Effects of LXR activation in zebrafish larvae

The Liver X Receptors (LXRs) play important roles in multiple metabolic pathways, including fatty acid, cholesterol, carbohydrate and energy metabolism. To expand the knowledge of the functions of LXR signaling during embryonic development, we performed a whole-genome microarray analysis of Lxr target genes in zebrafish larvae treated with either one of the synthetic LXR ligands T0901317 or GW3965. Assessment of the biological processes enriched by differentially expressed genes revealed a prime role for Lxr in regulating lipid metabolic processes, similarly to the function of LXR in mammals. In addition, exposure to the Lxr ligands induced changes in expression of genes in the neural retina and lens of the zebrafish eye, including the photoreceptor guanylate cyclase activators and lens gamma crystallins, suggesting a potential novel role for Lxr in modulating the transcription of genes associated with visual function in zebrafish. The regulation of expression of metabolic genes was phenotypically reflected in an increased absorption of yolk in the zebrafish larvae, and changes in the expression of genes involved in visual perception were associated with morphological alterations in the retina and lens of the developing zebrafish eye. The regulation of expression of both lipid metabolic and eye specific genes was sustained in 1 month old fish. The transcriptional networks demonstrated several conserved effects of LXR activation between zebrafish and mammals, and also identified potential novel functions of Lxr, supporting zebrafish as a promising model for investigating the role of Lxr during development. Wild type zebrafish WIK embryos were collected after spawning. At 4 days post fertilization (dpf), zebrafish larvae were transferred to 6-well plates (pools of 30 embryos/well) in 3 mL of embryo media (E3: 5 mM NaCl, 0.17 mM KCl, 0.33 mM CaCl2, 0.3 mM MgSO4). Larvae at 4 dpf were treated with DMSO as vehicle control, 2 mM T0901317 (T0) or 1 mM GW3965 (GW). Final DMSO concentration in all treatments and control was 0.1%. Treatments were renewed after 24 h and larvae were collected for RNA extraction at 6 dpf. Treatments with vehicle (0.1% DMSO), T0 and GW were performed in biological quadruplicates of pools of RNA. Array corresponding to sample 33576 (T0 treatment replicate 2) was excluded from microarray data analysis.