Peterson M D, Popadić A, Kaufman T C
Howard Hughes Medical Institute at Indiana University at Bloomington, Bloomington, IN 47405, USA.
Dev Genes Evol. 1998 Dec;208(10):547-57. doi: 10.1007/s004270050214.
Homologues of the Drosophila segment polarity gene engrailed have been cloned from many insect species, as well as other arthropods and non-arthropods. We have cloned partial cDNAs of two engrailed homologues, which we call engrailed-related genes, from the phylogenetically basal insect, Thermobia domestica (Order Thysanura) and possibly as many as four engrailed-related genes from the phylogenetically intermediate insect, Oncopeltus fasciatus (Order Hemiptera). Previous to our findings, only single engrailed-related homologues had been found in phylogenetically intermediate insect species (Tribolium and Schistocerca) and in the crustacean Artemia, while two engrailed-related homologues have been found in more derived orders (Hymenoptera and the engrailed and invected genes of lepidopterans and dipterans). Consequently, we performed a phylogenetic analysis of insect engrailed-related genes to determine whether insects ancestrally had one or two engrailed-related genes. We have found evidence of concerted evolution among engrailed-related paralogues, however, that masks the true phylogenetic history of these genes; the phylogeny may only be decipherable, therefore, by examining the presence or absence of engrailed-specific and invected-specific motifs, which will require cloning the full length cDNAs from more species. In addition, we examined the embryonic expression pattern of the two Thermobia engrailed-related genes; like Drosophila engrailed and invected, they are expressed in very similar patterns, but show one temporal difference in pregnathal segments that correlates with the tentative phylogenetic placement of the genes. Thermobia engrailed-related expression also confirms that the dorsal ridge is an ancient structure in insects.
果蝇体节极性基因engrailed的同源物已从许多昆虫物种以及其他节肢动物和非节肢动物中克隆出来。我们从系统发育上处于基部的昆虫嗜卷书虱（缨尾目）中克隆了两个engrailed同源物的部分cDNA，我们将其称为engrailed相关基因，并且可能从系统发育处于中间位置的昆虫美洲大草蛉（半翅目）中克隆到了多达四个engrailed相关基因。在我们的发现之前，仅在系统发育处于中间位置的昆虫物种（赤拟谷盗和沙漠蝗）以及甲壳动物卤虫中发现了单个engrailed相关同源物，而在更进化的目（膜翅目以及鳞翅目和双翅目的engrailed和invected基因）中发现了两个engrailed相关同源物。因此，我们对昆虫engrailed相关基因进行了系统发育分析，以确定昆虫在祖先时是有一个还是两个engrailed相关基因。然而，我们发现engrailed相关旁系同源物之间存在协同进化的证据，这掩盖了这些基因的真实系统发育历史；因此，可能只有通过检查engrailed特异性和invected特异性基序的存在与否才能解读系统发育，而这需要从更多物种中克隆全长cDNA。此外，我们研究了嗜卷书虱两个engrailed相关基因的胚胎表达模式；与果蝇的engrailed和invected一样，它们以非常相似的模式表达，但在孕节段显示出一个时间差异，这与这些基因的暂定系统发育位置相关。嗜卷书虱engrailed相关基因的表达也证实了背嵴是昆虫中的一个古老结构。
