Laboratory of Silkworm Science, Kyushu University Graduate School of Bioresource and Bioenvironmental Sciences, Fukuoka, Japan.
PLoS One. 2012;7(4):e34330. doi: 10.1371/journal.pone.0034330. Epub 2012 Apr 2.
Polycomb group (PcG) proteins are evolutionarily conserved chromatin modifiers and act together in three multimeric complexes, Polycomb repressive complex 1 (PRC1), Polycomb repressive complex 2 (PRC2), and Pleiohomeotic repressive complex (PhoRC), to repress transcription of the target genes. Here, we identified Polycomb target genes in Bombyx mori with holocentric centromere using genome-wide expression screening based on the knockdown of BmSCE, BmESC, BmPHO, or BmSCM gene, which represent the distinct complexes. As a result, the expressions of 29 genes were up-regulated after knocking down 4 PcG genes. Particularly, there is a significant overlap between targets of BmPho (331 out of 524) and BmScm (331 out of 532), and among these, 190 genes function as regulator factors playing important roles in development. We also found that BmPho, as well as BmScm, can interact with other Polycomb components examined in this study. Further detailed analysis revealed that the C-terminus of BmPho containing zinc finger domain is involved in the interaction between BmPho and BmScm. Moreover, the zinc finger domain in BmPho contributes to its inhibitory function and ectopic overexpression of BmScm is able to promote transcriptional repression by Gal4-Pho fusions including BmScm-interacting domain. Loss of BmPho expression causes relocalization of BmScm into the cytoplasm. Collectively, we provide evidence of a functional link between BmPho and BmScm, and propose two Polycomb-related repression mechanisms requiring only BmPho associated with BmScm or a whole set of PcG complexes.
多梳组（PcG）蛋白是进化上保守的染色质修饰物，它们共同作用于三个多聚体复合物中，即多梳抑制复合物 1（PRC1）、多梳抑制复合物 2（PRC2）和 Pleiohomeotic 抑制复合物（PhoRC），以抑制靶基因的转录。在这里，我们使用基于 BmSCE、BmESC、BmPHO 或 BmSCM 基因敲低的全基因组表达筛选，在具有着丝粒的家蚕中鉴定了 Polycomb 靶基因。结果，敲低 4 个 PcG 基因后，有 29 个基因的表达上调。特别是，BmPho（524 个中有 331 个）和 BmScm（532 个中有 331 个）的靶基因之间存在显著重叠，其中 190 个基因作为调节因子发挥重要作用在发育中。我们还发现 BmPho 以及 BmScm 可以与本研究中检查的其他 Polycomb 成分相互作用。进一步的详细分析表明，BmPho 的 C 端包含锌指结构域，参与了 BmPho 和 BmScm 之间的相互作用。此外，BmPho 中的锌指结构域有助于其抑制功能，过表达 BmScm 能够促进 Gal4-Pho 融合体的转录抑制，包括 BmScm 相互作用结构域。BmPho 表达的缺失导致 BmScm 重新定位到细胞质中。总之，我们提供了 BmPho 和 BmScm 之间存在功能联系的证据，并提出了两种仅需要 BmPho 与 BmScm 相关或整个 PcG 复合物的 Polycomb 相关抑制机制。
