Franch-Marro Xavier, Martín Nicolás, Averof Michalis, Casanova Jordi
Institut de Biologia Molecular de Barcelona, CSIC, Barcelona, C/Josep Samitier 1-5, 08028 Barcelona, Spain.
Development. 2006 Mar;133(5):785-90. doi: 10.1242/dev.02260.
Adaptation to diverse habitats has prompted the development of distinct organs in different animals to better exploit their living conditions. This is the case for the respiratory organs of arthropods, ranging from tracheae in terrestrial insects to gills in aquatic crustaceans. Although Drosophila tracheal development has been studied extensively, the origin of the tracheal system has been a long-standing mystery. Here, we show that tracheal placodes and leg primordia arise from a common pool of cells in Drosophila, with differences in their fate controlled by the activation state of the wingless signalling pathway. We have also been able to elucidate early events that trigger leg specification and to show that cryptic appendage primordia are associated with the tracheal placodes even in abdominal segments. The association between tracheal and appendage primordia in Drosophila is reminiscent of the association between gills and appendages in crustaceans. This similarity is strengthened by the finding that homologues of tracheal inducer genes are specifically expressed in the gills of crustaceans. We conclude that crustacean gills and insect tracheae share a number of features that raise the possibility of an evolutionary relationship between these structures. We propose an evolutionary scenario that accommodates the available data.
对多样栖息地的适应促使不同动物进化出独特的器官，以便更好地利用其生存环境。节肢动物的呼吸器官便是如此，从陆生昆虫的气管到水生甲壳类动物的鳃。尽管果蝇气管发育已得到广泛研究，但气管系统的起源一直是个长期存在的谜团。在此，我们表明果蝇的气管基板和腿原基源自同一群细胞，它们的命运差异由无翅信号通路的激活状态控制。我们还得以阐明触发腿部特化的早期事件，并表明即使在腹部节段，隐秘的附肢原基也与气管基板相关联。果蝇中气管原基与附肢原基之间的关联让人联想到甲壳类动物中鳃与附肢之间的关联。气管诱导基因的同源物在甲壳类动物的鳃中特异性表达这一发现强化了这种相似性。我们得出结论，甲壳类动物的鳃和昆虫的气管具有许多共同特征，这增加了这些结构之间存在进化关系的可能性。我们提出了一个能解释现有数据的进化假说。
