Discovery and Characterization of the First Genuine Avian Leptin Gene in the Rock Dove (Columba livia)
Discovery and Characterization of the First Genuine Avian Leptin Gene in the Rock Dove (Columba livia)
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DOI：
10.1210/en.2014-1273
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发表时间：
2014-09-01
期刊：
影响因子：
4.8
通讯作者：
Seroussi, Eyal
中科院分区：
文献类型：
--
作者：
Friedman-Einat, Miriam;Cogburn, Larry A.;Seroussi, Eyal
瘦素是哺乳动物能量平衡的关键调节因子，自鸡的瘦素基因（LEP）首次被报道以来，近15年来一直是禽类生物学研究的热点。在这里，我们描述了一种新的LEP在岩鸽（鸽）与预测的蛋白质序列（30%的同一性，47%的相似性）的人类直系同源物的低相似性。搜索Sequence-Read-Archive数据库发现鸽子肝脏中的瘦素转录本，在2个编码外显子之前有2个非编码外显子。这种不寻常的4-外显子结构通过RT-PCR从肝脏RNA扩增的富含GC的产物（76%GC，721 bp）的测序进行验证。鸽子瘦素与orthopleptin的序列比对表明，它由一个前导肽（21个氨基酸; aa），其次是成熟蛋白（160 aa），它具有一个推定的结构典型的4-螺旋束细胞因子，除了它是12个氨基酸比人瘦素。额外的残基（10个氨基酸）位于25 '-螺旋之间的环内，中断了四足动物中保守的氨基酸基序，该基序被认为是激活瘦素受体（LEPR）而不是受体结合本身所必需的。定量RT-PCR结果显示LEP在鸽子肝脏中表达最高（P <0.05），而鸽子LEPR在垂体中表达最高（P <0.01）。这两种基因在性腺中显著表达，在哺乳动物瘦素信号传导相关的组织（脂肪、下丘脑）中表达水平较低。基于鸡LEPR体外激活的生物测定显示鸽子循环中的瘦素活性，表明鸽子LEP编码活性蛋白，尽管中断的环基序。提供工具来研究能量平衡控制在进化的角度来看，我们原来的演示瘦素信号在鸽子预测更古老的作用瘦素在鸟类的生长和繁殖，而不是食欲控制。
Leptin, the key regulator of mammalian energy balance, has been at the center of a great controversy in avian biology for the last 15 years since initial reports of a putative leptin gene (LEP) in chickens. Here, we characterize a novel LEP in rock dove (Columba livia) with low similarity of the predicted protein sequence (30% identity, 47% similarity) to the human ortholog. Searching the Sequence-Read-Archive database revealed leptin transcripts, in the dove's liver, with 2 noncoding exons preceding 2 coding exons. This unusual 4-exon structure was validated by sequencing of a GC-rich product (76% GC, 721 bp) amplified from liver RNA by RT-PCR. Sequence alignment of the dove leptin with orthologous leptins indicated that it consists of a leader peptide (21 amino acids; aa) followed by the mature protein (160 aa), which has a putative structure typical of 4-helical-bundle cytokines except that it is 12 aa longer than human leptin. Extra residues (10 aa) were located within the loop between 25'-helices, interrupting the amino acid motif that is conserved in tetrapods and considered essential for activation of leptin receptor (LEPR) but not for receptor binding per se. Quantitative RT-PCR of 11 tissues showed highest (P < .05) expression of LEP in the dove's liver, whereas the dove LEPR peaked (P < .01) in the pituitary. Both genes were prominently expressed in the gonads and at lower levels in tissues involved in mammalian leptin signaling (adipose; hypothalamus). A bioassay based on activation of the chicken LEPR in vitro showed leptin activity in the dove's circulation, suggesting that dove LEP encodes an active protein, despite the interrupted loop motif. Providing tools to study energy-balance control at an evolutionary perspective, our original demonstration of leptin signaling in dove predicts a more ancient role of leptin in growth and reproduction in birds, rather than appetite control.