At this time, is expressed at its highest levels (Fig. to promote ES cell self-renewal, once cells have experienced a period of such signals, subsequent inhibition of Fgf signalling has the opposite effect and drives differentiation. We further show in the embryo that retinoid repression of Fgf signalling promotes neural differentiation onset in an analogous step in the extending embryonic body axis and so identify attenuation of Fgf signalling by retinoic acid as a conserved fundamental mechanism driving differentiation towards somatic cell fates. in ES cells (Gu et al., 2005) and that it might work directly via a retinoic acid response element (RARE) in the promoter, as has been reported in P19 EC cells (Barnea and Bergman, 2000; Okazawa et al., 1991; Pikarsky et al., 1994). This may be one way in which RA influences Fgf signalling during differentiation, as Oct4 together with Clobetasol propionate Sox2 promotes expression in ES cells (Yuan et al., 1995). Fgf4 is the principal source of Erk signalling in differentiating mES cells, as indicated by reduced dP-Erk levels and the poor differentiation of as cells leave the tailbud (reviewed by Wilson et al., 2009); a step that may be analogous to RA-mediated downregulation of in ES cells. Furthermore, RA and Fgf pathways are mutually inhibitory in the embryonic axis (Diez del Corral et al., 2003), and elevated Fgf or reduced RA Clobetasol propionate signalling is characteristic of many cancerous cell states (reviewed by Diez del Corral and Storey, 2004). These studies therefore suggest that RA attenuation of Fgf signalling is a fundamental signalling mechanism controlling cellular differentiation. In other contexts, however, RA can promote transcription, for example, in neurula-stage Clobetasol propionate frog embryos (Moreno and Kintner, 2004). There is also evidence that RA receptors (RARs) can bind upstream elements (Brondani et al., 2002; Zhao et al., 2009), indicating that RA might directly regulate induction. However, RA exposure also gradually represses and we reveal that, once cells have experienced a period of endogenous Fgf/Erk signalling and have acquired a primitive ectoderm-like state, RA treatment inhibits Erk activity. We show that inhibition of Fgfr signalling, rather than promoting self-renewal as it does in ES cells, now mimics the ability of RA to promote neural, or in the presence of Bmp4, non-neural differentiation, and that an analogous regulatory step initiates neural differentiation in the embryonic body axis. MATERIALS AND METHODS ES cell culture Cells were grown, maintained and differentiated as described previously (Stavridis et al., 2007). 46C ES cells (expressing Sox1-GFP) were kindly provided by Austin Smith (University of Cambridge, UK) and Rex1-GFP/Oct4::CFP cells were generously provided by Hitoshi Niwa, Riken CDB (Toyooka et al., 2008). All-trans RA (Sigma) was used at 5 nM unless stated otherwise and Bmp4 (R&D Systems) at 10 ng/ml. PD173074 (Mohammadi et al., 1998; Mohammadi et al., 1997) (a kind gift of Pfizer) was added at 0.25 M. RAR and RXR antagonists “type”:”entrez-nucleotide”,”attrs”:”text”:”LG100815″,”term_id”:”1041427054″,”term_text”:”LG100815″LG100815 and “type”:”entrez-nucleotide”,”attrs”:”text”:”LG101208″,”term_id”:”1041427845″,”term_text”:”LG101208″LG101208 (Sockanathan and Jessell, 1998) were a kind gift of Ligand Pharmaceuticals and were used at 0.5 M. Cell viability was assessed following all inhibitor treatments by the proportion of non-viable cells staining with To-Pro3 in flow cytometry experiments. The Fgf8-blocking antibody and isotype control were supplied by R&D Systems (MAB323 and Clobetasol propionate MAB002, respectively). Immunoblotting Immunoblotting was performed as described previously (Stavridis et al., 2007). All total outcomes proven are representative of three or even more tests, unless stated usually. Antibodies utilized had been: anti-Crabp1 (Affinity Bioreagents, #MA3-813); anti–tubulin (Abcam, #stomach7291); anti-phospho-Erk1/2 (Thr202/Tyr204; FGF6 #9101), anti-Histone-H3 (#9717) and anti-total-Erk1/2 (#9102), all from Cell Signaling Technology. Supplementary antibodies for fluorescence immunoblotting had been 610132121 (Rockland) and A21109 (Invitrogen). Membranes Clobetasol propionate had been scanned on the LiCor scanning device and analysed with Odyssey software program. Immunocytochemistry Immunocytochemistry was performed as defined in Kunath et al. (Kunath et al., 2007). Antibodies utilized were the following: anti-Oct4 Santa Cruz (#sc-8628); LE61 supernatant (against keratins 8/18), supplied by Birgit Street (School of Dundee, UK), utilized nice on methanol-fixed examples;.