Cloning and expression pattern of peroxisome proliferator-activated receptors, estrogen receptor α and retinoid X receptor α in the thicklip grey mullet Chelon labrosus

Aquatic organisms are exposed to diverse xenobiotics that cause peroxisome proliferation and/or endocrine disruption, both modulated in vertebrates by transcription factors of the nuclear receptor (NR) superfamily. Peroxisome proliferators are agonists of peroxisome proliferator-activated receptors (PPARs) that heterodimerize with the retinoid X receptor (RXR). Many xenoestrogens activate the estrogen receptor (ER). Here, 1090 bp of PPARα, 1255 bp of PPARγ, 278 bp of RXRα, and 578 bp of ERα of thicklip grey mullet Chelon labrosus were cloned. Sequences were highly conserved, although relevant changes with respect to mammalian homologs were identified in PPARγ and ERα. Semi-quantitative RT-PCR was used to determine if these NRs were expressed in different tissues of male, female and undifferentiated mullets captured in January and June. Expression of PPARs was highest in liver and lowest in muscle. RXRα expression was homogeneous excepting a low expression in male and female gill in January and brain and heart of undifferentiated fish in January and June. ERα expression predominated in liver and female gonad in June. The expression level of PPARs and ERα was significantly higher in liver in January than in gills in January or June. The present results show tissue-dependent modulation of expression of NRs in mullets.