Preliminary Study on the Rapid Evolution of MtDNA Control Region and the Elongated Mechanism of Tandem Repeat Units in Cynoglossinae Fishes

The complete control regions of mitochondrial DNA were amplified in three tongue soles Cynoglossus bilineatus(Lacepede,1802),Paraplagusia bilineata(Bloch,1787),and Paraplagusia blochii(Bleeker,1851) from subfamily Cynoglossinae,and compared with that from other four flatfishes.The length of control regions(CR) ranged from 655 to 1155 bp and exhibited apparent length heteroplasmy.Comparisons showed that the control regions have significant differences from that of other flatfishes,with only conserved blocks of CSB-A and TAS identified and higher AT content detected.It was presumed that these variations may have resulted in the fast evolution of CR regions in these tongue soles.Furthermore,the presence of tandem repeats at 5' end of control regions was detected,and these repeat units bear TAS-like sequences,which the possess capability of forming the stable secondary structure in all three tongue soles.These characteristics of control regions in those soles provide likely new evidences for the illegitimate elongation model,the elongated mechanism of tandem repeat units.Additionally,the elongation process of these tandem repeats in tongue soles was speculated using illegitimate elongation model.