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

Abstract

BackgroundForce, 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 (fabp) 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 fabp mRNA and heterogeneous nuclear RNA (hnRNA) transcripts in liver, intestine, muscle, brain and heart for four sets of duplicated fabp genes, fabp1a/fabp1b.1/fabp1b.2, fabp7a/fabp7b, fabp10a/fabp10b and fabp11a/fabp11b in zebrafish fed different concentrations of clofibrate.ResultElectron 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 acox1 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 fabp mRNA and hnRNA transcripts for the four sets of duplicated fabp 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 fabp mRNAs and hnRNAs for both the duplicated copies of fabp1a/fabp1b.1, and fabp7a/fabp7b, but in different tissues. Clofibrate also increased the steady-state level of fabp10a and fabp11a mRNAs and hnRNAs in liver, but not for fabp10b and fabp11b.ConclusionSome duplicated fabp 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 fabp genes by clofibrate has markedly diverged since the WGD event.

Fatty acid binding proteins have the potential to channel dietary fatty acids into enterocyte nuclei

“…Different fabp genes were expressed in the zebrafi sh intestine ( 41,(44)(45)(46)(47), including high transcript levels of fabp1b.1 and fabp2 and trace amounts of fabp1a and fabp1b.2 ( 44,45,47,65 ). By carefully removing the ventral white adipose tissue closely associated with the digestive tract and dissecting the anterior intestine, which is the major site of fat absorption ( 41-43 ), we retrieved similarly high transcript levels of fabp1b.1 and fabp2 and smaller amounts of fabp1b.2 , irrespective of the animals' nutritional status.…”

Chronic effects of clofibric acid in zebrafish (Danio rerio): A multigenerational study

“…CA was dosed through the diet, at nominal contents of 1 and 10 mg/g of food and the exposure period was from 5 to 140 dpf. These contents were selected based on human therapeutic doses and according to previous studies that used a similar range of bezofibrate and clofibrate contents incorporated in the diet in zebrafish (Velasco-Santamaria et al, 2011;Venkatachalam et al, 2012;Venkatachalam et al, 2013). CA was incorporated in the diet using acetone as vehicle.…”

“…Considering their effects in mammalian lipid metabolism, these pharmaceuticals might also interfere with lipid homeostasis and growth of non-target exposed animals, like fish as recently shown by the regulation of the genes coding for fatty acid-binding proteins (Venkatachalam et al, 2012;Venkatachalam et al, 2013) and the enzyme fatty acyl-coenzyme-A oxidase (FAO) involved in fatty acid oxidation (Weston et al, 2009). Previous studies on the effects of CA on the growth of fish were inconclusive as both reduced growth (Owen et al, 2010;Raldua et al, 2008) or no effects at all have been observed following exposure (Owen et al, 2010).…”

Interaction of brain fatty acid-binding protein with the polyunsaturated fatty acid environment as a potential determinant of poor prognosis in malignant glioma

“…FABPs are intracellular fatty acid binding proteins involved in the binding and the intracellular trafficking of fatty acids and retinoids to different subcellular compartments: cytoplasmic, for metabolism and energy production, or nuclear, for regulation of gene transcription via activation of peroxisome proliferator-activated receptors (PPARs) [48].…”

“…PPAR ligands have been implicated in FABP7 induction during zebrafish development, with FABP7 levels significantly induced in the liver and intestine, but not the brain, of zebrafish treated with clofibrate, a specific ligand for PPARα and to a lesser extent for PPARγ [48,63]. There is evidence suggesting that natural PPAR ligands such as fatty acids can also affect FABP7 expression.…”