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Cell lineage analysis of the mandibular segment of the amphipod Orchestia cavimana reveals that the crustacean paragnaths are sternal outgrowths and not limbs.
Frontiers in Zoology ( IF 2.8 ) Pub Date : 2006-12-06 , DOI: 10.1186/1742-9994-3-19
Carsten Wolff 1 , Gerhard Scholtz
Affiliation  

The question of arthropod head segmentation has become one of the central issues in Evolutionary Developmental Biology. The number of theories pertaining to head segments progressively enlarges, old concepts have been revitalized, and nearly every conceivable composition of the arthropod head has at some point received discussion. One contentious issue involves a characteristic mouthpart in crustaceans--the lower lips or the so-called paragnaths. The paragnaths build the posterior border of the mouth region antagonistic to the upper lip--the labrum. We show here the development of the appendage-like structures in the mandibular region of the amphipod crustacean Orchestia cavimana at a high level of cellular resolution. The embryos are examined during development of the mouthparts using in vivo labeling. An invariant cell division pattern of the mandibular segment was detected by 4D-microscopy and a preliminary model for pattern of the first cleavages in the mandibular region created. With this indispensable precondition single ectodermal cells of the grid-like pattern were labeled with DiI--a lipophilic fluorescent dye--to trace cell lineages and determine the clonal composition of the developing mouthparts, especially the mandibular segment. From our data it is evident that the paragnaths are sternal outgrowths of the mandible segment. The assumption of the limb nature of paragnaths and the presence of an additional head segment between the mandibular and the second antennal segments are clearly refuted by our data. Our results show the power of cell lineage and clonal analyses for inferences on the nature, origin and thus homology of morphological structures. With this kind of investigation morphological and gene expression data can be complemented. We discuss notable similarities of paragnath anlagen to those of the hypopharynx complex in myriapods and hexapods. The fact that both structures grow out as two lateral buds in the same region of the mandibular sternite during development, and their important role in the formation of the feeding apparatus as a highly specialized chewing chamber in adults of crustaceans, myriapods, and hexapods argue for the paragnaths/hypopharynx anlagen being an additional potential apomorphy of Mandibulata.

中文翻译:

对两栖类Orchestia cavimana下颌节的细胞谱系分析表明,甲壳类旁颌骨是胸骨生长而不是四肢。

节肢动物的头部分割问题已成为进化发育生物学的核心问题之一。与头部有关的理论数目逐渐增多,旧观念得到了振兴,节肢动物头部的几乎每一个可以想到的组成都在某个时候受到了讨论。一个有争议的问题涉及甲壳类动物的典型口器-下唇或所谓的paragnaths。颚状棘突建立了与上唇对立的唇区后边界。我们在这里显示了在两栖类甲壳动物Orchestia cavimana的下颌区域的附属物结构的高细胞分辨率发展情况。使用体内标记在口器发育过程中检查胚胎。通过4D显微镜检测下颌节段的不变细胞分裂模式,并创建下颌区域首次分裂模式的初步模型。利用这种必不可少的前提条件,将具有格子状图案的单个外胚层细胞用亲脂性荧光染料DiI标记,以追踪细胞谱系并确定发育中的口器(尤其是下颌节)的克隆组成。从我们的数据中可以明显看出,截瘫是下颌骨的胸骨长出。我们的数据清楚地驳斥了准直器的肢体性质的假设以及下颌骨和第二触角之间存在额外的头部。我们的结果显示了细胞谱系和克隆分析对自然界进行推断的能力,起源,因此是形态结构的同源性。通过这种调查,可以补充形态学和基因表达数据。我们讨论了在无足类和六足类动物中,paragnath anlagen与下咽复合体的显着相似性。这两个结构在发育过程中都在下颌骨的同一区域中作为两个侧芽长出,这一事实以及它们在甲壳纲动物,无足动物和六足动物的成虫中作为高度专业化的咀嚼室的形成中的重要作用都证明了这一点。腮腺/下咽anlagen是下颌骨的另一种潜在的无性。我们讨论了在无足类和六足类动物中,paragnath anlagen与下咽复合体的显着相似性。这两个结构在发育过程中都在下颌骨的同一区域中作为两个侧芽长出,这一事实以及它们在甲壳纲动物,无足动物和六足动物的成虫中作为高度专业化的咀嚼室的形成中的重要作用都证明了这一点。腮腺/下咽anlagen是下颌骨的另一种潜在的无性。我们讨论了在无足类和六足类动物中,paragnath anlagen与下咽复合体的显着相似性。这两个结构在发育过程中都在下颌骨的同一区域中作为两个侧芽长出,这一事实以及它们在甲壳纲动物,无足动物和六足动物的成虫中作为高度专业化的咀嚼室的形成中的重要作用都证明了这一点。腮腺/下咽anlagen是下颌骨的另一种潜在的无性。
更新日期:2019-11-01
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