Department of Biology, University of Bergen, N-5020 Bergen, Norway.
Gen Comp Endocrinol. 2010 Aug 1;168(1):55-70. doi: 10.1016/j.ygcen.2010.04.010. Epub 2010 Apr 18.
The present study reports the complete coding sequences for two paralogues for leptin (sLepA1 and sLepA2) and leptin receptor (sLepR) in Atlantic salmon. The deduced 171-amino acid (aa) sequence of sLepA1 and 175 aa sequence for sLepA2 shows 71.6% identity to each other and clusters phylogenetically with teleost Lep type A, with 22.4% and 24.1% identity to human Lep. Both sLep proteins are predicted to consist of four helixes showing strong conservation of tertiary structure with other vertebrates. The highest mRNA levels for sLepA1 in fed fish (satiation ration=100%) were observed in the brain, white muscle, liver, and ovaries. In most tissues sLepA2 generally had a lower expression than sLepA1 except for the gastrointestinal tract (stomach and mid-gut) and kidney. Only one leptin receptor ortholog was identified and it shares 24.2% aa sequence similarity with human LepR, with stretches of highest sequence similarity corresponding to domains considered important for LepR signaling. The sLepR was abundantly expressed in the ovary, and was also high in the brain, pituitary, eye, gill, skin, visceral adipose tissue, belly flap, red muscle, kidney, and testis. Fish reared on a rationed feeding regime (60% of satiation) for 10 months grew less than control (100%) and tended to have a lower sLepA1 mRNA expression in the fat-depositing tissues visceral adipose tissue (p<0.05) and white muscle (n.s.). sLepA2 mRNA levels was very low in these tissues and feeding regime tended to affect its expression in an opposite manner. Expression in liver differed from that of the other tissues with a higher sLepA2 mRNA in the feed-rationed group (p<0.01). Plasma levels of sLep did not differ between fish fed restricted and full feeding regimes. No difference in brain sLepR mRNA levels was observed between fish fed reduced and full feeding regimes. This study in part supports that sLepA1 is involved in signaling the energy status in fat-depositing tissues in line with the mammalian model, whereas sLepA2 may possibly play important roles in the digestive tract and liver. At present, data on Lep in teleosts are too scarce to allow generalization about how the Lep system is influenced by tissue-specific energy status and, in turn, may regulate functions related to feed intake, growth, and adiposity in fish. In tetraploid species like Atlantic salmon, different Lep paralogues seems to serve different physiological roles.
本研究报告了两种瘦素（sLepA1 和 sLepA2）和瘦素受体（sLepR）在大西洋鲑鱼中的完整编码序列。sLepA1 的 171 个氨基酸（aa）序列和 sLepA2 的 175 aa 序列彼此之间具有 71.6%的同源性，并与鱼类的 Lep 型 A 聚类，与人类的 Lep 具有 22.4%和 24.1%的同源性。这两种 sLep 蛋白都预测由四个螺旋组成，与其他脊椎动物的三级结构具有很强的保守性。在喂食的鱼中（饱食水平=100%），sLepA1 的 mRNA 水平在大脑、白肌、肝脏和卵巢中最高。在大多数组织中，sLepA2 的表达一般低于 sLepA1，除了胃肠道（胃和中肠）和肾脏。仅鉴定出一个瘦素受体直系同源物，它与人类 LepR 的 aa 序列相似性为 24.2%，与被认为对 LepR 信号传导重要的区域相对应的区域具有最高的序列相似性。sLepR 在卵巢中大量表达，在大脑、垂体、眼睛、鳃、皮肤、内脏脂肪组织、腹部皮瓣、红肌、肾脏和睾丸中也高度表达。在限制喂养（饱食的 60%）10 个月的鱼类生长速度低于对照组（100%），并且在脂肪沉积组织内脏脂肪组织（p<0.05）和白肌（n.s.）中的 sLepA1 mRNA 表达倾向较低。这些组织中的 sLepA2 mRNA 水平非常低，并且喂养方式倾向于以相反的方式影响其表达。肝脏中的表达与其他组织不同，在限制喂养组中 sLepA2 mRNA 水平更高（p<0.01）。限制和完全喂养组之间的鱼类血浆 sLep 水平没有差异。在限制和完全喂养组之间，鱼脑中的 sLepR mRNA 水平没有差异。本研究部分支持 sLepA1 参与信号传递脂肪沉积组织中的能量状态，与哺乳动物模型一致，而 sLepA2 可能在消化道和肝脏中发挥重要作用。目前，有关鱼类 Lep 的数据太少，无法概括 Lep 系统如何受组织特异性能量状态的影响，反过来又可能调节与摄食、生长和肥胖相关的功能。在像大西洋鲑鱼这样的四倍体物种中，不同的 Lep 旁系同源似乎具有不同的生理作用。
