Genetic characteristics and evolution of Pitx2 in sinistral tongue sole,cynoglossus semilaevis and dextral stone flounder,Kareius bicoloratus

The nodal signaling pathway downstream transcription target pitx2 has been found to be involved in determination of left-right (l-r) asymmetry in the mouse,chick and xenopus embryos. however,the genetic characteristic and evolution of pitx2 has rarely been reported in marine fish. in our study,we cloned and analyzed the structure of pitx2 in tongue sole (cynoglossus semilaevis) (cs-pitx2) and stone flounder (kareius bicoloratus) (kbpitx2). phylogenetic and sequences analysis showed that cs-pitx2 and kb-pitx2 had high identity,and homologous to the pitx2 of other vertebrates. a low ka/ks ratio showed that pitx2 evolving was under purifying selection. there are several basal core promoter elements and transcription factor binding sites in the promoter region of cs-pitx2. quantitative rt-pcr analysis showed that the expression of pitx2 increased during the developmental stages. interestingly,the expression of pitx2 in sinistral tongue sole was much higher than in dextral flatfish stone flounder during metamorphosis,which might be one of the reasons of different deflecting direction of them. these data provide the evidence that pitx2 was a crucial nodal signaling pathway gene that might mediate l-r asymmetry in flatfish. copyright 2015 zoological society of pakistan.