Extensive gene order differences within regions of conserved synteny between the Fugu and human genomes: implications for chromosomal evolution and the cloning of disease genes.

The suitability of the Fugu genome to facilitate the identification of candidate human disease genes using comparative positional cloning is dependent upon the extent to which synteny and gene order are conserved between the two species. We have cloned seven Fugu genes which are closely linked to Surfeit genes in two regions of the Fugu genome and have mapped and ordered their human homologues both by PCR analysis of the Genebridge 4 panel of radiation hybrids and by fluorescence in situ hybridization. All seven human genes map to a 3 Mb region of chromosome band 9q34.1, approximately 2-4 Mb proximal to the human Surfeit genes. Although both Fugu regions are syntenic with human chromosome band 9q34, the relative order of the genes differs greatly in the two species. Indeed, some of the genes that are adjacent in the Fugu genome are separated by at least 2-4 Mb in the human genome. This suggests that intra-chromosomal rearrangements, most probably inversions, have been common during the 900 million years of divergent evolution separating Fugu and human. The utility of Fugu to facilitate human disease gene identification by comparative positional cloning is questioned in light of these results.