Gene structures of the alpha subunits of human IL-3 and granulocyte-macrophage colony-stimulating factor receptors: comparison with the cytokine receptor superfamily.

Abstract

Recently, many genes encoding the members of the cytokine receptor superfamily (CRSF), which have common structural features, have been characterized. Analyses on the structures of the genes encoding the alpha subunits of human IL-3 (hIL-3R alpha) and granulocyte-macrophage colony-stimulating factor receptors (hGMR alpha) revealed that they have the structural features common to all members of the CRSF (i.e., conservation of the intron phase pattern as "1-2-1-0-1" rule in the fibronectin type III domains located in extracellular segments of type I cytokine receptor subunits. This finding led us to propose a possible model for gene evolution for the CRSF. We pointed out that the CRSF genes derived from a putative common ancestral gene. In addition to these common features, we found an additional intron that is unique to the IL-3R alpha and the GMR alpha genes. This additional intron suggests that the IL-3R alpha and the GMR alpha genes evolved closely in the evolution process of the CRSF genes. This evidence and results of recent studies on the evolution of mammalian X chromosome make it tempting to speculate that a putative common ancestral gene of the subfamily including IL-3R alpha, GMR alpha, and IL-5R alpha emerged in an autosome at least before the divergence of marsupials and eutherian mammals, early in the 200 million-year history of mammals.