特征是胚胎细胞的大量增殖。大的充满蛋黄的细胞排列在合胞体上形成胃皮层。在第5阶段，外部的合胞体卵黄套被吸收，其中包含的胚胎细胞分化成肌肉和神经细胞的不规则支架。表皮细胞分化并取代短暂的胚胎表皮。通过阶段6-8，胚胎采用其蠕虫状形状，并且松散分散的分化细胞群体合并成结构上确定的器官。我们的分析揭示了S.多色胚胎发生类似于再生的形态发生事件。
Triclad flatworms are well studied for their regenerative properties, yet little is known about their embryonic development. We here describe the embryonic development of the triclad Schmidtea polychroa, using histological and immunocytochemical analysis of whole-mount preparations and sections. During early cleavage (stage 1), yolk cells fuse and enclose the zygote into a syncytium. The zygote divides into blastomeres that dissociate and migrate into the syncytium. During stage 2, a subset of blastomeres differentiate into a transient embryonic epidermis that surrounds the yolk syncytium, and an embryonic pharynx. Other blastomeres divide as a scattered population of cells in the syncytium. During stage 3, the embryonic pharynx imbibes external yolk cells and a gastric cavity is formed in the center of the syncytium. The syncytial yolk and the blastomeres contained within it are compressed into a thin peripheral rind. From a location close to the embryonic pharynx, which defines the posterior pole, bilaterally symmetric ventral nerve cord pioneers extend forward. Stage 4 is characterized by massive proliferation of embryonic cells. Large yolk-filled cells lining the syncytium form the gastrodermis. During stage 5 the external syncytial yolk mantle is resorbed and the embryonic cells contained within differentiate into an irregular scaffold of muscle and nerve cells. Epidermal cells differentiate and replace the transient embryonic epidermis. Through stages 6-8, the embryo adopts its worm-like shape, and loosely scattered populations of differentiating cells consolidate into structurally defined organs. Our analysis reveals a picture of S. polychroa embryogenesis that resembles the morphogenetic events underlying regeneration.