title: Extensive diversification of IgH subclass-encoding genes and IgM subclass switching in crocodilians.
abstract: Crocodilians are a group of reptiles that are closely related to birds and are thought to possess a strong immune system. Here we report that the IgH locus in the Siamese crocodile and the Chinese alligator contains multiple μ genes, in contrast to other tetrapods. Both the μ2 and μ3 genes are expressed through class-switch recombination involving the switch region and germline transcription. Both IgM1 and IgM2 are present in the serum as polymers, which implies that IgM class switching may have significant roles in humoural immunity. The crocodilian α genes are the first IgA-encoding genes identified in reptiles, and these genes show an inverted transcriptional orientation similar to that of birds. The identification of both α and δ genes in crocodilians suggests that the IgH loci of modern living mammals, reptiles and birds share a common ancestral organization.
authors.affiliation: State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, Beijing 100193, China.
authors.forename: Gang
authors.initials: G
authors.lastname: Cheng
authors.forename: Yang
authors.initials: Y
authors.lastname: Gao
authors.forename: Tao
authors.initials: T
authors.lastname: Wang
authors.forename: Yi
authors.initials: Y
authors.lastname: Sun
authors.forename: Zhiguo
authors.initials: Z
authors.lastname: Wei
authors.forename: Lingxiao
authors.initials: L
authors.lastname: Li
authors.forename: Liming
authors.initials: L
authors.lastname: Ren
authors.forename: Ying
authors.initials: Y
authors.lastname: Guo
authors.forename: Xiaoxiang
authors.initials: X
authors.lastname: Hu
authors.forename: Yan
authors.initials: Y
authors.lastname: Lu
authors.forename: Xumin
authors.initials: X
authors.lastname: Wang
authors.forename: Guiming
authors.initials: G
authors.lastname: Liu
authors.forename: Chenglin
authors.initials: C
authors.lastname: Zhang
authors.forename: Jun
authors.initials: J
authors.lastname: Yu
authors.forename: Qiang
authors.initials: Q
authors.lastname: Pan-Hammarström
authors.forename: Lennart
authors.initials: L
authors.lastname: Hammarström
authors.forename: Xiaobing
authors.initials: X
authors.lastname: Wu
authors.forename: Ning
authors.initials: N
authors.lastname: Li
authors.forename: Yaofeng
authors.initials: Y
authors.lastname: Zhao
mesh_terms: D000489:Alligators and Crocodiles / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D005091:Exons / Q000235:genetics; D005784:Gene Amplification / Q000235:genetics; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D015723:Gene Library; D056426:Genetic Loci / Q000235:genetics; D014644:Genetic Variation; D016678:Genome / Q000235:genetics; D005854:Germ Cells / Q000378:metabolism; D017578:Immunoglobulin Class Switching / Q000235:genetics*; D007143:Immunoglobulin Heavy Chains / Q000235:genetics*; D007075:Immunoglobulin M / Q000097:blood / Q000235:genetics*; D007438:Introns / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010802:Phylogeny; D020161:Physical Chromosome Mapping; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011995:Recombination, Genetic / Q000235:genetics; D014158:Transcription, Genetic
chemical_list: D007143:Immunoglobulin Heavy Chains; D007075:Immunoglobulin M; D012333:RNA, Messenger