Linked Life Data

8454860

Source:http://linkedlifedata.com/resource/pubmed/id/8454860

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
7
pubmed:dateCreated
1993-4-20
pubmed:databankReference
pubmed:abstractText
The amphibian Xenopus laevis is the most primitive vertebrate in which the MHC has been identified both at the biochemical and functional levels. In the present study, cDNA clones for MHC class II beta-chain genes of X. laevis were isolated using the polymerase chain reaction. In partially inbred animals with the MHC f haplotype, two distinct cDNA clones assumed to encode isotypes were identified. The deduced MHC class II beta-chains of X. laevis had structures fundamentally similar to those of their mammalian counterparts. The overall amino acid sequence identity between X. laevis and representative mammalian MHC class II beta-chains was approximately 41 to 50%. Sequence comparison of cDNA clones isolated from outbred subjects and the partially inbred frog with the MHC f haplotype showed that nucleotide substitutions are located primarily in the beta 1 domain and that non-synonymous substitutions occur more frequently than synonymous substitutions in the putative Ag-binding sites. This result indicates that, as in mammalian MHC genes, the MHC class II beta-chain genes of X. laevis are under positive Darwinian selection. Despite the fact that X. laevis is a tetraploid species, its MHC, as defined by serology, immunochemistry, and MLR, is diploidized. Family studies showed that all MHC class II beta-chain genes detectable in the genome of X. laevis segregate with serologically defined MHC haplotypes, suggesting that the second, inactivated set of MHC class II beta-chain genes was either deleted or that their sequences diverged too far to be detected by DNA hybridization. Furthermore, a nearly constant number of MHC class II beta-chain genes was detectable in most, if not all, Xenopus species with various degrees of ploidy. Thus, various polyploid species of Xenopus appear to have used a similar strategy to diploidize their MHC genes.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
AIM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Apr
pubmed:issn
0022-1767
pubmed:author
pubmed:issnType
Print
pubmed:day
1
pubmed:volume
150
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
2831-43
pubmed:dateRevised
2009-11-19
pubmed:meshHeading
pubmed:year
1993
pubmed:articleTitle
Evolution of the MHC: isolation of class II beta-chain cDNA clones from the amphibian Xenopus laevis.
pubmed:affiliation
Department of Microbiology and Immunology, University of Miami School of Medicine, FL 33101.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S., Research Support, Non-U.S. Gov't