Immunoglobulin heavy chains in medaka (Oryzias latipes)
1 Oceanographic Center of Vigo, Spanish Institute of Oceanography (IEO), Subida a Radio Faro 50, 36390 Vigo, Pontevedra, Spain
2 Shared Unit of Immunology, University of Vigo - Vigo University Hospital Complex (Hospital Meixoeiro), Edificio de Ciencias Experimentales, Rua das Abeleiras, Campus As LagoasMarcosende, Vigo 36310, Pontevedra, Spain
3 Unidad de Inmunología, Hospital do Meixoeiro, Servizo Galego de Saude (SERGAS), Carretera de Madrid s/n, Vigo 36210, Pontevedra, Spain
BMC Evolutionary Biology 2011, 11:165 doi:10.1186/1471-2148-11-165Published: 15 June 2011
Bony fish present an immunological system, which evolved independently from those of animals that migrated to land 400 million years ago. The publication of whole genome sequences and the availability of several cDNA libraries for medaka (Oryzias latipes) permitted us to perform a thorough analysis of immunoglobulin heavy chains present in this teleost.
We identified IgM and IgD coding ESTs, mainly in spleen, kidney and gills using published cDNA libraries but we did not find any sequence that coded for IgT or other heavy chain isotypes described in fish. The IgM - ESTs corresponded with the secreted and membrane forms and surprisingly, the latter form only presented two constant heavy chain domains. This is the first time that this short form of membrane IgM is described in a teleost. It is different from that identified in Notothenioid teleost because it does not present the typical splicing pattern of membrane IgM. The identified IgD-ESTs only present membrane transcripts, with Cμ1 and five Cδ exons. Furthermore, there are ESTs with sequences that do not have any VH which disrupt open reading frames.
A scan of the medaka genome using transcripts and genomic short reads resulted in five zones within a region on chromosome 8 with Cμ and Cδ exons. Some of these exons do not form part of antibodies and were at times interspersed, suggesting a recombination process between zones. An analysis of the ESTs confirmed that no antibodies are expressed from zone 3.
Our results suggest that the IGH locus duplication is very common among teleosts, wherein the existence of a recombination process explains the sequence homology between them.