In an achievement that could improve the ability to match tissues for transplantation, scientists have mapped the first complete DNA sequences of the major histocompatibility complex (MHC) of genes from humans and chickens.
The findings "signal a landmark in genome sequencing and will help to reveal the basis of associations between the MHC and susceptibility to diseases such as rheumatoid arthritis and diabetes," said a statement from Nature, which published two letters on DNA sequencing on October 28.
In one letter (1999;401:921-923), investigators in the United States, Japan, England, and France representing the MHC Sequencing Consortium said they had mapped the first complete sequence and gene map of an HMC complex in humans. "Although many of the 224 identified gene loci ... are still of unknown function, we estimate that about 40% of the expressed genes have immune system function," they said. Having a complete sequence "provides an important new tool for studying the genetics, biology, and evolution of human multigene families, populations, and diseases."
In the other letter (1999;401:923-925), investigators from England, Germany, and France reported they sequenced the MHC in chickens. Almost all of the genes have counterparts to the human MHC, but the complex in chickens is about 20 times smaller than the human MHC, which "makes it possible to study the striking MHC-determined pathogen-specific disease resistance at the molecular level," the authors said.
In an accompanying commentary (1999;401:870-871), Peter Parham wrote that the two reports "vividly illustrate that working MHCs come in all shapes and sizes." After 30 years of study by many scientists, he said, the MHC Sequencing Consortium provides "the real thing: a complete nucleotide sequence of an HLA complex and a linear map ordering all of the genes."
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