Characteristics of the fads2 gene promoter in marine teleost Epinephelus coioides and role of Sp1-binding site in determining promoter activity

Abstract

Δ6 fatty acyl desaturase (Fads2) is a rate-limiting enzyme in long-chain polyunsaturated fatty acids (LC-PUFA) biosynthesis. Comparative analysis of gene promoters of Fads2 between salmonids and carnivorous marine fish suggested that the lack of binding site for stimulatory protein 1 (Sp1) was responsible for the low expression of fads2 gene of carnivorous marine species. To confirm this speculation, the fads2 candidate promoter (2646 bp) was cloned from carnivorous marine teleost Epinephelus coioides, and 330 bp core regulatory region was identified. Several binding sites for transcriptional factors such as nuclear factor 1, nuclear factor Y, sterol regulatory element and hepatocyte nuclear factor 4γ were identified, while that for Sp1 was shown to be absent in the promoter by both bioinformatic analysis and site-directed mutation. Moreover, after the Sp1-binding site from the fads2 promoter of herbivorous Siganus canaliculatus, the first marine teleost demonstrated to have LC-PUFA biosynthetic ability, was inserted into the corresponding region of E. coioides fads2 promoter, activity was significantly increased. The results provided direct data for the importance of the Sp1-binding site in determining fads2 promoter activity, and indicated that its lack may be a reason for low expression of fads2 and poor LC-PUFA biosynthetic ability in E. coioides.

Functional characterization of fatty acyl desaturase Fads2 and Elovl5 elongase in the Boddart’s goggle-eyed goby,Boleophthalmus boddarti(Gobiidae) suggest an incapacity for long-chain polyunsaturated fatty acid biosynthesis

“…The notable presence of B. boddarti fads2 transcript in brain tissue is similar to findings from many marine and freshwater species (Monroig et al, 2013, Ren et al, 2013, Tanomman et al, 2013, Wang et al, 2014, Kuah et al, 2016, Janaranjani et al, 2018, Xie et al, 2018). Given the importance of DHA in neuronal-rich tissues such as brain and eye, having the endogenous capacity for LC-PUFA biosynthesis is advantageous when supply from dietary intake is insufficient.…”

“…A possible reason for low desaturation activities in Fads2 could be due to inferior expression at the mRNA level. Elsewhere, work on the promoter region of species with low Fads2 activities showed the absence of critical binding site which are crucial for basal expression in species with notable expression levels (Zheng et al, 2009b, Xie et al, 2018).…”

Stearoyl-CoA desaturase (scd1a) is epigenetically regulated by broodstock nutrition in gilthead sea bream (Sparus aurata)

“…This risk assessment is especially relevant in marine farmed fish, since they have a limited ability to convert α-linolenic acid (ALA, 18:3n-3) into eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) [17]. Fatty acid desaturase 2 (Fads2) catalyzes the first and rate limiting step in this pathway and its regulation and activity has been studied in a wide-range of marine (gilthead sea bream [18], black sea bream [19], European sea bass [20], Japanese sea bass [21], large yellow croaker [22], orange-spotted grouper [23]) and freshwater (rainbow trout [22], striped snakehead [24]) fish species. A main outcome is that diets with low levels of n-3 long chain polyunsaturated fatty acids (n-3 LC-PUFA) up-regulate the expression of fads2, but with differences among fish species that highly reflect the basal activity of their promoters and their differences in LC-PUFA biosynthetic abilities [22,23,25].…”

“…Fatty acid desaturase 2 (Fads2) catalyzes the first and rate limiting step in this pathway and its regulation and activity has been studied in a wide-range of marine (gilthead sea bream [18], black sea bream [19], European sea bass [20], Japanese sea bass [21], large yellow croaker [22], orange-spotted grouper [23]) and freshwater (rainbow trout [22], striped snakehead [24]) fish species. A main outcome is that diets with low levels of n-3 long chain polyunsaturated fatty acids (n-3 LC-PUFA) up-regulate the expression of fads2, but with differences among fish species that highly reflect the basal activity of their promoters and their differences in LC-PUFA biosynthetic abilities [22,23,25]. Conversely, low n-3 C-PUFA diets lead to increased liver fat deposition in freshwater, salmonids and typically marine farmed fish [26][27][28][29], being liver steatosis a common sign of deficiencies in essential fatty acids [30].…”

Sterol regulatory element binding protein and Sp1 is required for transcriptional activation of a freshwater carnivorous fish (Channa striata) elovl5 elongase

“…These G-rich sequences are ubiquitous regulatory elements in many genes and have been shown to cooperate with Srebp in regulation of lipid metabolism (Reed et al, 2008). Sp1 binding sites was found in fads2 promoter of several teleost species with significant Fads2 activities, such as zebrafish, salmon and rabbit fish but missing in several marine carnivorous counterparts, leading to the speculation of Sp1 having an integral role for fads2 expression (Zheng et al, 2009, Geay et al, 2012, Xie et al, 2018. We now showed the presence of several putative Sp-1 binding sites in the promoter of a freshwater carnivorous teleost elovl5 with validation of their requirements for basal transcription.…”