Université du Québec à Rimouski, Département de Biologie, Centre d'Études Nordiques, 300 Allée des Ursulines, Rimouski, Québec, G5L 4L8 Canada.
BMC Evol Biol. 2010 Oct 12;10:305. doi: 10.1186/1471-2148-10-305.
The insulin signaling pathway (ISP) has a key role in major physiological events like carbohydrate metabolism and growth regulation. The ISP has been well described in vertebrates and in a few invertebrate model organisms but remains largely unexplored in non-model invertebrates. This study is the first detailed genomic study of this pathway in a crustacean species, Daphnia pulex.
The Daphnia pulex draft genome sequence assembly was scanned for major components of the ISP with a special attention to the insulin-like receptor. Twenty three putative genes are reported. The pathway appears to be generally well conserved as genes found in other invertebrates are present. Major findings include a lower number of insulin-like peptides in Daphnia as compared to other invertebrates and the presence of multiple insulin-like receptors (InR), with four genes as opposed to a single one in other invertebrates. Genes encoding for the Dappu_InR are likely the result of three duplication events and bear some unusual features. Dappu_InR-4 has undergone extensive evolutionary divergence and lacks the conserved site of the catalytic domain of the receptor tyrosine kinase. Dappu_InR-1 has a large insert and lacks the transmembranal domain in the β-subunit. This domain is also absent in Dappu_InR-3. Dappu_InR-2 is characterized by the absence of the cystein-rich region. Real-time q-PCR confirmed the expression of all four receptors. EST analyses of cDNA libraries revealed that the four receptors were differently expressed under various conditions.
Duplications of the insulin receptor genes might represent an important evolutionary innovation in Daphnia as they are known to exhibit extensive phenotypic plasticity in body size and in the size of defensive structures in response to predation.
胰岛素信号通路（ISP）在碳水化合物代谢和生长调节等主要生理事件中起着关键作用。该通路在脊椎动物和少数无脊椎动物模式生物中已有详细描述，但在非模式无脊椎动物中仍未得到广泛研究。本研究是首次对甲壳动物溞属（Daphnia pulex）中该通路进行详细的基因组研究。
本研究对 ISP 的主要成分进行了 Daphnia pulex 草案基因组序列组装扫描，特别关注胰岛素样受体。报告了 23 个假定基因。该通路似乎普遍得到了很好的保守，因为在其他无脊椎动物中发现了该通路的基因。主要发现包括与其他无脊椎动物相比，溞属中的胰岛素样肽数量较少，以及存在多个胰岛素样受体（InR），而其他无脊椎动物中只有一个基因。编码 Dappu_InR 的基因可能是三次复制事件的结果，并具有一些不寻常的特征。Dappu_InR-4 经历了广泛的进化分歧，并且缺乏受体酪氨酸激酶催化结构域的保守位点。Dappu_InR-1 具有较大的插入片段，并且在β亚基中缺乏跨膜结构域。该结构域也不存在于 Dappu_InR-3 中。Dappu_InR-2 的特征是缺乏富含半胱氨酸的区域。实时 q-PCR 证实了所有四个受体的表达。cDNA 文库的 EST 分析表明，在各种条件下，四个受体的表达不同。
胰岛素受体基因的复制可能是溞属的一个重要进化创新，因为它们已知在体型和防御结构大小方面表现出广泛的表型可塑性，以应对捕食。
