Differential expression of max and two types of c-myc genes in a tetraploid fish, the common carp (Cyprinus carpio).

We cloned the full-length cDNA of max gene from the common carp (Cyprinus carpio). The cDNA clone of carp max consists of 1209 bp and contained an ATG-initiated ORF consisting of 156 aa. The carp MAX share 76.7-93.8% aa identity with those of human, mouse, rat, chicken, Xenopus and zebrafish, respectively. The 15 bp alternative splicing was observed in the loop region of helix-loop-helix and is not previously described in mammalian max sequences. Transcripts of max gene were observed in all of the tissues of carp investigated in this study. The highest expression was found in the ovary, and the transcripts in hepatopancreas and heart were low. Two carp c-myc genes (CAM1 and CAM2) showed differential expression pattern. The expression of max was concomitant with CAM2 expression, but not with CAM1. It has been reported that MYC/MAX heterodimer as a regulator of gene expression has been maintained throughout vertebrate evolution, and the expression of c-myc has been concomitant with max expression. In addition, according to phylogenetic analysis, CAM1 is evolving faster than CAM2 after gene duplication. Therefore, this result suggests that CAM1 may evolve to obtain a new function different from c-myc.