Molecular Evolutionary Study Of G-type Lysozymes In Mammals

Lysozyme plays a role in innate immunity by catalyzing the hydrolysis of ?1-4 glycosidic bonds between N-acetylmuramic acid(NAM)and N-acetylglucosamine(NAG)in peptidoglycan in the bacterial cell wall.Goose(g)-type lysozyme was originally found in goose egg whites,but has since been widely identified in a variety of vertebrates and invertebrates.The g-type lysozyme has been widely studied in fish.Bacteria,viruses and parasites can increase the expression in tissues,and at the same time,it can degrade Gram-positive bacteria and Gram-negative bacteria.At present,the functional studies of mammals are limited to human studies.Two g-type lysozymes have shown different expression patterns: Lyg1 is widely expressed in different human organs,but the highest expression is in the kidney;HIPED database shows Lyg2 is highly expressed in hair follicles / skin,but studies have shown that Lyg2 is highly expressed in human eyes and testes and is present in tears.Multiple gene repeat events of Lyg occurred in different lineages of vertebrates.In mammals,two g-type lysozyme genes(Lyg1 and Lyg2)were generated through early replication.Earlier studies showed that only Lyg2 was found in the genome of cetaceans(alpacas,camels,cattle,sheep,pigs,killer whales,dolphins).However,the number of species involved in the study is limited,and the method of identifying Lyg relies on genomic prediction information,so it is unclear the complete evolution of Lyg1 and Lyg2 in mammals.Here,we obtained Lyg1 and Lyg2 sequences from the 237 mammalian genomes and discovered the gene loss that occurs in different groups of the two.The loss of the Lyg1 gene is mainly concentrated in cetaceans,although some species in the artiodactyla still have complete coding regions.While the loss of Lyg2 is widespread in cetaceans and bats,species in the family Batidae still have complete coding regions.In this regard,we performed Lyg2 PCR amplification and sequencing verification on representative species in cetaceans and bats,and the results showed that the results were consistent with the results obtained by the genome.Interestingly,cetaceans,Florida manatees(Trichechus manatus),Philippine tarsiers(Carlito syrichta),kangaroos(Macropus eugenii),and two bats(Eonycteris spelaea and Pteronotus parnellii)lost both g-type lysozyme genes.But with the exception of cetaceans and Florida manatees,the genome coverage of the other four species is not very high,so sequencing errors cannot be completely ruled out.In addition,the results of selective pressure analysis show that both g-type lysozymes are more conserved than c-type lysozyme,especially the Lyg2 gene,so taking into account the recently reported parallel loss of some genes in cetaceans and manatees,and the high level of Lyg2 in hair follicle / skin Expression and rapid skin regeneration,we speculate that loss of g-type lysozyme in cetaceans and manatees may be related to their complete aquatic lifestyle.