Divergent evolution of cis -acting peroxisome proliferator-activated receptor elements that differentially control the tandemly duplicated fatty acid-binding protein genes, fabp1b.1 and fabp1b.2, in zebrafish

Gene duplication is thought to facilitate increasing complexity in the evolution of life. The fate of most duplicated genes is nonfunctionalization: functional decay resulting from the accumulation of mutations. According to the duplication-degeneration-complementation (DDC) model, duplicated genes are retained by subfunctionalization, where the functions of the ancestral gene are sub-divided between duplicate genes, or by neofunctionalization, where one of the duplicates acquires a new function. Here, we report the differential regulation of the zebrafish tandemly duplicated fatty acid-binding protein genes, fabp1b.1 and fabp1b.2, by peroxisome proliferator-activated receptors (PPAR). fabp1b.1 mRNA levels were induced in tissue explants of liver, but not intestine, by PPAR agonists. fabp1b.1 promoter activity was induced to a greater extent by rosiglitazone (PPARγ-selective agonist) compared to WY 14,643 (PPARα-selective agonist) in HEK293A cells. Mutation of a peroxisome proliferator response element (PPRE) at-1232 bp in the fabp1b.1 promoter reduced PPAR-dependent activation. fabp1b.2 promoter activity was not affected by PPAR agonists. Differential regulation of the duplicated fabp1b promoters may be the result of PPRE loss in fabp1b.2 during a meiotic crossing-over event. Retention of PPAR inducibility in fabp1b.1 and not fabp1b.2 suggests unique regulation and function of the fabp1b duplicates.