Central and peripheral clocks in Atlantic bluefin tuna (Thunnus thynnus, L.): Daily rhythmicity of hepatic lipid metabolism and digestive genes

Abstract

Atlantic bluefin tuna (ABT; Thunnus thynnus) is a highly regarded and consumed species, but farming is still in its infancy. Currently, nothing is known about the presence of circadian rhythmicity at central or peripheral tissues, or if there are daily rhythms in expression of genes involved in lipid metabolism. In order to elucidate clock gene regulation of genes of lipid metabolism in ABT, six clock genes (bmal1, clock, cry1, cry2, per1 and per2) were sequenced and 24 h expression of these genes determined in brain and liver of fish acclimated to a light:dark (L:D) photoperiod. Additionally, the daily expression of lipid metabolism and digestive enzyme genes in ABT was also determined in liver. All six clock genes displayed rhythmicity in the brain and liver, other than cry2, which did not show an acrophase in liver. In liver, all the transcription factors analysed other than srebp1 and srebp2 displayed rhythmicity, with lxr and pparα displaying diurnal expression, whereas pparγ was highly expressed at the end of the scotophase. Some of the target genes of lxr such as elovl5 and lpl also oscillated rhythmically, with acrophases during the photophase. In contrast, only three of the eight digestive enzyme genes studied displayed rhythmicity, at different times of the day, suggesting that either ABT display different feeding periods or the digestion of some nutrients (e.g. lipids) is prioritized over others. The present study showed that clock and lipid metabolism genes displayed strong daily rhythmicity in ABT brain and liver, which could be an area of considerable interest for the establishment of efficient feeding protocols in this new aquaculture species.

Rhythmic expressions of biological clocks and metabolic genes in marine medaka ( Oryzias melastigma )

“…Pparα reaches the top at the beginning and mid of the photoperiod, which was similar in mice, Atlantic salmon and Atlantic bluefin tuna (Betancor et al, 2014(Betancor et al, , 2020Yang et al, 2006), and Pparγ reaches the top at the middle and late photoperiod. The Srebp1 transcription factor also reached its peak at the beginning and mid of the photoperiod, and its target genes Fadsd2 and Elovl5 showed obvious daily rhythm in treatment 2#.…”

“…For example, Bmal1 expressed its peak at the beginning of light period under L:D=16:8, and the phenomenon was also observed in the brain of rainbow trout and zebrafish during the dark and light transitions (Ló et al, 2011;Whitmore et al, 1998). But, there were other reports that observed the expression of Bmal1 reached its maximum at the late light period in other bony fish (Betancor et al, 2020;Vera et al, 2013). These results illustrated that the expression of Bmal1 would be different in different species.…”

“…Fadsd2 is a key enzyme in the biosynthesis pathway of unsaturated fatty acids. In Atlantic bluefin tuna, except for Fadsd2, Elov15 and Lpl also had similar rhythmic expression (Betancor et al, 2020). Among the four protein and carbohydrate metabolism genes tested, two genes (Tryp, Pck) showed obvious rhythmic expression, all of which indicated that some metabolic pathways were closely related to the clock system.…”

Effects of LED spectrum on circadian rhythmic expression of clock genes and Aanat2 in the brain of juvenile European seabass (Dicentrarchus labrax)

“…Currently in fish, the biological clock genes were mainly studied in some model species, such as zebrafish (Danio rerio) (Whitmore et al, 1998), Takifugu rubripes (Delaunay et al, 2000), Oryzias latipes (Cuesta et al, 2014), etc. There are a small number of cultured species, such as the European cockroach (Dicentrarchus labrax), rainbow trout (Oncorhynchus mykiss), Atlantic salmon (Salmo salar), Atlantic cockroach (Gadus morhua), Atlantic bluefin tuna (Thunnus thynnus, L.) and other biological clock related research (Huang et al, 2010;Sańchez et al, 2010;Patiño et al, 2011;Nagasawa et al, 2012;Lazado et al, 2014;Betancor et al, 2020).…”

De novo transcriptome assembly, functional annotation and characterization of the Atlantic bluefin tuna (Thunnus thynnus) larval stage

“…Recently, more attempts to manipulate the life cycle (i.e. induce spawning) and grow the larvae were carried out with promising achievements (Mylonas et al 2007;De Metrio et al 2010;Reglero et al 2014;Yúfera et al 2014;Blanco et al 2017;Betancor et al 2017;Betancor et al 2019;Betancor et al 2020). In this context, understanding nutritional requirements, growth pattern, responses to external stimuli, morphological and physiological changes and discovering stage-specific markers during the larval development are central points (Gisbert et al 2008;Rønnestad et al 2013).…”