Two Elongases, Elovl4 and Elovl6, Fulfill the Elongation Routes of the LC-PUFA Biosynthesis Pathway in the Orange Mud Crab (Scylla olivacea)

Abstract

While the capacity for long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis has been elucidated in vertebrates and several invertebrate phyla, the comparative knowledge in crustaceans remains vague. A key obstacle in mapping the full spectrum of LC-PUFA biosynthesis in crustacean is the limited evidence of the functional activities of enzymes involved in desaturation or elongation of polyunsaturated fatty acid substrates. In this present study, we report on the cloning and functional characterization of two Elovl elongases from the orange mud crab, Scylla olivacea. Sequence and phylogenetic analysis suggest these two Elovl as putative Elovl4 and Elovl6, respectively. Using the recombinant expression system in Saccharomyces cerevisiae, we demonstrate the elongation capacity for C18-C22 PUFA substrates in the S. olivacea Elovl4. The S. olivacea Elovl6 elongated saturated fatty acids, monounsaturated fatty acids, and interestingly, C18-C20 PUFA. Taken together, both Elovl fulfill the elongation steps required for conversion of C18 PUFA to their respective LC-PUFA products. Elovl4 is expressed mainly in the hepatopancreas and gill tissues, while Elovl6 is predominant in digestive tissues. The mRNA expression of both enzymes was higher in mud crabs fed with vegetable oil-based diets. Tissue fatty acid composition also showed the existence of LC-PUFA biosynthesis intermediate products in tissues expressing these two elongases. In summary, we report here two novel Elovl with PUFA elongating activities in a marine brachyuran. This will contribute significantly to the understanding of the LC-PUFA biosynthesis pathway in crustaceans and advance the development of aquafeed for intensive farming of the mud crab.

Comparative Analyses of Scylla Olivacea Gut Microbiota Composition and Function Suggest the Capacity for Polyunsaturated Fatty Acid Biosynthesis

“…We found lower LC-PUFA content in hepatopancreas and muscle of crab fed diet LOCO or LOCOAB as compared to diet FO. This reiterates previous ndings on the fatty acid pro les of mud crabs fed VO-based diets [77,78]. Therefore, the LC-PUFA biosynthesis activities driven by the in vivo enzymatic capacity of S. olivacea or gut bacterial communities in the VO-based diets are unable to produce tissue deposition levels of LC-PUFA which are comparable to diet FO.…”

“…A complete repertoire of Fads and Elovl for LC-PUFA biosynthesis was only recently shown in a harpacticoid copepod, T. californicus [10]. In decapods, while the presence of functional Elovl has been reported from mud crab Scylla olivacea [11,12] and swimming crab Portunus trituberculatus [13], the actual existence of functional Fads remains contentious [14]. The vastly diversi ed Crustacea subphylum includes the Scylla mudcrabs, which have ecological and economical importance in mangroves of the Indo-Paci c region [15].…”

A complete enzymatic capacity for biosynthesis of docosahexaenoic acid (DHA, 22 : 6n–3) exists in the marine Harpacticoida copepod Tigriopus californicus

“…Interestingly, the T. californicus Elo1, Elo2 and Elo5 grouped with sequences from other copepods, particularly T. japonicus , while the relationship of the T. californicus Elo3 with other copepod genes could not be established (figure 3). Away from the Pancrustacea clade described above, the T. californicus Elo6 clustered within another well-supported clade (89%) containing several Arthropoda sequences including functionally characterized Elovl4-like sequences from two decapods ( S. olivacea and Portunus trituberculatus ) [52,53] (figure 3). The T. californicus Elo4 was grouped in a completely distinct clade that out-grouped all other sequences (figure 3).…”

Long-Read Sequencing Reveals the Repertoire of Long-Chain Polyunsaturated Fatty Acid Biosynthetic Genes in the Purple Land Crab, Gecarcoidea lalandii (H. Milne Edwards, 1837)

“…Similar corresponding works on various aquatic invertebrates such as molluscs and echinoderms have also revealed the presence of Fads and Elovl orthologs and LC-PUFA biosynthesis activities (Monroig and Kabeya, 2018). The presence of functional Elovl in crustaceans were only recently shown in two marine brachyuran crabs (Mah et al, 2019;Sun et al, 2020;Ting et al, 2020). Given the limited amount of LC-PUFA in the terrestrial food chain, very little is known about how terrestrial crustaceans adapt in terms of LC-PUFA biosynthesis capacity.…”

“…Elovl6, Elovl7, ElovlA, Elovl B and the putative new Elovl all shared the common ancestors while the Elovl4 formed a separate clade. To date, the Elovl4 and Elovl6 have been shown to have in vitro PUFA elongation capacities in marine brachyuran species (Sun et al, 2020;Ting et al, 2020). Interestingly, while G. lalandii appear to have a Elovl6 ortholog, there was no Elovl4.…”