瘦蛋白基因(leptin)在哺乳动物的能量平衡和生殖调控等方面有重要作用。以前对该基因的研究主要集中于它对人类健康，尤其是肥胖症方面。而对该基因所具有的其它可能的新功能却知之甚少。
中国科学院昆明动物研究所张亚平院士课题组和云南大学于黎研究员，博士研究生靳伟等测定了海洋哺乳动物--鲸目代表物种的leptin基因，并结合55条网上已有哺乳动物leptin序列进行研究。研究结果发现在鲸目中的齿鲸亚目祖先枝和食肉目水生鳍脚类中的海豹科祖先枝都发现了正选择作用和正选择位点。而鲸目中的须鲸亚目祖先枝和食肉目中水生鳍脚类中的海狮科祖先枝都没有发现正选择作用。提示leptin基因在海洋哺乳动物的特定类群中，包括须鲸亚目和海豹科物种中产生了新的组织特异性和新功能，如与深水潜水有关的呼吸系统功能适应。此外，我们还对与瘦蛋白结合的瘦蛋白受体（leptin receptor）基因进行了分析，研究结果并没有在鲸目和食肉目鳍脚类中发现正选择。因此leptin和leptin receptor基因之间不存在共进化。本研究为哺乳动物从陆地到海洋转变过程中的leptin进化和可能具有的新功能提供了重要信息。
研究结果已发表在国际刊物《PLOS ONE》上(Yu et al. 2011. 6: e26579)。（生物谷 Bioon.com）
doi:10.1371/journal.pone.0026579
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Evidence for Positive Selection on the Leptin Gene in Cetacea and Pinnipedia
Li Yu, Wei Jin, Xin Zhang, Ding Wang, Jin-song Zheng, Guang Yang, Shi-xia Xu, Soochin Cho, Ya-ping Zhang
The leptin gene has received intensive attention and scientific investigation for its importance in energy homeostasis and reproductive regulation in mammals. Furthermore, study of the leptin gene is of crucial importance for public health, particularly for its role in obesity, as well as for other numerous physiological roles that it plays in mammals. In the present work, we report the identification of novel leptin genes in 4 species of Cetacea, and a comparison with 55 publicly available leptin sequences from mammalian genome assemblies and previous studies. Our study provides evidence for positive selection in the suborder Odontoceti (toothed whales) of the Cetacea and the family Phocidae (earless seals) of the Pinnipedia. We also detected positive selection in several leptin gene residues in these two lineages. To test whether leptin and its receptor evolved in a coordinated manner, we analyzed 24 leptin receptor gene (LPR) sequences from available mammalian genome assemblies and other published data. Unlike the case of leptin, our analyses did not find evidence of positive selection for LPR across the Cetacea and Pinnipedia lineages. In line with this, positively selected sites identified in the leptin genes of these two lineages were located outside of leptin receptor binding sites, which at least partially explains why co-evolution of leptin and its receptor was not observed in the present study. Our study provides interesting insights into current understanding of the evolution of mammalian leptin genes in response to selective pressures from life in an aquatic environment, and leads to a hypothesis that new tissue specificity or novel physiologic functions of leptin genes may have arisen in both odontocetes and phocids. Additional data from other species encompassing varying life histories and functional tests of the adaptive role of the amino acid changes identified in this study will help determine the factors that promote the adaptive evolution of the leptin genes in marine mammals.
