Selective gene silencing is key to development. It is generally accepted that H3K27me3-enriched heterochromatin maintains transcriptional repression established during early development and regulates cell fate. Conversely, H3K9me3-enriched heterochromatin prevents differentiation but constitutes protection against transposable elements. We exploited the fungus Podospora anserina, a valuable alternative to higher eukaryote models, to question the biological relevance and functional interplay of these two distinct heterochromatin conformations. We established genome-wide patterns of H3K27me3 and H3K9me3 modifications, and found these marks mutually exclusive within gene-rich regions but not within repeats. We generated the corresponding histone methyltransferase null mutants and showed an interdependence of H3K9me3 and H3K27me3 marks. Indeed, removal of the PaKmt6 EZH2-like enzyme resulted not only in loss of H3K27me3 but also in significant H3K9me3 reduction. Similarly, removal of PaKmt1 SU(VAR)3–9-like enzyme caused loss of H3K9me3 and substantial decrease of H3K27me3. Removal of the H3K9me binding protein PaHP1 provided further support to the notion that each type of heterochromatin requires the presence of the other. We also established that P. anserina developmental programs require H3K27me3-mediated silencing, since loss of the PaKmt6 EZH2-like enzyme caused severe defects in most aspects of the life cycle including growth, differentiation processes and sexual reproduction, whereas loss of the PaKmt1 SU(VAR)3–9-like enzyme resulted only in marginal defects, similar to loss of PaHP1. Our findings support a conserved function of the PRC2 complex in fungal development. However, we uncovered an intriguing evolutionary fluidity in the repressive histone deposition machinery, which challenges canonical definitions of constitutive and facultative heterochromatin.

中文翻译：

---

EZH2 样或 SU(VAR)3-9 样蛋白的缺失导致 H3K27 和 H3K9 三甲基化同时受到扰动，并导致真菌 Podospora anserina 的相关发育缺陷


选择性基因沉默是发育的关键。人们普遍认为，富含 H3K27me3 的异染色质维持早期发育过程中建立的转录抑制并调节细胞命运。相反，富含 H3K9me3 的异染色质可防止分化，但构成针对转座因子的保护。我们利用真菌鹅足孢菌（Podospora anserina）（一种高等真核生物模型的有价值的替代品）来质疑这两种不同异染色质构象的生物学相关性和功能相互作用。我们建立了 H3K27me3 和 H3K9me3 修饰的全基因组模式，并发现这些标记在基因丰富区域内相互排斥，但在重复区域内则不然。我们生成了相应的组蛋白甲基转移酶无效突变体，并显示了 H3K9me3 和 H3K27me3 标记的相互依赖性。事实上，去除 PaKmt6 EZH2 样酶不仅导致 H3K27me3 丢失，而且还导致 H3K9me3 显着减少。同样，去除 PaKmt1 SU(VAR)3-9 样酶会导致 H3K9me3 丢失和 H3K27me3 大幅减少。 H3K9me 结合蛋白 PaHP1 的去除进一步支持了每种类型的异染色质都需要另一种异染色质存在的观点。我们还确定 P. anserina 发育程序需要 H3K27me3 介导的沉默，因为 PaKmt6 EZH2 样酶的缺失会导致生命周期的大多数方面的严重缺陷，包括生长、分化过程和有性生殖，而 PaKmt1 SU 的缺失（ VAR)3-9 样酶仅导致边缘缺陷，类似于 PaHP1 的损失。我们的研究结果支持 PRC2 复合物在真菌发育中的保守功能。 然而，我们发现了抑制性组蛋白沉积机制中有趣的进化流动性，这挑战了组成型和兼性异染色质的规范定义。