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Mesenchymal cell proliferation is critical for the growth of the palate shelf. All-trans retinoic acid (atRA), as well as pathways associated with TGF-β/Smad signaling, play crucial roles in the proliferation of mouse embryonic palate mesenchymal (MEPM) cells. We have found that MEPM-cell proliferation was regulated by atRA and exogenous TGF-β3 could significantly antagonize the atRA-mediated suppression of MEPM cell proliferation, which is closely associated with the regulation of TGF-β/Smad signaling pathway. The long non-coding RNA (lncRNA) MEG3 has been reported to activate TGF-β/Smad signaling, thereby regulating cellular proliferation, differentiation, and related processes. Here, we found that Meg3 expression increased significantly in atRA-treated MEPM cells while TGF-β3 treatment markedly inhibited Meg3 expression and antagonized the effect of atRA on Meg3. Moreover, Smad2 was found to interact directly with Meg3, and atRA treatment significantly enriched Meg3 in Smad2-immunoprecipitated samples. After Meg3 deletion, the effects of atRA on the proliferation of MEPM cells and TGF-β3-dependent protein expression were lost. Hence, we speculate that Meg3 has a role in the RA-induced suppression of MEPM cell proliferation by targeting Smad2 and thereby mediating TGF-β/Smad signaling inhibition., (Copyright © 2021 Elsevier Inc. All rights reserved.)

The role of LncRNA Meg3 in atRA-induced cleft palate involved the Smad pathway. • All-trans retinoic acid (atRA) enhanced Meg3 expression in MEPM cells. • Meg3 was linked to the suppression of MEPM cell proliferation. • AtRA treatment was associated with the demethylation of CpG sites in the Meg3 promoter. • Smad2 is a Meg3 target in the context of atRA-induced cleft palate. Palatal mesenchymal cell proliferation is essential to the process of palatogenesis, and the proliferation of mouse embryonic palate mesenchymal (MEPM) cells is impacted by both all-trans retinoic acid (atRA) and the TGF-β/Smad signaling pathway. The long non-coding RNA (lncRNA) MEG3 has been shown to activate TGF-β/Smad signaling and to thereby regulate cell proliferation, differentiation, and related processes. Herein, we found that atRA treatment (100 mg/kg) promoted Meg3 upregulation in MEPM cells, and that such upregulation was linked to the suppression of MEPM cell proliferation in the context of secondary palate fusion on gestational day (GD) 13 and 14. Moreover, the demethylation of specific CpG sites within the lncRNA Meg3 promoter was detected in atRA-treated MEPM cells, likely explaining the observed upregulation of this lncRNA. Smad signaling was also suppressed by atRA treatment in these cells, and RNA immunoprecipitation analyses revealed that Smad2 can directly interact with Meg3 in MEPM cells following atRA treatment. Therefore, we propose a model wherein Meg3 is involved in the suppression of MEPM cell proliferation, functioning at least in part via interacting with the Smad2 protein and thereby suppressing Smad signaling in the context of atRA-induced cleft palate. [ABSTRACT FROM AUTHOR]