Origin of a novel protein-coding gene family with similar signal sequence in Schistosoma japonicum.
BACKGROUND
Evolution of novel protein-coding genes is the bedrock of adaptive evolution. Recently, we identified six protein-coding genes with similar signal sequence from Schistosoma japonicum egg stage mRNA using signal sequence trap (SST). To find the mechanism underlying the origination of these genes with similar core promoter regions and signal sequence, we adopted an integrated approach utilizing whole genome, transcriptome and proteome database BLAST queries, other bioinformatics tools, and molecular analyses.


RESULTS
Our data, in combination with database analyses showed evidences of expression of these genes both at the mRNA and protein levels exclusively in all developmental stages of S. japonicum. The signal sequence motif was identified in 27 distinct S. japonicum UniGene entries with multiple mRNA transcripts, and in 34 genome contigs distributed within 18 scaffolds with evidence of genome-wide dispersion. No homolog of these genes or similar domain was found in deposited data from any other organism. We observed preponderance of flanking repetitive elements (REs), albeit partial copies, especially of the RTE-like and Perere class at either side of the duplication source locus. The role of REs as major mediators of DNA-level recombination leading to dispersive duplication is discussed with evidence from our analyses. We also identified a stepwise pathway towards functional selection in evolving genes by alternative splicing. Equally, the possible transcription models of some protein-coding representatives of the duplicons are presented with evidence of expression in vitro.


CONCLUSIONS
Our findings contribute to the accumulating evidence of the role of REs in the generation of evolutionary novelties in organisms' genomes.
Department of Immunogenetics, Institute of Tropical Medicine (NEKKEN), and Global COE Program, Nagasaki University, 1-12-4 Sakamoto, 852-8523, Nagasaki, Japan.
Evaristus Chibunna
EC
Mbanefo
Yu
Y
Chuanxin
Mihoko
M
Kikuchi
Mohammed Nasir
MN
Shuaibu
Daniel
D
Boamah
Masashi
M
Kirinoki
Naoko
N
Hayashi
Yuichi
Y
Chigusa
Yoshio
Y
Osada
Shinjiro
S
Hamano
Kenji
K
Hirayama
D017398:Alternative Splicing / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015139:Blotting, Southern; D003198:Computer Simulation; D018076:DNA, Complementary / Q000235:genetics; D019143:Evolution, Molecular; D020440:Gene Duplication / Q000235:genetics; D020131:Genes, Duplicate / Q000235:genetics; D017238:Genes, Helminth / Q000235:genetics*; D056426:Genetic Loci / Q000235:genetics; D049751:Genome, Helminth / Q000235:genetics; D015801:Helminth Proteins / Q000737:chemistry / Q000235:genetics; D008957:Models, Genetic; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics*; D016366:Open Reading Frames / Q000235:genetics*; D010802:Phylogeny; D021382:Protein Sorting Signals / Q000235:genetics*; D015183:Restriction Mapping; D012549:Schistosoma japonicum / Q000235:genetics*; D016415:Sequence Alignment; D013045:Species Specificity
D018076:DNA, Complementary; D015801:Helminth Proteins; D021382:Protein Sorting Signals