Molecular Cloning, Functional Characterization and Promoter Analysis of the Snakehead Fish (Channa Sp.) Elongase

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Date
2015-06
Authors
KUAH, MENG KIAT
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Abstract
In order to understand the molecular aspects of long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis capability in a carnivorous freshwater fish, two elongase genes were cloned from the striped snakehead and designated as elovl5 and elovl4-like elongases. All characteristic features of a microsomal fatty acyl elongase were found on the amino acid sequences of both striped snakehead elovl elongases, and they shared high sequence identities with other fish counterparts. Striped snakehead Elovl5 protein exhibited high elongation activities towards C18 and C20 PUFA substrates. It also demonstrated higher preferences towards n-3 PUFA than n- 6 PUFA. Unlike other typical Elovl4 proteins, the striped snakehead Elovl4-like protein is capable in converting C18 PUFA substrates but displayed very low elongation activities towards 22:5n-3 and 22:4n-6 substrates. Despite their similar elongation preferences towards the C18 PUFA, both elovl5 and elovl4-like transcripts possessed distinct profiles of tissue distribution and regulated by dietary PUFA differently. In addition, the putative 2.5 kb promoter region of elovl5 gene was cloned and functionally characterized to identify the transcription factor that was involved in the regulation of the gene transcription. In silico analysis of the promoter region of elovl5 gene revealed the presence of a putative binding site for Srebp proteins. By using dual luciferase assays and EMSA, striped snakehead elovl5 elongase was confirmed as a target gene for the zebrafish Srebp1 protein. Moreover, elovl5 promoter was fused to a GFP reporter gene and its in vivo promoter activity was located to the yolk syncytial layer of developing zebrafish embryos. In summary, the present study showed that striped snakehead is possible to synthesize LC-PUFA de novo from C18 precursors with its well-functioning elongases and the transcriptional regulation of its elovl5 gene is conserved with the mammalian counterparts.
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Molecular Cloning , Snakehead Fish (Channa Sp.) Elongase
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