Leptin has been widely known for its potential help in public health, especially in obesity, as its pivotal role in regulating energy homeostasis and reproductive functions in mammals. While, here, you might would be fascinated by Dr. YU Li and his colleagues’ story about the novel interesting characteristics of leptin and Leptin receptor gene (LPR).
Marine mammals are remarkable and evolutionarily significant in terms of their adaptation to an aquatic environment, yet there have been few studies of the genetic changes underlying adaptation to an aquatic lifestyle. In Dr. Yu’s research, the identification of novel leptin genes in 4 species of Cetacea have been reported by comparing with the 55 publicly available leptin sequences from mammalian genome assemblies. The evidence for positive selection in the suborder Odontoceti (toothed whales) of the Cetacea and the family Phocidae (earless seals) of the Pinnipedia, and the positive selection in several leptin gene residues in these two lineages have been presented. Whereas, no signs of positive selection were detected in suborder Mysticeti of Cetacea and family Otariidae of Pinnipedia.
Leptin in marine mammals has failed to indicate body fat deposit and energy reserve balancing and it is expressed in a variety of tissues and blood fluids besides adipose tissues, including placenta, stomach, bone marrow and mammary epithelium. Leptin is not only involved in growth regulation, gastric function, brain development, hematopoiesis, and inflammation, but also adaptively under evolution in deep-diving Phocidae, but not in shallow-diving Otariidae. So, based on these facts, the conclusion about the positive selection in the leptin genes of both Cetacea and Pinnipedia and diversity of its relevant physiological roles has been well defended.
But, no clue which indicates the co-evolution of leptin and its receptor has been detected across the Cetacea and Pinnipedia lineages by analyzing 24 LPR sequences from available mammalian genome assemblies and other published data. Moreover, the positively selected sites identified in the leptin genes of these two lineages were located outside of leptin receptor binding sites. This discrepancy was explained by assuming that the novel leptin functions other than energy balance in Cetacea and Pinnipedia may be independent of the physical interaction between leptin and its receptor. And this unique evolutionary pattern of leptin may have resulted from the multi-functionality of leptin and leptin receptor, supporting the view that the biological roles of leptin vary from species to species.
In summary, this research shed lights 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.
More details about the article and authors please see: PLoS ONE 6(10): e26579. doi:10.1371/journal.pone.0026579
