Department of Entomology, Waters Hall, Kansas State University, Manhattan, KS 66506, USA.
J Insect Physiol. 2011 Sep;57(9):1190-7. doi: 10.1016/j.jinsphys.2011.05.011. Epub 2011 Jun 15.
Crustacean cardioactive peptide (CCAP) is a nonapeptide originally isolated from the shore crab, Carcinus maenas, based on its cardioacceleratory activity. This peptide is highly conserved in insects and other arthropods. In insects CCAP also has an essential role in ecdysis behavior. We previously identified two homologous genes, ccapr-1 and ccapr-2, encoding putative CCAP receptors in the red flour beetle, Tribolium castaneum. In contrast, some insects, including Drosophila melanogaster, carry only one gene encoding a CCAP receptor. Phylogenetic analysis of putative CCAP receptor orthologs reveals a number of independent gene duplications in several insect lineages. In this study, we confirmed that CCAP activates both putative T. castaneum receptors in a heterologous expression system. RNA interference (RNAi) of ccapr-1 and ccapr-2 revealed that ccapr-2 is essential for eclosion behavior in T. castaneum, while RNAi for ccapr-1 did not result in any abnormal phenotype. In vivo cardioacceleratory activity of exogenously applied CCAP was abolished by RNAi of ccapr-2, but not by that of ccapr-1. Thus, only ccapr-2 mediates the cardioacceleratory function, ccapr-1 having apparently lost both functions for eclosion behavior and for cardioacceleration since the recent gene duplication event.
甲壳动物心脏活性肽 (CCAP) 是一种九肽，最初从岸蟹（Carcinus maenas）中分离出来，基于其心脏加速活性。这种肽在昆虫和其他节肢动物中高度保守。在昆虫中，CCAP 也在蜕皮行为中发挥着重要作用。我们之前在红粉甲虫（Tribolium castaneum）中鉴定了两个同源基因，ccapr-1 和 ccapr-2，它们编码假定的 CCAP 受体。相比之下，一些昆虫，包括黑腹果蝇（Drosophila melanogaster），只携带一个基因编码 CCAP 受体。假定的 CCAP 受体同源物的系统发育分析揭示了几个昆虫谱系中存在许多独立的基因重复。在这项研究中，我们证实 CCAP 在异源表达系统中激活了两个假定的 T. castaneum 受体。ccapr-1 和 ccapr-2 的 RNA 干扰（RNAi）表明，ccapr-2 对于 T. castaneum 的蜕皮行为是必需的，而 ccapr-1 的 RNAi 则没有导致任何异常表型。体外给予的 CCAP 的心脏加速活性通过 ccapr-2 的 RNAi 而被废除，但不是通过 ccapr-1 的 RNAi。因此，只有 ccapr-2 介导心脏加速功能，ccapr-1 显然在最近的基因重复事件后失去了蜕皮行为和心脏加速的两种功能。
