Identification and functional characterization of MRE-binding transcription factor (MTF) in Crassostrea gigas and its conserved role in metal-induced response.

The full-length cDNA that encodes the MRE-binding transcription factor (MTF) was cloned from the Pacific oyster (Crassostrea gigas) using reverse transcription polymerase chain reaction and the rapid amplification of cDNA ends. The cgMTF cDNA sequence is 2892 bp long, with a 2508 bp open reading frame that encodes an 835-amino acid polypeptide. Multiple alignment revealed that cgMTF has four putative zinc finger-like regions in cgMTF with three C2C2-type zinc fingers and one C2H2-type zinc finger. After 12 h of exposure to Cd(2+), the cgMTF mRNA level was increased in a dose-dependent manner, which then subsided with time. cgMTF stimulates the cgMT promoter reporter in the HEK293 cell line in a dose-dependent manner. When either of the metal-responsive elements (MRE1 or MRE2) of the cgMT promoter was mutated, the cgMT promoter reporter activity was significantly reduced. After the two MREs were mutated simultaneously, the promoter activity was completely abolished. In conclusion, we identified an MTF in C. gigas and revealed the presence of an evolutionarily conserved molecular mechanism for coping with environmental metal stress.