The B cells translocation gene 1(BTG1) is a member of the BTG/TOB family of anti-proliferative genes,which have recently emerged as important regulators of cell growth and differentiation among vertebrates.Here,for the first time we cloned the full-length cDNA sequence of Hyriopsis schlegelii(Hs-BTG1),an economically important freshwater shellfish and potential indicator of environmental heavy metal pollution,for the first time.Using rapid amplification of cDNA ends(RACE) together with splicing the EST sequence from a haemocyte cDNA library,we found that Hs-BTG1 contains a 525 bp open reading frame(ORF) encoding a 174 amino-acid polypeptide,a 306 bp 5' untranslated region(5' UTR),and a 571 bp 3' UTR with a Poly(A) tail as well as a transcription termination signal(AATAAA).Homologue searching against GenBank revealed that Hs-BTG1 was closest to Crassostrea gigas BTG1,sharing 50.57% of protein identities.Hs-BTG1 also shares some typical features of the BTG/TOB family,possessing two well-conserved A and B boxes.Clustering analysis of Hs-BTG1 and other known BTGs showed that Hs-BTG1 was also closely related to BTG1 of C.gigas from the invertebrate BTG1 clade.Function prediction via homology modeling showed that both Hs-BTG1 and C.gigas BTG1 share a similar three-dimensional structure with Homo sapiens BTG1.Tissue-specific expression analysis of the Hs-BTG1 via real-time PCR showed that the transcripts were constitutively expressed,with the highest levels in the hepatopancreas and gills,and the lowest in both haemocyte and muscle tissue.Expression levels of Hs-BTG1 in hepatopancreas(2.03-fold),mantle(2.07-fold),kidney(2.2-fold) and haemocyte(2.5-fold) were enhanced by cadmium(Cd2+) stress,suggesting that Hs-BTG1 may have played a significant role in H.schlegelii adaptation to adverse environmental conditions.
Kou PENGCheng-Yuan WANGJun-Hua WANGJun-Qing SHENGJian-Wu SHIJian LIYi-Jiang HONG
