Differential expression of retinoic acid receptor mRNA during mouse embryogenesis

Retinoic acid, mediated through its receptors (RAR), exhibits striking effects on cell proliferation, differentiation, and pattern formation. At least three types of RARs (α, β, and γ) have been cloned. The ontogeny and semi-quantitated amount of three RAR mRNA were studied in mouse embryos and placentas using reverse transcriptase-polymerase chain reaction technique. The amplified cDNA products were confirmed by correct sizes, Southern blot hybridization and restriction enzyme digestion. The results show that RAR-α mRNA is constitutively expressed in the oocytes and embryos of all stages, suggesting that RAR-α is a housekeeping gene. RAR-β mRNA is present in the oocytes, becomes undetectable at the 2-cell stage when the maternal RNA is degraded, and re-expresses at morula and blastocst stages when the embryonic genome is activated. RAR-γ mRNA is not expressed until blastocyst stage. In the postimplantation embryos, no significant change in all three RAR mRNA levels was detected from day 10 through the late gestational stage (day 18). Placental tissue expressed all three RAR transcripts throughout gestation. The differential activation of these three RAR genes in the preimplantation embryos suggests RARs as the important regulators during early embryogenesis.