Analysis of the immunoglobulin light chain genes in zebra finch: evolutionary implications.
All jawed vertebrates produce immunoglobulins (IGs) as a defense mechanism against pathogens. Typically, IGs are composed of two identical heavy chains (IGH) and two identical light chains (IGL). Most tetrapod species encode more than one isotype of light chains. Chicken is the only representative of birds for which genomic information is currently available and is an exception to the above rule because it encodes only a single IGL isotype (i.e., lambda). Here, we show that the genome of zebra finch, another bird species, encodes a single IGL isotype, that is, lambda, like the chicken. These results strongly suggest that the second isotype (i.e., kappa) present in both reptiles and mammals was lost in a very early stage of bird evolution. Furthermore, we show that both chicken and zebra finch contain a single set of functional variable, joining, and constant region genes and multiple variable region pseudogenes. The latter finding suggests that this type of genomic organization was already present in the common ancestor of these bird species and remained unchanged over a long evolutionary time. This conservation is in contrast with the high levels of variation observed in the mammalian IGL loci. The presence of a single functional variable region gene followed by multiple variable pseudogenes in zebra finch suggest that this species may be generating antibody diversity by a gene conversion-like mechanism like the chicken.
Das
Sabyasachi
S
Department of Pathology and Laboratory Medicine, Emory Vaccine Center, School of Medicine, Emory University, USA. sdas8@emory.edu
Mohamedy
Uzra
U
Hirano
Masayuki
M
Nei
Masatoshi
M
Nikolaidis
Nikolas
N
D000595:Amino Acid Sequence; D000818:Animals; D000916:Antibody Diversity; D002645:Chickens; D019143:Evolution, Molecular; D046369:Finches / Q000235:genetics*; D005785:Gene Conversion; D050439:Genes, Immunoglobulin Light Chain / Q000235:genetics*; D005819:Genetic Markers; D008322:Mammals; D008957:Models, Genetic; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016415:Sequence Alignment
D005819:Genetic Markers