High-resolution FISH mapping of the rat alpha2u-globulin multigene family

The rat alpha2u-globulins are a group of similar proteins that are encoded by a family of approximately 20 genes located a single locus of < or =880 kbp on Chromosome (Chr) 5q. Individual members of this gene family demonstrate complex tissue, hormonal, and developmental expression patterns despite a high degree of sequence similarity among the members and consequently provide an interesting system for studying the evolution of differential gene expression. Hybridization analysis indicated that gene classes, similar to those identified at the homologous MUP locus in the mouse, do not exist within the rat alpha2u-globulin locus. Furthermore, cross-hybridization analysis revealed the presence of conserved sequences in the 5' and 3' regions flanking the alpha2u-globulin genes, some of which were present in an inverted orientation. We have used high-resolution fiber FISH to examine the structural organization of the alpha2u-globulin locus, and found the genes to be arranged as an array of both direct and inverted repeats. The organization of the rat alpha2u-globulin genes differs from the MUP genes and suggests different evolutionary events have reorganized these homologous sets of genes.