Research Paper Volume 12, Issue 4 pp 3516—3557
Adaptive selection in the evolution of programmed cell death-1 and its ligands in vertebrates
- 1 Guangdong Key Laboratory of Animal Conservation and Resource Utilization, Guangdong Public Laboratory of Wild Animal Conservation and Utilization, Guangdong Institute of Applied Biological Resources, Guangzhou, Guangdong, China
- 2 College of Animal Science and Technology, Huazhong Agricultural University, Wuhan, China
- 3 Department of Zoology, The Islamia University, Bahawalpur, Pakistan
- 4 Animal Production Department, Faculty of Agriculture, Benha University, Moshtohor, Egypt
- 5 Department of Animal Breeding and Genetics, Cholistan University of Veterinary and Animal Sciences, Bahawalpur, Pakistan
received: December 4, 2019 ; accepted: January 28, 2020 ; published: February 11, 2020 ;https://doi.org/10.18632/aging.102827
How to Cite
Copyright © 2020 Ahmad et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY 3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Programmed cell death-1 (PD-1) and its ligands, particularly PD-L1 and PD-L2, are the most important proteins responsible for signaling T-cell inhibition and arbitrating immune homeostasis and tolerance mechanisms. However, the adaptive evolution of these genes is poorly understood. In this study, we aligned protein-coding genes from vertebrate species to evaluate positive selection constraints and evolution in the PD1, PD-L1 and PD-L2 genes conserved across up to 166 vertebrate species, with an average of 55 species per gene. We determined that although the positive selection was obvious, an average of 5.3% of codons underwent positive selection in the three genes across vertebrate lineages, and increased positive selection pressure was detected in both the Ig-like domains and transmembrane domains of the proteins. Moreover, the PD1, PD-L1 and PD-L2 genes were highly expressed in almost all tissues of the selected species indicating a distinct expression pattern in different tissues among most species. Our study reveals that adaptive selection plays a key role in the evolution of PD1 and its ligands in the majority of vertebrate species, which is in agreement with the contribution of these residues to the mechanisms of pathogen identification and coevolution in the complexity and novelties of vertebrate immune systems.