In this case, simply using cyclopamine to inhibit endogenous SHH signaling was sufficient for producing a dorsal fate shift. Human ESC-derived telencephalic cells, in contrast, seem to have a stricter tendency toward dorsal fates, whether derived with SFEB, SFEBq, or EB-based methods (Eiraku et al., 2008, Li et al., 2009 and Watanabe et al., 2007). SHH treatment alone had a pronounced, though partial, effect on repressing Pax6 and inducing Nkx2.1 in the SFEB system for hESCs (Watanabe et al., 2007), whereas ABT-199 concentration in the EB-based system the combined use of SHH and the Wnt inhibitor Dkk1 achieved a more complete
shift toward ventral fates (Li et al., 2009). Li et al. (2009) began to address the molecular mechanisms behind Screening Library cell assay the apparent predisposition of human pluripotent cells to adopt dorsal telencephalic fates. During the second week of differentiation, they reported robust induction
of Wnt ligands and Gli3 repressor. Exogenous Wnt treatments tripled the expression of Pax6 and Emx1 and doubled the expression of Gli3 repressor. Treatment with SHH attenuated the posttranslational processing of Gli3 to its repressor form. The combined effects of SHH treatment and Wnt inhibition with Dkk1 produced a nearly complete reversal from dorsal to ventral specification. Subregional patterning in the telencephalon develops in response to varying levels of morphogens that are secreted by signaling centers at
discrete locations around the forebrain (Figure 1C). Most notably, the cortical hem is positioned caudodorsally and secretes multiple Wnt and MycoClean Mycoplasma Removal Kit BMP ligands: the anterior neural ridge is positioned rostrally and secretes FGFs, and ventral aspects of the telencephalon produce SHH (Grove et al., 1998, Hébert and Fishell, 2008, Hoch et al., 2009, Ohkubo et al., 2002, Shimamura and Rubenstein, 1997, Shimogori et al., 2004 and Sur and Rubenstein, 2005). Additionally, the region of the pallial-subpallial boundary expresses neuregulins, TGF-α, the Wnt inhibitor Sfrp2, FGF15, and Spry2 (a repressor of Fgf-signaling) (Assimacopoulos et al., 2003, Faedo et al., 2010 and Subramanian et al., 2009). FGF15 and Spry2 expression from this region are implicated in regulating patterning and proliferation of the ventral cortex through controlling Coup-TF1 expression (Borello et al., 2008 and Faedo et al., 2010). In the cortex, areal patterning is established by the graded expression of key transcription factors in the dorsal telencephalon, with Emx2, Coup-TF1, Sp8, and Pax6 being the most well characterized (O’Leary et al., 2007) (Figure 1C). Emx2 is expressed in a high caudodorsal to low rostroventral gradient, and Pax6 expression is the opposite; Sp8 is expressed in a high rostrodorsal to low caudoventral gradient, and Coup-TF1 expression is the opposite.