The body plan of the cnidarian medusa: distinct differences in positional origins of polyp tentacles and medusa tentacles
The body plan of the cnidarian medusa: distinct differences in positional origins of polyp tentacles and medusa tentacles
复制标题
刺胞动物水母的身体结构：水螅触手和水母触手位置起源的明显差异
作者：
H. Shimizu;H. Namikawa
蛇形动物有两种典型的体型，附着型(水母)和游泳型(水母)(图1)。在柱状体柱的顶端，息肉有一张触须紧紧围绕着它的嘴(图1a)。水母的形态特征是身体像一个倒置的碗，称为伞(图1B)。雨伞的边缘有垂下来的触角(边缘的触角)。伞口位于被称为伞柄的柱状结构的末端，该结构位于伞的中心。尽管在形态上有这些显著的差异，动物学教科书通常都会这样写：“水母是一种倒置的息肉”，这意味着这两种水母的体型基本上是相同的(Ruppert和Barnes 1996)。因此，人们通常认为水母的触角和水母的边缘触角是同源的。然而，教科书的描述是否正确仍是个未知数。根据经典观察和最新的分子研究结果，我们提出了一个简单但新颖的答案，表明线虫属动物在身体上有两个区域形成触角，一个在口端，另一个在动物的流产位置。在这项研究中，我们重点分析了水栖类触角和水母类边缘触角在位置来源上的差异。虽然水母形体存在于三个水母纲(即水母纲、立方体纲和水母纲)，但在这些具有水母阶段的物种中，约75%属于水母纲(布鲁斯卡和布鲁斯卡1990；Boero等人)。1992年；布伊隆和博埃罗2000年)。此外，水母类是目前唯一进行了分子分析的类别，尽管主要针对息肉进行了广泛的基因表达研究。触须这个术语通常用来描述蛇形动物靠近嘴巴张开的灵活的附属物，并参与利用线虫细胞捕捉猎物(Ewer 1947)。如果在水母体内产生的触须显示出发育到水母的连续性，这将直接证明水母的触须和水母的触须本质上是相同的结构。然而，这种连续性看不到。相反，水母的触须是在水母形成过程中新形成的(即水母类中的无性萌芽)。水生动物研究模型--九头蛇属的形态特征是单生的息肉形式，口端的下腹被触须包围，体柱/胃区较大，反口端有柄和脚区(图1C)。九头蛇被认为是这一类典型的孤立性息肉。然而，一些水生动物有息肉，触须出现在两个区域。一种水生动物科(图1D)的水生动物，其触须一目了然地集中在口腔末端，这表明该动物的形态与九头蛇基本相似。然而，这种观点是完全错误的。海蛇的消化区(由DR表示)，由于消化的食物含量而呈粉红色，约占体柱长度的3/4，而其余的(约1/4)对应于花梗区域(图1C)。相比之下，珊瑚状息肉的消化区位于两个触角环之间，仅占身体的约1/10。息肉的其余部分(约9/10)由花梗区域(图1D)占据，表明两个息肉的身体部分具有不同的比例，看起来相似的圆柱形形态。因此，珊瑚状息肉的次生触角环的位置对应于位于动物流产侧的消化区和脚节区之间的边界。由于珊瑚虫的次级触角环位于动物消化区的背面，所以次级环上的触须应该被认为是反面触角。这意味着在珊瑚状息肉中有两个触角区域，一个在消化区域的口侧，另一个在该区域的反面。应该指出的是，这两个区域的触角以合作的方式参与捕获猎物。当水生动物的三个亚纲(水母亚纲、珊瑚亚纲和细水母亚纲)进化和发展时11：6,619-621(2009)
Cnidarians have two typical body forms, the attached form (polyp) and the swimming form (medusa) (Fig. 1). The polyp has a mouth with tentacles closely surrounding it at the apical end of a cylindrical body column (Fig. 1A). The morphology of a medusa is characterized by a body like an inverted bowl, termed the umbrella (Fig. 1B). The umbrella has tentacles hanging down from its margin (marginal tentacles). The mouth is located at the end of a columnar structure termed the manubrium, which is located at the center of the umbrella. Despite these significant differences in morphology, zoology textbooks typically state that ‘‘the medusa is the upside down form of a polyp,’’ implying that the two forms have basically the same body plan (Ruppert and Barnes 1996). As a result, it has generally been assumed that the tentacles of the polyp and the marginal tentacles of the medusa are homologous. However, it remains unknown whether the textbooks’ description is correct or not. Based upon classical observations and recent results of molecular studies, we present a simple but novel answer to this question by showing that animals that belong to Cnidaria have two areas in the body where tentacles are formed, one at the oral end, and the other in an aboral location on the animal. We focused our analysis on the differences in positional origins of hydropolyp tentacles and hydromedusa marginal tentacles in this study. Although the medusa form occurs in three cnidarian classes (viz., Scyphozoa, Cubozoa, and Hydrozoa), of these about 75% of the species that have the medusa stage belong to Hydrozoa (Brusca and Brusca 1990; Boero et al. 1992; Bouillon and Boero 2000). Furthermore, Hydrozoa is currently the only class where molecular analysis has been performed, although extensive gene expression studies have been carried out mostly with polyps. The term tentacle is generally used to describe the flexible appendages that are located near the mouth opening in cnidarians and are involved in capturing prey using nematocytes (Ewer 1947). If a tentacle produced in the polyp showed developmental continuity into the medusa, this would be direct evidence that the polyp tentacles and the medusa tentacles are essentially the same structure. This continuity, however, is not seen. Instead, medusa tentacles are newly formed during the process of medusa formation (namely, asexual budding in Hydrozoa). The morphology ofHydra, a hydrozoan research model, is characterized by the solitary polyp form with the hypostome surrounded by tentacles at the oral end, a large body column/ gastric region, and with the peduncle and foot region at the aboral end (Fig. 1C). Hydra has been considered to represent the typical solitary polyp form of this class. However, some hydrozoans have polyps in which tentacles emerge in two regions. A polyp of the hydrozoan family Corymorphidae (Fig. 1D) has tentacles that are at a glance concentrated at the oral end, suggesting that the morphology of the animal is basically similar to Hydra. This view is, however, entirely erroneous. The digestive region (denoted by DR) of a hydra polyp, which is pink in color because of digested food content, occupies about 3/4 of the body column length, whereas the rest (about 1/4) corresponds to the peduncle region (Fig. 1C). In contrast, the digestive region of a corymorphid polyp is the region that lies between the two tentacle rings occupying only about 1/10 of the body. The rest of the polyp (about 9/10) is occupied by the peduncle region (Fig. 1D), demonstrating that the two polyps have different proportions of the body parts in apparently similar cylindrical morphology. Therefore, the position of the secondary tentacle ring of the corymorphid polyp corresponds, in a hydra polyp, to the boundary between the digestive region and the peduncle region, which is located on the aboral side of the animal. Because the secondary tentacle ring of the corymorphid polyp is located aboral to the digestive region of the animal, the tentacles in the secondary ring should be considered aboral tentacles. This implies that there are two tentacle regions in the corymorphid polyp, one on the oral side of the digestive region and the other in the aboral side of this region. It should be noted that the tentacles in the two regions are involved in capturing prey in a cooperative manner. When three subclasses of Hydrozoa (Limnomedusae, Anthmedusae [Athecata], and Leptomedusae [Thecata]) are EVOLUTION & DEVELOPMENT 11:6, 619 –621 (2009)
Otx2 基因表达的尾部限制作为中脑/后脑边界的标记：一项使用原位杂交和小鸡/鹌鹑同位移植的研究。
DOI：
10.1242/dev.122.12.3785
发表时间：
1996
期刊：
Development (Cambridge, England)
影响因子：
--
作者：
Millet,S;Bloch-Gallego,E;Simeone,A;Alvarado-Mallart,RM
通讯作者：
Alvarado-Mallart,RM