Role of TGF-beta in RA-induced cleft palate in CD-1 mice

Retinoic acid (RA) plays an important role in embryogenesis, by regulating morphogenesis, cell proliferation, differentiation, and extracellular matrix production. RA exposure on gestational day (GD) 12 in CD-1 mice results in delayed palatal shelf elevation and subsequent clefts in the secondary palate. Given the dynamic and complex nature of palate development, it is not surprising that this system is susceptible to changes in retinoid levels. There is evidence that experimental manipulation of retinoid status during development alters normal transforming growth factor-beta (TGF-beta) status. To study the role of perturbation in TGF-beta levels in RA-induced cleft palate, gravid CD-1 mice were treated with 70 mg/kg RA on GD 12. We examined changes in TGF-beta proteins and the steady-state level of TGF-beta mRNA within the first 24 hr after exposure. The interactions between RA and TGF-beta s were very complex. RA differentially regulated the mRNA and protein levels of TGF-beta 1. Changes in mRNA steady-state levels were rapid and transient in nature, indicating a direct mediation by RA. Differential regulation was evident, because RA treatment resulted in an increase in TGF-beta 1 mRNA steady levels followed by a decrease in the intracellular and extracellular forms of TGF-beta 1 protein. Moreover, the patterns of localization and levels of TGF-beta 2 and TGF-beta 3 proteins were not dramatically affected, although there was an increase in TGF-beta 3 mRNA steady-state levels. The increases in mRNA steady-state levels for TGF-beta 2 and TGF-beta 3, as for TGF-beta 1, were rapid and transient in nature, again arguing for direct mediation by RA. These data provide evidence for interactions between RA and TGF-beta s, and indicate that RA is capable of differentially regulating TGF-beta isoforms through processes involving different stages of TGF-beta synthesis and secretion. Further, changes in TGF-beta isoforms were observed prior to changes in mesenchyme morphology and must be considered as mediators of RA's effects on mesenchyme development.