Cloning and sequencing of complement component C9 and its linkage to DOC-2 in the pufferfish Fugu rubripes.

The Japanese pufferfish Fugu rubripes has a 400 Mb genome with high gene density and minimal non-coding complexity, and is therefore an ideal vertebrate model for sequence comparison. The identification of regions of conserved synteny between Fugu and humans would greatly accelerate the mapping and ordering of genes. Fugu C9 was cloned and sequenced as a first step in an attempt to characterize the region in Fugu homologous to human chromosome 5p13. The 11 exons of the Fugu C9 gene share 33% identity with human C9 and span 2.9 kb of genomic DNA. By comparison, human C9 spans 90 kb, representing a 30-fold difference in size. We have also determined by cosmid sequence scanning that DOC-2, a tumour suppresser gene which also maps to human 5p13, lies 6-7 kb from C9 in a head-to-head or 5' to 5' orientation. These results demonstrate that the Fugu C9/DOC-2 locus is a region of conserved synteny. Sequence scanning of overlapping cosmids has identified two other genes, GAS-1 and FBP, both of which map to human chromosome 9q22, and lie adjacent to the Fugu C9/DOC-2 locus, indicating the boundary between two syntenic regions.