Cloning and characterization of microphthalmia-associated transcription factor-like gene provide insights into Cyclina sinensis clam shell melanin deposition

The reversible black shell colour change in the clam Cyclina sinensis functions as an adaptation to different environmental conditions (within or outside of muddy sediment) due to changes in the melanin redox state in the shell. The microphthalmia-associated transcription factor (MITF) is a melanocyte-specific transcription factor that is involved in the differentiation, proliferation and survival of melanocytes. In this study, the full-length cDNA sequence of the mitf-like gene was obtained from C. sinensis using RACE PCR. The mitf-like cDNA is 1725 bp in length, containing a 47 bp 5 ' untranslated region (UTR), a 1398 bp open reading frame and a 280 bp 5 ' untranslated region. The mitf-like gene contains seven exons separated by six introns, and it encodes a putative protein of 465 amino acids with a highly conserved domain of MITF containing a basic helix-loop-helix leucine zipper (bHLH-LZ). The phylogenetic analysis of amino acid sequences using neighbour-joining and maximum likelihood methods revealed that C. sinensis is closely related to Meretrix petechialis. Additionally, the mRNA expression of mitf-like and melanin was high in the outer margin of the mantle, suggesting that the mitf-like might play an important role in melanin synthesis in the mantle by regulating the cell cycle and survival of melanocytes; however, its role in C. sinensis shell melanin deposition requires further investigation.