Elongases of very long-chain fatty acids (Elovls) and fatty acyl desaturases (Fads) are two key enzymes in the biosynthesis of long-chain polyunsaturated fatty acids (LC-PUFAs). Here, we identified and characterized five Elovl genes ( MulElovl2/5 , MulElovl4 , MulElovlc , MulElovl7a , and MulElovl7b ) from the genome of Mulinia lateralis , a potential model bivalve. Expression analysis revealed that MulElovl2/5 , MulElovl4 and MulElovlc were highly expressed during the middle stage of embryonic development, whereas MulElovl7a and MulElovl7b peaked in mid-to-late development before declining. Tissue-specific expression showed that MulElovl2/5 and MulElovl4 were predominantly expressed in the digestive gland. Additionally, we examined the effects of dietary LC-PUFA composition on MulElovls expression by feeding M. lateralis two unialgal diets: Chlorella pyrenoidosa (Cp), rich in linoleic acid (LA, C18:2n-6) and α-linolenic acid (ALA, C18:3n-3), and Platymonas helgolandica (Ph), rich in eicosapentaenoic acid (EPA, C20:5n-3). Notably, MulElovls were significantly upregulated in most tissues of the Cp group, suggesting a compensatory mechanism under LC-PUFA-deficient conditions. Functional assays revealed distinct substrate specificities: MulElovl2/5 elongated C18 and C20 PUFAs, while MulElovl4 and MulElovlc efficiently converted C20 to C22 PUFAs. Additionally, MulFadsB exhibited Δ6 desaturase activity, enabling the conversion of C18 PUFAs. These findings demonstrate that M. lateralis possesses endogenous biosynthetic pathways for arachidonic acid (ARA) from LA via Δ6 desaturation, elongation, and Δ5 desaturation, as well as partial elongation of EPA to C22:5n-3. Our findings provide new insights into a comparison of endogenous LC-PUFAs synthetic capabilities in mollusks and highlight M. lateralis as a valuable model for investigating lipid metabolism in marine bivalves.
Fatty acid desaturases (Fads), as key enzymes in the biosynthesis of long-chain polyunsaturated fatty acids (LC-PUFAs), catalyze the desaturation between defined carbons of fatty acyl chains and control the degree of unsaturation of fatty acids. In the present study, two Fads genes, designatedMulFadsAandMulFadsB, were identified from the genome of the dwarf surf clamMulinia lateralis(Mollusca, Mactridae), and their spatiotemporal expression was examined. MulFadsA and MulFadsB contained the corresponding conserved functional domains and clustered closely with their respective orthologs from other mollusks. Both genes were expressed in the developmental stages and all tested adult tissues ofM. lateralis, withMulFadsAexhibiting significantly higher expression levels in adult tissues thanMulFadsB. Subsequently, the effects of dietary microalgae onFadsexpressions in the dwarf surf clam were investigated by feeding clams with two types of unialgal diets varying in fatty acid content, i.e.,Chlorella pyrenoidosa(Cp) andPlatymonas helgolandica(Ph). The results show that the expressions ofMulFadswere significantly upregulated among adult tissues in the Cp group compared with those in the Ph group. In addition, we observed the desaturation activity of MulFadsA via heterologous expression in yeasts, revealing Δ5 desaturation activity toward PUFA substrates. Taken together, these results provide a novel perspective onM. lateralisLC-PUFA biosynthesis, expanding our understanding of fatty acid synthesis in marine mollusks.
危险品化学品经营许可证（带存储）