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Open Access Research article

Unusual duplication of the insulin-like receptor in the crustacean Daphnia pulex

Philippe Boucher1*, Delphine Ditlecadet2, Caroline Dubé1 and France Dufresne1*

Author Affiliations

1 Université du Québec à Rimouski, Département de Biologie, Centre d'Études Nordiques, 300 Allée des Ursulines, Rimouski, Québec, G5L 4L8 Canada

2 Department of Biology; Memorial University of Newfoundland; St. John's, Newfoundland, A1B 3X9 Canada

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BMC Evolutionary Biology 2010, 10:305  doi:10.1186/1471-2148-10-305

Published: 12 October 2010

Abstract

Background

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.

Results

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.

Conclusions

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.