3 and Notch signaling is seen. RNAi treatment of either genomic copy of the H3. 3 histone variant shows a dramatic decrease in Notch activated transcription. The histone variant H3. 3 has been shown click here to be incorporated into the promoters of actively transcribed genes in a replication independent process to maintain transcription and its influence on Notch tar geted transcription remains to be explored. A major question that arises from these data is, how specific can the identified chromatin factors be to regu lating Notch transcription It has recently been noted that chromatin components are more selective in func tion than was previously thought. Surprisingly, there are now a handful of examples where modulating the expression of a single target gene can rescue the pheno type associated with a null mutation in a chromatin remodeling complex component.

By immunopreci pitation and mass spec analysis, it has recently been shown that the Notch repressor complex contains a host of chromatin modifying components. These identified components include Sin3A, Rpd3, lid, Bap55 and moira, factors that were also uncovered in this screen as modifiers of Notch target transcription. This repressor complex has been shown to be recruited to Notch target promoters by Su and this interaction may provide a mechanism for targeting the activity of these chromatin factors to Notch signaling. This is consistent with the observation that the genetic inter actions demonstrated between this repressor complex and Notch were not seen when tested against a host of other signaling pathways.

Control reporter tran scription levels in this study indicated that targeting these chromatin genes by dsRNA did not significantly reduce cell viability and growth over the course of the five day RNAi incubation in culture. The screen data shows that Notch signaling may be particularly sensitive to the levels of these chromatin components in the cell, while the protein interaction network confirms that many of these chromatin factors physically interact with Su and Hairless suggesting a mechanism to explain this observation. Regulation of histone position and modification are known factors that determine the context dependent nature of Notch signaling during development. These factors differentially interpret the signals received from the cell surface by recording an epigenetic history on the target promoter.

This transcription based screen revealed new chromatin factors that can be further stu died for their role in Notch mediated development. mRNA processing factors The genome wide transcription assay revealed two other classes Entinostat of proteins not conventionally associated with tran scriptional regulation. A number of ribosomal components and proteins associated with mRNA processing were found to regulate transcription of the activated Notch tar get gene. What is unexpected about these interactions is their relative specificity, as was for the chromatin components.