Changes in the expression and subcellular localization of RARalpha in the rat hippocampus during postnatal development.

Retinoic acid receptors (RARs) are reported to mediate the effects of retinoid acid and participate in the maintenance of normal hippocampal function during embryonic and postnatal stages. RARalpha is the only one that has been reported to be continuously expressed among RARs in the CA1-CA3 areas of the hippocampus, at both the mRNA and the protein level. Here, we show the expression and subcellular localization of RARalpha in granule and pyramidal cells in various regions of the hippocampus during postnatal development of rats. We discovered that the expression level of RARalpha in postnatal hippocampal tissue gradually decreased over time with increasing developmental maturity of the nervous system. Moreover, the subcellular localization of RARalpha expression showed a phenomenon of intracellular translocation during the postnatal development period. This new discovery is inconsistent with a traditional viewpoint according to which RARalpha, as a nuclear transcription factor, is mainly expressed inside nucleus. This phenomenon suggests that RARalpha may have different actions during each stage of hippocampal development.