Histochemical localization of retinoic acid receptors in the developing hamster fetus

Retinoids have pleiotropic effects on animal development. The eventual targets of retinoids are retinoic acid receptors (RARs). Therefore, developmental expression patterns of RARs are important in elucidating the mechanisms of normal functions of retinoids and retinoid-induced teratogenesis. We developed monospecific polyclonal antibodies against hRAR alpha, hRAR beta, and mRAR gamma, to study the developmental expression of RARs in hamster fetus. There was high sequence homology across the species for each subtype of RARs and antibodies raised against human or mouse RARs reacted with hamster RARs. In addition, hamster cDNA of RARs, which can generate the whole length antisense RNA probe using a suitable vector, were also isolated from a 12-day-old hamster fetal library. Monospecific antibodies and antisense RNA probes were used to localize proteins and transcripts of RARs in the developing hamster fetus from day 8 to day 14. There was a widespread distribution of RAR proteins and transcripts in the developing fetus. Expression was abundant in neuroepithelium, branchial arch, cardiac linings, and primordial bone and cartilage tissues. Overlapping expression and redundancy of various RARs may be one of the safeguard mechanisms in retinoid homeostasis.