YY1-dependent chromatin structure stabilization of B lineage commitment

在B细胞谱系定型过程中，基因在转录限制和转录调控之间的动态转移， 前原B细胞向原B细胞转变时的转录允许区室导致 B谱系程序和抑制替代谱系程序。虽然B血统的承诺是 通常认为是由谱系特异性转录因子驱动的，我们已经做出了令人惊讶的 发现普遍存在的转录因子YY 1的条件性敲除导致B谱系的丧失 这是由于细胞的定向分化，允许随后在体外和体内发育成T细胞谱系。先锋 转录因子如Ebf 1促进B谱系基因的转录并抑制 替代谱系基因启动B谱系承诺，但稳定的承诺需要改变， 前B细胞阶段的染色质结构。由于YY 1是控制谱系特异性基因的关键因子， 调控性长程染色质相互作用（LRCI），我们假设YY 1基因敲除前B细胞， 导致稳定维持B谱系特异性基因表达的染色质LRCI的丢失。一致 由此，我们发现YY 1敲除后B谱系转录物减少。YY 1也可以调解 Polycomb Group（PcG）抑制，我们发现YY 1敲除导致表达增加 的替代谱系基因，这表明YY 1的损失废除抑制染色质结构 来阻止这些基因的表达。因此，我们假设YY 1基因敲除前B细胞 导致稳定维持谱系特异性基因表达的染色质结构丢失， 抑制性染色质结构需要防止替代谱系基因表达，从而导致 失去了B血统的承诺。为了验证这一点，我们将确定染色质折叠模式，核 野生型和YY 1-null中关键基因、染色质可及性和表观遗传结构的定位 前B细胞，以确定在B谱系定型过程中由YY 1调节的基因组结构。到 确定YY 1的类似作用是否在T谱系中起作用，我们将确定YY 1缺失是否 促进YY 1-null DN 3细胞的谱系可塑性。YY 1在前B细胞中也是Igk位点所必需的 收缩所需的远端Vk基因重排。有人认为YY 1扮演了一个 在调节染色质结构中的结构作用，但尚不清楚这是否需要YY 1转录 激活、PcG或自关联功能。我们将利用一组已建立的YY 1突变体， 在这些功能中受到损害，以并行评估，YY 1调节的机制， B谱系定型所需的染色质结构，以及Igk基因座收缩和 Jk-Vk重排由于YY 1参与胚胎发生和多种组织类型的发育， 确定YY 1如何控制基因组结构以指定B谱系定型将提供一个新的 一个普遍存在的因素在谱系特异性发展的功能的范例。

During B cell lineage commitment, a dynamic shift of genes between transcriptionally restricted and transcriptionally permissive compartments at the pre-pro-B to pro-B cell transition results in activation of the B lineage program and repression of alternative lineage programs. While B lineage commitment is generally believed to be driven by lineage-specific transcription factors, we have made the surprising discovery that conditional knock-out of the ubiquitous transcription factor YY1 results in loss of B lineage commitment, allowing subsequent development into the T cell lineage both in vitro and in vivo. Pioneer transcription factors such as Ebf1 promote transcription of B lineages genes and repress expression of alternative lineage genes to initiate B lineage commitment, but stable commitment requires changes in chromatin structures at the pro-B cell stage. As YY1 is a key factor controlling lineage-specific gene regulatory long-range chromatin interactions (LRCIs), we hypothesize that YY1 knock-out in pro-B cells results in loss of chromatin LRCIs that stably maintain B lineage-specific gene expression. Consistent with this, we found reduction of B lineage transcripts after YY1 knock-out. YY1 can also mediate Polycomb Group (PcG) repression, and we found that YY1 knock-out resulted in increased expression of alternative lineage genes, suggesting that YY1 loss abrogates repressive chromatin structures needed to prevent expression of these genes. Thus, we hypothesize that YY1 knock-out in pro-B cells results in lost chromatin structures that stably maintain lineage-specific gene expression, as well as loss of repressive chromatin structures needed to prevent alternative lineage gene expression, thus leading to lost B lineage commitment. To test this, we will determine chromatin folding patterns, nuclear localization of key genes, chromatin accessibility, and epigenetic structures in wild-type and YY1-null pro-B cells to define the genomic structures regulated by YY1 during B lineage commitment. To determine if analogous effects of YY1 are operative in the T lineage, we will determine if YY1 loss promotes lineage plasticity of YY1-null DN3 cells. YY1 is also necessary in pro-B cells for Igk locus contraction required for rearrangement of distal Vk genes. It has been suggested that YY1 plays a structural role in regulating chromatin structures, but it is unclear if this requires the YY1 transcriptional activation, PcG, or self-association functions. We will utilize an established panel of YY1 mutants that are compromised in these functions to assess in parallel, the mechanisms of YY1 regulation of chromatin structures needed for B lineage commitment, and those needed for Igk locus contraction and Jk-Vk rearrangement. As YY1 is involved in embryogenesis and development of multiple tissue types, determining how YY1 controls genomic structures to specify B lineage commitment will provide a new paradigm for the function of a ubiquitous factor in lineage-specific development.