Molecular and Functional Characterization of Elovl4 Genes in Sparus aurata and Solea senegalensis Pointing to a Critical Role in Very Long-Chain (>C24) Fatty Acid Synthesis during Early Neural Development of Fish.

Sofia Morais,Francisco Hontoria,María José Agulleiro,Inma Varó,Juan Carlos Navarro,Miguel Torres,Óscar Monroig

doi:10.3390/ijms21103514

Sofia Morais, Francisco Hontoria + Show 5 more

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https://doi.org/10.3390/ijms21103514

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Abstract

Very long-chain fatty acids (VLC-FA) play critical roles in neural tissues during the early development of vertebrates. However, studies on VLC-FA in fish are scarce. The biosynthesis of VLC-FA is mediated by elongation of very long-chain fatty acid 4 (Elovl4) proteins and, consequently, the complement and activity of these enzymes determines the capacity that a given species has for satisfying its physiological demands, in particular for the correct development of neurophysiological functions. The present study aimed to characterize and localize the expression of elovl4 genes from Sparus aurata and Solea senegalensis, as well as to determine the function of their encoded proteins. The results confirmed that both fish possess two distinct elovl4 genes, named elovl4a and elovl4b. Functional assays demonstrated that both Elovl4 isoforms had the capability to elongate long-chain (C20–24), both saturated (SFA) and polyunsaturated (PUFA), fatty acid precursors to VLC-FA. In spite of their overlapping activity, Elovl4a was more active in VLC-SFA elongation, while Elovl4b had a preponderant elongation activity towards n-3 PUFA substrates, particularly in S. aurata, being additionally the only isoform that is capable of elongating docosahexaenoic acid (DHA). A preferential expression of elovl4 genes was measured in neural tissues, being elovl4a and elovl4b mRNAs mostly found in brain and eyes, respectively.

Highlights

Certain long-chain (C20–24) polyunsaturated fatty acids (LC-PUFA), namely eicosapentaenoic acid (EPA; 20:5n-3), arachidonic acid (ARA; 20:4n-6) and docosahexaenoic acid (DHA; 22:6n-3), are regarded as physiologically essential for the correct development of vertebrates, including fish [1]
Sequence analyses revealed that the investigated predicted elongation of very long-chain fatty acid 4 (Elovl4) proteins contain all the characteristic domains of vertebrate Elovl4 family members [27,28], including the ER retention signal (RXKXX), the histidine box (HXXHH), which is involved in the electron transfer process during fatty acid elongation [4], and other transmembrane domains, to what has been described in other fish species [9,10,11,29,30,31,32,33,34,35]
Phylogenetic analysis confirmed the existence of two isoforms of S. aurata (Sa) and Ss Elovl4, which clustered, together with corresponding Elovl4 orthologs from other teleosts, into different branches, confirming that the described Elovl4 isoforms are true orthologs of the Elovl4a and Elovl4b proteins that are present in teleosts [2]

Summary

Introduction

Certain long-chain (C20–24) polyunsaturated fatty acids (LC-PUFA), namely eicosapentaenoic acid (EPA; 20:5n-3), arachidonic acid (ARA; 20:4n-6) and docosahexaenoic acid (DHA; 22:6n-3), are regarded as physiologically essential for the correct development of vertebrates, including fish [1]. These compounds can be obtained through the diet or, alternatively, biosynthesized from C18 polyunsaturated fatty acids (PUFA), such as α-linolenic acid (18:3n-3) and linoleic acid (18:2n-6), via enzymatic reactions carried out by fatty acyl desaturases (Fads) and elongation of very long-chain fatty acid (Elovl) proteins [1,2]. Elovl is responsible for the production of very long-chain saturated fatty acids (VLC-SFA) [8]

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