Molecular cloning, sequence analysis, and cadmium stress-rated expression changes of BTG1 in freshwater pearl mussel(Hyriopsis schlegelii)

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 eDNA 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 eDNA ends （RACE） together with splicing the EST sequence from a haemocyte eDNA 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）. Homologne 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-BTG 1 may have played a significant role in H, schlegelii adaptation to adverse environmental conditions.

Characterization of cyclophilin D in freshwater pearl mussel (Hyriopsis schlegelii)

Cyclophilin D （referred to as HsCypD） was obtained from the freshwater pearl mussel （Hyriopsis schlegelil）. The full-length cDNA was 2 671 bp, encoding a protein consisting of 367 amino acids. HsCypD was determined to be a hydrophilic intracellular protein with 10 phosphorylation sites and four tetratricopeptide repeat （TPR） domains, but no signal peptide. The core sequence region YKGCIFHRIIKDFMVQGG is highly conserved in vertebrates and invertebrates. Phylogenetic tree analysis indicated that CypD from all species had a common origin, and HsCypD had the closest phylogenetic relationship with CypD from Lottia gigantea. The constitutive mRNA expression levels of HsCypD exhibited tissue-specific patterns, with the highest level detected in the intestines, followed by the gonads, and the lowest expression found in the hemocytes.