Cloning of complementary deoxyribonucleic acids encoding quail (Coturnix coturnix japonica) retinoic acid receptor β isoforms and changes in their gene expression during gonadotropic growth

Retinoids have important effects on the development of the reproductive system, where they act via their specific nuclear receptors: retinoic acid receptors (RAR alpha, beta, gamma) and retinoid X receptors (RXR alpha, beta, gamma). The research reported here was conducted in an effort to clone quail RAR beta cDNA (qRAR beta) and to evaluate the expression of qRAR beta mRNAs in different tissues and during the development of gonadotropic organs. Two complete cDNAs of qRAR beta1 and qRAR beta2 were isolated by a combination of reverse transcription-polymerase chain reaction and 5'- and 3'-rapid amplification of cDNA ends techniques. An RNase protection assay revealed the widespread expression of qRAR beta1 and beta2 with large tissue-specific variations. The qRAR beta1 isoform was predominant in the testis, whereas qRAR beta2 was dominant in the other tissues examined with the exception of the brain, where both isoforms were almost equally expressed. In the developing testes, the qRAR beta1 mRNA level was high between 30 and 40 days of age, the period during which the testes grew rapidly. The level declined thereafter to its initial level. In contrast, qRAR beta2 mRNA did not exhibit obvious changes. In the developing oviducts, both qRAR beta1 and beta2 mRNAs reached their peak levels by 30 days of age, just before the rapid development of the oviduct occurred, and then decreased to almost undetectable levels when the oviduct developed to the laying stage (over 2.88 g in weight). Similar expression patterns of qRAR beta1 and beta2 were also observed in the developing follicles from the prehierarchical (<2-mm diameter) to the largest preovulatory follicle. In contrast, neither qRAR<beta>1 nor beta2 mRNA exhibited developmental changes in the brain. These results suggest that RAR beta may play an important role in the development of the reproductive systems of birds.