Tissue-specific differential induction of duplicated fatty acid-binding protein genes by the peroxisome proliferator, clofibrate, in zebrafish (<it>Danio rerio</it>)

• Main Authors: Venkatachalam Ananda B, Lall Santosh P, Denovan-Wright Eileen M, Wright Jonathan M
• Format: Article
• Language: English
• Published: BMC 2012-07-01
• Series: BMC Evolutionary Biology
• Online Access: http://www.biomedcentral.com/1471-2148/12/112

<p>Abstract</p> <p>Background</p> <p>Force, Lynch and Conery proposed the duplication-degeneration-complementation (DDC) model in which partitioning of ancestral functions (subfunctionalization) and acquisition of novel functions (neofunctionalization) were the two primary mechanisms for the retention of duplicated genes. The DDC model was tested by analyzing the transcriptional induction of the duplicated fatty acid-binding protein (<it>fabp</it>) genes by clofibrate in zebrafish. Clofibrate is a specific ligand of the peroxisome proliferator-activated receptor (PPAR); it activates PPAR which then binds to a peroxisome proliferator response element (PPRE) to induce the transcriptional initiation of genes primarily involved in lipid homeostasis. Zebrafish was chosen as our model organism as it has many duplicated genes owing to a whole genome duplication (WGD) event that occurred ~230-400 million years ago in the teleost fish lineage. We assayed the steady-state levels of <it>fabp</it> mRNA and heterogeneous nuclear RNA (hnRNA) transcripts in liver, intestine, muscle, brain and heart for four sets of duplicated <it>fabp</it> genes, <it>fabp1a/fabp1b.1/fabp1b.2, fabp7a/fabp7b, fabp10a/fabp10b</it> and <it>fabp11a/fabp11b</it> in zebrafish fed different concentrations of clofibrate.</p> <p>Result</p> <p>Electron microscopy showed an increase in the number of peroxisomes and mitochondria in liver and heart, respectively, in zebrafish fed clofibrate. Clofibrate also increased the steady-state level of <it>acox1</it> mRNA and hnRNA transcripts in different tissues, a gene with a functional PPRE. These results demonstrate that zebrafish is responsive to clofibrate, unlike some other fishes. The levels of <it>fabp</it> mRNA and hnRNA transcripts for the four sets of duplicated <it>fabp</it> genes was determined by reverse transcription, quantitative polymerase chain reaction (RT-qPCR). The level of hnRNA coded by a gene is an indirect estimate of the rate of transcriptional initiation of that gene. Clofibrate increased the steady-state level of <it>fabp</it> mRNAs and hnRNAs for both the duplicated copies of <it>fabp1a/fabp1b.1,</it> and <it>fabp7a/fabp7b</it>, but in different tissues. Clofibrate also increased the steady-state level of <it>fabp10a</it> and <it>fabp11a</it> mRNAs and hnRNAs in liver<it>,</it> but not for <it>fabp10b</it> and <it>fabp11b</it>.</p> <p>Conclusion</p> <p>Some duplicated <it>fabp</it> genes have, most likely, retained PPREs, but induction by clofibrate is over-ridden by an, as yet, unknown tissue-specific mechanism(s). Regardless of the tissue-specific mechanism(s), transcriptional control of duplicated zebrafish <it>fabp</it> genes by clofibrate has markedly diverged since the WGD event.</p>