As shown previously, a 24hour treatment with TSA just before bFGF withdrawal was sufficient to promote astrogliogenesis selleck chem inhibitor and inhibit the birth of neurons and oligodendrocytes in GE derived precursor cultures. Together with the results from gene expression profiling it can be assumed that a short treatment with TSA stimulates these cell fate decisions through epigenetic modification that lead to the up and downregulation of the corresponding developmental genes, though it is also possible that the effect does not occur at the transcriptional level, but rather through acetyl ation of cytoplasmic or nuclear non histone proteins. The stronger correlation in the 24 h gene expression data set between TSA and BMP2 treated cultures re veals that even if the early gene expression response to the treatment differs dramatically, similar downstream processes are induced, resulting in a comparable cell fate phenotype.

BMPs can enhance neurogenesis or gliogenesis de pending upon the developmental stage or brain local ization. During mid gestation BMPs are neurogenic, whereas in late prenatal and postnatal stages they are astrogliogenic. The data from gene expression pro filing revealed however a surprising downregulation of BMP signaling genes after TSA or BMP2 treatment. Bmp4 and the receptors Bmpr1a and Bmpr1b were sig nificantly downregulated in response to TSA, whereas BMP signaling inhibitors, like Bambi, Ctgf and Fst, were significantly up regulated. Only the BMP signaling inhibitor Smad7 was significantly downregulated after TSA treatment.

This indicates that both TSA and BMP2 initiate both a direct, positive response activating the downstream BMP signal ing pathway as well as a subsequent negative feedback loop that results in induction of BMP signaling inhibi tors and downregulation of BMP4 and its receptors. This clear inactivation of further BMP signaling could reflect the transition between differentiation states, which requires changes in sensitivity to BMP signals. Sensitivity to growth Brefeldin_A factors as well as the duration of signals plays an important role for BMP and TGF beta family signaling in development. Established mechanisms include select ive expression and degradation of receptors and in par ticular a range of mechanisms to control the duration of the signal of activated regulatory Smads through negative feedback mechanisms, including expression of inhibitor Smads and de phosphorylation and degradation of regulatory Smads. Interestingly, our gene expression profiling did not show an increase in astrocyte specific genes. Classic mark ers known to be upregulated during astrocyte differenti ation were either not regulated or were downregulated.