Regulation of RAR-b and RXR-c in Schwann Cells Figure 8. Transcriptional regulation of RAR-b and RXR-c by RA. (A) The levels of newly synthesized hnRNA for RAR-b and RXR-c were determined by RT-Q-PCR in myelinating cocultures treated with 1 mM RA for the indicated times. All values are shown as the mean 6 SD relative to their respective controls. (B) Newly synthesized RAR-b and RXR-c hnRNA was determined in isolated SCs treated or not with 1 mM RA for 48 hours. All values are shown as the mean 6 SD relative to their respective controls. (C) SCs were treated with 1 mM RA in combination or not with the axonal mimickers forskolin and BPE for 24 hours in the presence or absence of 10 mg/ml of the protein synthesis inhibitor cycloheximide (CHX), and RAR-b and RXR-c mRNA levels were determined by Q-RT-PCR. All values are shown as the mean 6 SEM relative to their respective controls in the absence of cycloheximide and retinoic acid. (D) Isolated SCs were pretreated or not with 1 mM RA for 24 hours and the stability of RAR-b and RXR-c mRNA was determined by incubating the cells with 10 mg/ml actinomycin D for varying times in the continuous presence or not of the retinoid. All values are shown as the mean 6 SD relative to their respective time zero. RA-treated cells presented RAR-b mRNA levels 59 times higher than control cells, while RXR-c levels were only 40% of those from control cultures. doi:10.1371/journal.pone.0017023.g008 RXR-c expression is developmentally regulated during periph- eral nervous system development in rodents [53]. While in chicken embryos RXR-c is expressed from the onset of neural crest migration [54], rat RXR-c expression is not detectable in dorsal root and trigeminal ganglia until 14.5 days post coitum, suggesting a role for this nuclear receptor in DRGs of late embryos. The in situ hybridization technique does not allow discrimination on the nature of the cell types that express RXR-c in the ganglia, although the same authors already reported a comparatively very high RXR-c expression level in 7-day-old rats. The detection onset of RXR-c in these ganglia coincides with the period during which they begin to innervate their peripheral and central targets. Interestingly, until 10.5 dpc, Egr2 expression in peripheral nerves is restricted to the proximities of the ganglia, but at 15.5 there is a dramatic activation of Egr2 expression being reported along the whole sciatic nerve [55]. This stage corresponds precisely to the period of the transition from precursors to embryonic Schwann cells [56], a transition that involves the activation of Egr2 [44]. PLoS ONE | www.plosone.org 10 February 2011 | Volume 6 | Issue 2 | e17023