Extensive lineage-specific gene duplication and evolution of the spiggin multi-gene family in stickleback.
BACKGROUND
The threespine stickleback (Gasterosteus aculeatus) has a characteristic reproductive mode; mature males build nests using a secreted glue-like protein called spiggin. Although recent studies reported multiple occurrences of genes that encode this glue-like protein spiggin in threespine and ninespine sticklebacks, it is still unclear how many genes compose the spiggin multi-gene family.


RESULTS
Genome sequence analysis of threespine stickleback showed that there are at least five spiggin genes and two pseudogenes, whereas a single spiggin homolog occurs in the genomes of other fishes. Comparative genome sequence analysis demonstrated that Muc19, a single-copy mucous gene in human and mouse, is an ortholog of spiggin. Phylogenetic and molecular evolutionary analyses of these sequences suggested that an ancestral spiggin gene originated from a member of the mucin gene family as a single gene in the common ancestor of teleosts, and gene duplications of spiggin have occurred in the stickleback lineage. There was inter-population variation in the copy number of spiggin genes and positive selection on some codons, indicating that additional gene duplication/deletion events and adaptive evolution at some amino acid sites may have occurred in each stickleback population.


CONCLUSIONS
A number of spiggin genes exist in the threespine stickleback genome. Our results provide insight into the origin and dynamic evolutionary process of the spiggin multi-gene family in the threespine stickleback lineage. The dramatic evolution of genes for mucous substrates may have contributed to the generation of distinct characteristics such as "bio-glue" in vertebrates.
Kawahara
Ryouka
R
Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo 164-8639, Japan. kawaharar@ori.u-tokyo.ac.jp
Nishida
Mutsumi
M
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002874:Chromosome Mapping / Q000662:veterinary; D017124:Conserved Sequence; D019143:Evolution, Molecular; D029941:Fish Proteins / Q000235:genetics*; D017353:Gene Deletion; D018628:Gene Dosage; D020440:Gene Duplication; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009077:Mucins / Q000235:genetics; D005810:Multigene Family / Q000235:genetics*; D009990:Oryzias / Q000235:genetics; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D011544:Pseudogenes; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid; D023701:Smegmamorpha / Q000235:genetics*; D013045:Species Specificity
D029941:Fish Proteins; C482349:MUC19 protein, human; C482348:Muc19 protein, mouse; D009077:Mucins; C429543:spiggin