High-resolution mapping of the human 4q21 and the mouse 5E3 SCYB chemokinecluster by fiber-fluorescence in situ hybridization

The CXC chemokine or small inducible cytokine B (SCYB) subfamily includes t he T-cell chemoattractants MIG (CXCL9, SCYB9), IP-10 (CXCL10, SCYB10), and I-TAC (CXCL11, SCYB11). These three highly homologous chemokines lack the g lutamic acid-leucine-arginine (ELR) motif and signal via the CXCR3 receptor . Previous work showed that the genes encoding these chemokines are localiz ed in an individual mini-cluster on human Chromosome (Chr) 4 at position 4q 21.2. Recently, we identified mouse Scyb11 and mapped this gene by fluoresc ence in situ hybridization (FISH) to mouse Chr 5E3, the orthologous locus t o human 4q21 where the other two homologous mouse genes, Seyb9 and Scyb10, have also been localized. Since SCYB10 and SCYB11 are not represented in th e recently published draft sequence of the human genome, we wanted to clari fy exactly the order and distances of the three chemokine genes using, two- color FISH on stretched DNA fiber preparations. Here, we report the simulta neous localization of all three genes and provide high-resolution visual ma ps of this chemokine cluster C from both mouse and human. The three chemoki ne genes were found within a range of 32 kb on mouse and 29 kb on human DNA fiber targets. The precise physical distances were defined, and an almost identical arrangement of the human and mouse homologues was identified, ind icating that this CXC chemokine mini-cluster has been completely conserved evolutionarily since the divergence of mouse and human. Our results refine previous maps of the three genes, support the hypothesis that they resulted from gene duplication that took place in a common ancestor of mouse and hu man, and provide complementary information on region of the draft sequence of human Chr 4 that is not yet covered.