Study On The Evolution Of Fish Type ? Interferons And Their Receptors

In mammals,Type ? Interferon is a type of glycoprotein produced by the immune cells after being stimulated by interferon inducers.It plays an important role in the resistance to intracellular bacterial infections and viruses.Two type ? interferons,IFN-? and IFN-?rel,have been found by now.IFN-?rel is unique to fish.Fish IFN-? has high homology with lower vertebrate IFN-? and the research on its evolutionary history is relatively complete.However,issues such as the origin of IFN-?rel,its status and divergence during fish evolution,and the cophylogeny relationship with receptors,comparison with the evolutionary history of IFN-? have not been clarified.Therefore,this thesis focused on the above issues to comprehensively explore the evolution of fish type ? interferons and their receptors.Firstly,this study supplemented and improved the genetic information of type ? interferons and their receptors in the bony fish by comprehensive analysis of existing genomic data of fish.For example,IFN-?rel was found in the genome of the Asian arowana(Scleropages formosus),which is the first evidence of the existence of the IFN-?rel gene in the oldest bony fish.Secondly,the maximum likelihood approach and Bayesian inference were used to phylogenetic reconstruction about the representative fish type ? interferons and their receptors.The results showed that the evolutionary history of IFN-?rel is significantly different between the early and late stages of teleostei evolution.Its relationship with IFN-? also changed as the fish evolved.Next,in this study,global-fit method and Event-based meothod were used to analyze the synergistic phylogeny of fish type ? interferon ligands and receptors.The results showed that Ostariophysi is the dividing line,which divides ligands-receptors into two cophylogeny relationships.This work discussed the situation of multiple ligands and multiple receptors in some fishes caused by Whole Genome Duplication(WGD),and detailedly analyzed the cophylogeny relationships between them.A total of 52 times of cospeciation,47 times of host switching event,7 times of duplication,40 times of loss and 8 times of failure to diverge occurred in the cophylogeny of type II fish interferon ligands and receptors.Finally,this study compared the selection pressure of fish IFN-? and IFN-?rel during evolution.The results revealed that they have significantly different positive selection amino acid sites.There are three positive selection sites of IFN-?.Two of them are in the third and fourth ? helices of IFN-? protein,and the one left is in the loop region of both helices.There are six positive selection sites of IFN-?rel,and all of them are in the ? helices.It shows that they have different adaptive evolution processes in water environment.In this thesis,we systemaitcally studied the evolutionary history of fish type ? interferons and their receptors.Therefore,it provides a theoretical basis for improving the function and status of type ? interferons in fish immune system,and deepens our understanding of their structure and function evolution in immune evolution process.Additionally,it reveals the role of immune system in the evolution of the entire vertebrate and also demonstrates the immune adaptation changes caused by water or land environment.