Fritsch Martin, Richter Stefan
Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstraße 43, 10115, Berlin, Germany.
Universität Rostock, Allgemeine und Spezielle Zoologie, Institut für Biowissenschaften, Universitätsplatz 2, 18055, Rostock, Germany.
Dev Genes Evol. 2017 Jul;227(4):289-296. doi: 10.1007/s00427-017-0586-3. Epub 2017 Jul 18.
In terms of morphology, crustacean maxillipeds are hybrid appendages. They arise in anterior thoracic segments and display characteristics of both locomotory (thoracic) and feeding (gnathal) appendages. Maxillipeds are functionally integrated with the anterior gnathal appendages. Hox gene expression patterns and immunolabeling with the FP6.87 antibody, which detects conserved epitopes of UBX and ABD-A proteins, reveal that maxillipeds are consistently associated with a shift in the expression of the homeotic gene Ubx. Ubx transcription products or proteins only appear in thoracic segments with a typical locomotory thoracopod and are consistently absent in the maxilliped. This pattern is found in various crustaceans: the copepod Mesocyclops, the mysid Mysidium, the decapods Homarus and Periclimenes, the isopod Porcellio, and the amphipod Parhyale. In Parhyale, which possesses maxillipeds on the first thoracic segment, gene manipulation experiments have shown that a leg-like thoracic appendage can be recovered by mis-expressing Ubx in that segment and walking legs can be transformed into maxillipeds by Ubx-knockdown. This survey focuses on the expression of UBX/ABD-A proteins, studied using the FP6.87 antibody, in the larval stages of the mystacocarid crustacean Derocheilocaris remanei. Mystacocarids inhabit the intertidal meiofauna zone of sandy beaches and possess one pair of maxillipeds on the first thoracic segment. Strong UBX/ABD-A expression in the developing maxilliped makes Derocheilocaris unique among crustaceans. Our data might also show that the transformation from locomotory thoracopod to maxilliped cannot be accounted for by the mere presence or absence of UBX, because in mystacocarids, UBX is present in both kinds of limbs. The role of the other Hox gene known to be involved in this transformation, Sex combs reduced (Scr), is unclear. The results presented here may document a new example of a shift in Hox gene function in arthropods. The difference in UBX/ABD-A expression between D. remanei and the copepod maxillipeds is of particular interest because correspondences between the feeding apparatus-including the maxilliped-in mystacocarids and copepods have been suggested as being of phylogenetic significance.
从形态学角度来看，甲壳类动物的颚足是混合附肢。它们出现在胸部前段，兼具运动性（胸部）附肢和摄食性（颚部）附肢的特征。颚足在功能上与前部的颚部附肢整合在一起。Hox基因表达模式以及使用FP6.87抗体进行的免疫标记（该抗体可检测UBX和ABD - A蛋白的保守表位）显示，颚足始终与同源异型基因Ubx表达的变化相关。Ubx转录产物或蛋白仅出现在具有典型运动性胸足的胸部节段中，而在颚足中始终不存在。这种模式在多种甲壳类动物中都有发现：桡足类的中剑水蚤、糠虾类的 Mysidium、十足类的龙虾和蝉蟹、等足类的鼠妇以及端足类的Parhyale。在Parhyale中，第一胸节上有颚足，基因操作实验表明，在该节段错误表达Ubx可以恢复类似腿的胸附肢，而敲除Ubx则可将步足转变为颚足。本研究聚焦于使用FP6.87抗体研究的UBX/ABD - A蛋白在神秘虾类甲壳动物德氏神秘虾幼虫阶段的表达。神秘虾类栖息在沙滩潮间带小型底栖动物区，在第一胸节上有一对颚足。发育中的颚足中强烈的UBX/ABD - A表达使德氏神秘虾在甲壳类动物中独具特色。我们的数据还可能表明，从运动性胸足到颚足的转变不能仅由UBX的存在或缺失来解释，因为在神秘虾类中，两种附肢中都存在UBX。已知参与这种转变的另一个Hox基因——性梳减少基因（Scr）的作用尚不清楚。此处呈现的结果可能记录了节肢动物中Hox基因功能转变的一个新例子。德氏神秘虾和桡足类颚足之间UBX/ABD - A表达的差异特别值得关注，因为神秘虾类和桡足类中包括颚足在内的摄食器官之间的对应关系被认为具有系统发育意义。
