Abstract
Previous studies on the immunoglobulin (Ig) genes in avian species are limited (mainly to galliformes and anseriformes) but have revealed several interesting features, including the absence of the IgD and Igκ encoding genes, inversion of the IgA encoding gene and the use of gene conversion as the primary mechanism to generate an antibody repertoire. To better understand the Ig genes and their evolutionary development in birds, we analyzed the Ig genes in the ostrich (Struthio camelus), which is one of the most primitive birds. Similar to the chicken and duck, the ostrich expressed only three IgH chain isotypes (IgM, IgA and IgY) and λ light chains. The IgM and IgY constant domains are similar to their counterparts described in other vertebrates. Although conventional IgM, IgA and IgY cDNAs were identified in the ostrich, we also detected a transcript encoding a short membrane-bound form of IgA (lacking the last two CH exons) that was undetectable at the protein level. No IgD or κ encoding genes were identified. The presence of a single leader peptide in the expressed heavy chain and light chain V regions indicates that gene conversion also plays a major role in the generation of antibody diversity in the ostrich. Because the ostrich is one of the most primitive living aves, this study suggests that the distinct features of the bird Ig genes appeared very early during the divergence of the avian species and are thus shared by most, if not all, avian species.
Highlights
The adaptive immune system of jawed vertebrates is characterized by the production of immunoglobulins (Igs) in response to antigens [1]
Three Ig isotypes (IgM, IgA and IgY, but not IgD nor Igk), were identified in the ostrich, which is a primitive avian species belonging to the order struthioniformes
Southern blotting indicated that there was more than one copy of the m and u genes in the ostrich genome, we were only able to obtain one copy of the m and u expressed at the cDNA level
Summary
The adaptive immune system of jawed vertebrates is characterized by the production of immunoglobulins (Igs) in response to antigens [1]. Compared with IgM, IgD shows a high degree of structural plasticity because of variance in the copy number and number of CH encoding exons as well as alternative RNA splicing [13]. In addition to these ancient Ig classes, some additional distinct Ig classes have been found in different vertebrates, such as IgY in lower tetrapods [7,9,14], IgNAR in cartilaginous fish [15], IgT/IgZ in the trout and zebrafish [16,17], IgX and IgF in amphibians [6,18], and IgO in the platypus [19]
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have