The cAMP signaling pathway regulates Epe1 protein levels and heterochromatin assembly

The epigenetic landscape of a cell frequently changes in response to fluctuations in nutrient levels, but the mechanistic link is not well understood. In fission yeast, the JmjC domain protein Epe1 is critical for maintaining the heterochromatin landscape. Loss of Epe1 results in heterochromatin expansion and overexpression of Epe1 leads to defective heterochromatin. Through a genetic screen, we found that mutations in genes of the cAMP signaling pathway suppress the heterochromatin defects associated with Epe1 overexpression. We further demonstrated that the activation of Pka1, the downstream effector of cAMP signaling, is required for the efficient translation of epe1+ mRNA to maintain Epe1 overexpression. Moreover, inactivating the cAMP-signaling pathway, either through genetic mutations or glucose deprivation, leads to the reduction of endogenous Epe1 and corresponding heterochromatin changes. These results reveal the mechanism by which the cAMP signaling pathway regulates heterochromatin landscape in fission yeast. Overall design: ChIP-seq of H3K9me2 in WT cell grown in YEA or YEA low glucose media (0.1% glucose, 3% glycerol) for 6 hours.

细胞的表观遗传景观（epigenetic landscape）常会响应营养水平的波动发生改变，但其背后的机制关联尚未被充分阐明。在裂殖酵母（fission yeast）中，JmjC结构域（JmjC domain）蛋白Epe1对维持异染色质景观（heterochromatin landscape）至关重要：Epe1缺失会导致异染色质扩张，而过表达Epe1则会引发异染色质功能缺陷。通过遗传筛选（genetic screen），我们发现cAMP信号通路（cAMP signaling pathway）相关基因的突变能够抑制Epe1过表达所引发的异染色质缺陷。进一步研究证实，cAMP信号通路的下游效应因子Pka1的激活，是epe1+ mRNA高效翻译以维持Epe1过表达状态所必需的。此外，无论是通过遗传突变还是葡萄糖剥夺（glucose deprivation）来失活cAMP信号通路，均会导致内源性Epe1水平降低，并引发相应的异染色质改变。上述研究结果揭示了cAMP信号通路调控裂殖酵母异染色质景观的分子机制。整体实验设计：对在YEA培养基或低糖YEA培养基（0.1%葡萄糖，3%甘油）中培养6小时的野生型（wild type, WT）细胞进行H3K9me2的染色质免疫共沉淀测序（ChIP-seq）。