Thyroid hormone receptor-β gene expression in the brain of the frog Pelophylax esculentus: Seasonal, hormonal and temperature regulation
2012
Santillo, Alessandra | Burrone, Lavinia | Ferrara, Diana | Minucci, Sergio | Pinelli, Claudia | Chieffi Baccari, Gabriella
Thyroid hormone receptor-β (trβ) cDNA was identified in the adult of Pelophylax esculentus (previously: Rana esculenta), a seasonally breeding species, in order to detect spatial brain trβ expression, its levels through the seasons and in response to 6-n-propyl-2-thiouracil, T₄ and T₃ administrations as well as to thermal manipulations. The deduced amino acid sequence of P. esculentus trβ showed a high similarity to the homologous of other vertebrates. By in situ hybridization we found trβ mRNA signal in the anterior preoptic nucleus, the habenulae, the hypothalamic-pituitary region and the ependyma. Brain trβ transcript levels varied through the seasons, and they were well correlated with brain T₄ levels but only partially with T₃ levels. Experimentally-induced hypothyroidism decreased brain trβ expression. The administration of exogenous thyroid hormones increased brain trβ expression, with T₄ appearing more potent than T₃. The experiments of thermal manipulations further strengthen the hypothesis that T₄ is more effective than T₃ in brain trβ regulation. This study also shows that, as in other vertebrates, deiodinase enzymes could modulate trβ expression via thyroid hormone regulation.
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