Comparative human-mouse-rat sequence analysis of the ICAM gene cluster on HSA 19p13.2 and a 185-kb porcine region from SSC 2q.

The human intercellular adhesion molecule gene (ICAM) cluster is located in a GC-rich and gene-rich region on HSA 19p13.2. We determined the complete DNA sequence of a 185-kb porcine bacterial artificial chromosome (BAC) clone containing parts of the ICAM gene cluster. We used the porcine sequence for a detailed comparative analysis between human, pig, mouse and rat. The 185 kb of porcine sequence covered 220 kb of homologous sequence in the human genome, which adds to the growing evidence that the porcine genome is somewhat smaller than the human genome. The genomic sequences of the four species showed a high level of conserved synteny and no rearrangements in gene order were observed. During evolution, the ICAM3 gene was inactivated by mutation in the mouse and rat genome, whereas it is still present in the human and pig genome. The loss of Icam3 in rodent genomes might be relevant for rodent-specific properties of the T-cell-mediated immune response. All the other investigated genes are conserved across all four investigated sequences.