Distinct functions of polycomb group proteins in regulating Ci transcription in developing Drosophila.
Distinct functions of polycomb group proteins in regulating Ci transcription in developing Drosophila.
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DOI：
10.1093/jmcb/mjy009
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发表时间：
2018-10
影响因子：
5.5
通讯作者：
Xiangdong Lv;Hao Chen;Shuo Zhang;Zhao Zhang;Chenyu Pan;Yuanxin Xia;Jialin Fan;Wenqing Wu
中科院分区：
文献类型：
--
作者：
Xiangdong Lv;Hao Chen;Shuo Zhang;Zhao Zhang;Chenyu Pan;Yuanxin Xia;Jialin Fan;Wenqing Wu
尊敬的编辑，高度保守的polycomb group（PcG）蛋白最初在果蝇中被鉴定为维持同源异型基因转录的抑制状态，这对动物发育控制至关重要（Sawarkar and Paro，2010）。多梳阻遏复合物1（PRC 1）和2（PRC 2）是PcG蛋白的两种重要的多蛋白复合物，调节靶基因的表达。在果蝇中，PRC 2由zeste增强子（E（z））、zeste抑制子12（Su（z）12）、额外性梳（esc）和染色质组装因子1亚基（Caf 1）组成。E（z）是H3 K27 me 2/3的催化亚基，而Su（z）12和Ec都是体内适当催化活性所需的（Helin和Morey，2010）。PRC 1包含四种蛋白质的核心：Polycomb（Pc）、Polyhomeotic（Ph）、Sex combs extra（Sce）和Posterior sex combs（Psc）。通过其染色体结构域，Pc可以特异性识别H3 K27 me 3，并将其他组分募集到选定的染色质位点（Beisel和Paro，2011），尽管也有报道称PRC 1的H3 K27 me 3非依赖性募集。PRC 1可以通过催化H2 A单泛素化（Wang et al.，2004）或诱导局部染色质凝聚（Escherichandetal.，2010年）。大多数文献表明PcG蛋白在基因转录调控中起抑制作用。最近，我们和其他人发现PcG也可能在某些基因的转录中起正调节剂的作用（Lv等人，2016年）。不同的PcG蛋白可能在正或负转录调控中具有不同的功能。同时，我们鉴定了来自PRC 1的Pc和Sce可以正调控中断肘（C1）的转录，中断肘（C1）是对动物发育和成体干细胞维持至关重要的Hedgehog（Hh）信号传导途径的效应子（图1A-C '）（Lv等人，2018年）。因此，以Ci为例来阐明不同PcG蛋白在正常发育过程中促进转录的作用是有趣的。类似于在Pc或Sce突变克隆中观察到的表型（Lv等人，2018），特异性地敲低GFP阳性区域中的Pc或Sce显著降低Ci水平，而去抑制超双胸（Ubx）表达（图1A-C '），这是一种被PcG抑制的众所周知的经典PcG靶标（Sawarkar和Paro，2010）。然后，我们测试了PRC 1的其他组分Ph和Psc在Ci转录调节中的功能，因为据报道Ph抑制Ci表达（Randsholt等人，2000年）。与我们在Pc-Sce敲低克隆中显示Ci表达显著降低的发现不同（图1A-C '），我们在Ph和Psc-Su（z）2 RNAi克隆中均未观察到对Ci水平的明显抑制（图1D-E'）。因此，经典PRC 1的亚复合物概念正在出现，这与先前的报告一致，该报告表明Pc和Sce具有更相似的功能，而Ph和Psc更相似（Gutierrez等人，2012年）。由于以往的研究已经证明Pc可以通过其chromodomain特异性识别PRC 2催化的H3 K27 me 3，我们开始探索chromodomain是否是Pc介导的Ci转录所必需的。我们采用了Pc突变体Pc Δ69-70，其在Ile 69和Asp 70处具有缺失，导致Pc的染色体结构域功能被破坏并消除了Pc的染色体结合能力（Fischle等人，2003年）。WT Pc的过表达（PcWT）对细胞凋亡水平无影响。
Dear Editor, The highly conserved polycomb group (PcG) proteins were initially identified in Drosophila to maintain repression state of the transcription of homeotic genes, which is critical for animal development control (Sawarkar and Paro, 2010). Polycomb repressive complexes 1 (PRC1) and 2 (PRC2) are two important multi-protein complexes of PcG proteins regulating target gene expression. In Drosophila, PRC2 is composed of Enhancer of zeste (E (z)), Suppressor of zeste 12 (Su (z) 12), Extra sex combs (esc), and Chromatin assembly factor 1 subunit (Caf1). E (z) is the catalytic subunit for H3K27me2/3, while both Su (z) 12 and Esc are required for the proper catalytic activity in vivo (Helin and Morey, 2010). PRC1 contains a core of four proteins: Polycomb (Pc), Polyhomeotic (Ph), Sex combs extra (Sce), and Posterior sex combs (Psc). Through its chromodomain, Pc can specifically recognize H3K27me3, and recruit other components to selected chromatin sites (Beisel and Paro, 2011), although H3K27me3-independent recruitment of PRC1 has also been reported. PRC1 can repress its targets by either catalyzing H2A mono-ubiquitination (Wang et al., 2004) or inducing local chromatin condensation (Eskeland et al., 2010). Majority of the documents indicate that PcG proteins play repressive roles in gene transcriptional regulation. Recently, we and others identified that PcGs might also function as a positive regulator in the transcription of certain genes (Lv et al., 2016). It is likely that different PcG proteins have different functions in positive or negative transcriptional regulation. Meanwhile, we identified that Pc and Sce from PRC1 can positively regulate transcription of cubitus interruptus (Ci), the effector of the Hedgehog (Hh) signaling pathway critical for animal development and adult stem cell maintenance (Figure 1 A–C’)(Lv et al., 2018). It is, therefore, interesting to take Ci as an example to clarify the role of different PcG proteins in promoting transcription during normal developmental process. Similar with the phenotype observed in Pc or Sce mutant clones (Lv et al., 2018), knocking down of Pc or Sce specifically in GFP-positive region dramatically decreased the Ci level whereas derepressed the Ultrabithorax (Ubx) expression (Figure 1 A–C’), a well-known classical PcGs target repressed by PcGs (Sawarkar and Paro, 2010). We then tested the function of other components of PRC1, Ph and Psc, in Ci transcriptional regulation, since Ph has been reported to repress Ci expression (Randsholt et al., 2000). Different from our findings in Pc-Sce knockdown clones showing a significant decrease in Ci expression (Figure 1 A–C’), we did not observe obvious repression on Ci levels in both Ph and Psc-Su (z) 2 RNAi clones (Figure 1 D–E’). Thus, the subcomplex concept of classical PRC1 is emerging, which is consistent with a previous report suggesting that Pc and Sce have more similar function whereas Ph and Psc are more similar (Gutierrez et al., 2012). Since previous studies have demonstrated that Pc can specifically recognize H3K27me3 catalyzed by PRC2 via its chromodomain, we started to explore whether the chromodomain is required for Pcmediated Ci transcription. We adopted a Pc mutant, Pc Δ69–70, which harbors a deletion at Ile69 and Asp70, resulting in disrupted chromodomain function and abolished chromosome binding capacity of Pc (Fischle et al., 2003). Overexpression of WT Pc (PcWT) had no effect on the level