Molecular organization of the cytokine gene cluster, involving the human IL-3, IL-4, IL-5, and GM-CSF genes, on human chromosome 5

The human genes for the hematopoietic growth factors interleukin-3 (IL- 3), IL-5, and granulocyte-macrophage colony-stimulating factor (GM-CSF) have been mapped to 5q23–31. We present in situ hybridization evidence that the human IL-4 gene is located at 5q23.3–31.2, suggesting that the four cytokine genes may be closely linked. We used pulsed-field gel electrophoresis to prepare subchromosomal restriction maps surrounding these genes to define this possible linkage more precisely. The IL-4 and IL-5 genes are tightly linked, being 90 to 240 kilobases (kb) apart, as has been shown for the IL-3 and GM-CSF genes, which are only 9 kb apart. Possible overlap of the map containing the IL-4 and IL-5 genes with restriction sites 5′ to the IL-3 gene suggests that the four cytokine genes may be localized within 500 kb of each other. The endothelial cell growth factor gene (ECGF), which has also been localized to the 5q31 region, did not appear to be close to the cytokine genes. Linkage of the IL-3, IL-4, IL-5, and GM-CSF genes has important implications in the evolutionary origin and regulation of expression of these genes. The four cytokine genes are located in the region of the long arm of chromosome 5, which is deleted in the 5q- anomaly. The present study provides a basis for further investigations of this disorder.