Requirement of retinoic acid receptor isotypes α, β, and γ during the initial steps of neural differentiation of PCC7 cells

Retinoic acid ( RA) is indispensable for morphogenesis and differentiation of several tissues, including the nervous system. The requirement of the RA receptor (RAR) isotypes alpha, beta, and gamma and the putative role of retinoid X receptor-(RXR) signaling in RA-induced neural differentiation, was analyzed. For this compound-selective retinoids and the murine embryonal carcinoma cell line PCC7, a model system for RA-dependent neural differentiation was used. The present paper shows that proliferating PCC7 cells primarily express RXR alpha and RAR alpha, lower levels of RXR beta, and barely detectable amounts of RAR beta, RAR gamma, and RXR gamma. At receptor-selective concentrations, only a RAR alpha or RAR gamma agonist induced the typical tissue-like differentiation pattern consisting of neuronal and nonneuronal cells. Differentiation-associated processes, such as the down-regulation of Oct4, up-regulation of certain nuclear receptors and proneuronal genes, and the induction of neuronal markers could be triggered by receptor-selective concentrations of a RAR alpha-, beta-, or gamma-selective agonist, although with distinct efficacy. The differences are only partially explained by the distinct RAR alpha, beta, and gamma expression levels and the dissociation constants for the bound retinoids, suggesting differential requirement of RAR isotypes during the initial stages of neural differentiation of PCC7 cells.