Thyroid hormone receptor-β gene expression in the brain of the frog Pelophylax esculentus: Seasonal, hormonal and temperature regulation

Thyroid hormone receptor-beta (tr beta) cDNA was identified in the adult of Pelophylax esculentus (previously: Rana esculenta), a seasonally breeding species, in order to detect spatial brain tr beta expression, its levels through the seasons and in response to 6-n-propyl-2-thiouracil, T-4 and T-3 administrations as well as to thermal manipulations. The deduced amino acid sequence of P. esculentus tr beta showed a high similarity to the homologous of other vertebrates. By in situ hybridization we found tr beta mRNA signal in the anterior preoptic nucleus, the habenulae, the hypothalamic-pituitary region and the ependyma. Brain tr beta transcript levels varied through the seasons, and they were well correlated with brain T-4 levels but only partially with T-3 levels. Experimentally-induced hypothyroidism decreased brain tr beta expression. The administration of exogenous thyroid hormones increased brain tr beta expression, with T-4 appearing more potent than T-3. The experiments of thermal manipulations further strengthen the hypothesis that T-4 is more effective than T-3 in brain tr beta regulation. This study also shows that, as in other vertebrates, deiodinase enzymes could modulate tr beta expression via thyroid hormone regulation. (c) 2012 Published by Elsevier Inc.