Abstract
BackgroundThe 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.ResultsThe 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.ConclusionsDuplications 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.
Highlights
The insulin signaling pathway (ISP) has a key role in major physiological events like carbohydrate metabolism and growth regulation
The D. pulex genome includes 25 putative genes belonging to the insulin signaling pathway, which include all major components of this signaling system
Tyrosine kinase (TK) domain of diverse receptor tyrosine kinase (RTK) and insulin-like receptors (InR) were aligned using MUSCLE 3.7 and the alignments were refined with Gblocks 0.91b which eliminates poorly aligned positions and divergent regions in order to focus on unambiguously aligned residues
Summary
The insulin signaling pathway (ISP) has a key role in major physiological events like carbohydrate metabolism and growth regulation. In humans and higher vertebrates, signaling through the insulin pathway is critical for the regulation of intracellular and blood glucose levels and has a pivotal importance in metabolic diseases, such as diabetes, and cellular process such as ageing [1,2,3]. It is well recognized as a major regulator of growth in both vertebrates and invertebrates and can trigger diapause and regulate ageing in invertebrates [4,5,6,7,8]. The IRR is called an orphan receptor as the ligand and its biological function is still unknown
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