Immunogenetics

, Volume 49, Issue 4, pp 362–367

Evolution of the Mhc class I region: the framework hypothesis

  • Claire Amadou
HYPOTHESIS

DOI: 10.1007/s002510050507

Cite this article as:
Amadou, C. Immunogenetics (1999) 49: 362. doi:10.1007/s002510050507

Abstract

 A comparison of the major histocompatibility complex (Mhc) region between human and mouse highlights both stability and differences. The class II and class III regions are orthologous; they probably existed in the ancestor in a similar organization and were not subjected to major rearrangement. The class I genes, by contrast, are definitely paralogous, having been reorganized several times. As long as only class I genes were identified, the class I regions of human and mouse were difficult to compare directly. The identification of non-class I genes has allowed a comparative map to be drawn, which shows that the class I region is orthologous between human and mouse as well. The lack of orthology specifically applies to the class I sequences. However, the comparative map shows that the non-orthologous class I sequences occupy homologous locations with regard to the conserved genes. I propose a model to explain this paradox. The conserved genes may represent samples of a dense "framework" of genes whose alterations are deleterious. The homologous positions occupied by class I genes would thus represent the few permissive places allowing major perturbations. The evolution of the class I sequences, by duplication and deletion, independently in the two species, has taken place within the scope defined by the framework: insertion at the permissive places, and expansion by creation of class I-related DNA by duplication, thus pushing back the boundaries of the framework.

Key words Major histocompatibility complex Class I region Evolution Orthology Olfactory receptor genes 

Copyright information

© Springer-Verlag Berlin Heidelberg 1999

Authors and Affiliations

  • Claire Amadou
    • 1
  1. 1.Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75235–9050, USA, E-mail: amadou@utsw.swmed.edu, Tel: +1-214-6485074, Fax: +1-214-6485453US