Pioneer and nonpioneer factor cooperation drives lineage specific chromatin opening [scRNA-seq]

Pioneer transcription factors are coined as having the unique property of "opening closed chromatin sites" for implementation of cell fates. We previously showed that the pioneer Pax7 specifies melanotrope cells through deployment of an enhancer repertoire: this allows binding of Tpit, a nonpioneer factor that determines the related lineages of melanotropes and corticotropes. Here, we investigated the relation between these two factors in the pioneer mechanism. Cell-specific gene expression and chromatin landscapes were defined by scRNAseq and chromatin accessibility profiling. We found that in vivo deployment of the melanotrope enhancer repertoire and chromatin opening requires both Pax7 and Tpit. In cells, binding of heterochromatin targets by Pax7 is independent of Tpit but Pax7-dependent chromatin opening requires Tpit. The present work shows that pioneer core properties are limited to the ability to recognize heterochromatin targets and facilitate nonpioneer binding. Chromatin opening per se may be provided through cooperation with nonpioneer factors. Single cell RNAseq of adult male mouse pituitary先驱转录因子（Pioneer transcription factors）被定义为具有"打开封闭染色质位点"的独特特性，以介导细胞命运的确立。本团队此前的研究表明，先驱转录因子PAX7可通过激活一套增强子组库，定向分化促黑素细胞：该增强子组库可允许TPIT结合——TPIT是一种非先驱转录因子，负责调控促黑素细胞与促肾上腺皮质激素细胞的相关细胞谱系。本研究旨在探究这两种因子在先驱转录机制中的相互关系。研究通过单细胞RNA测序（scRNAseq）与染色质可及性谱分析，明确了细胞特异性基因表达特征与染色质开放性景观。我们发现，体内激活促黑素细胞的增强子组库以及染色质开放过程，同时依赖PAX7与TPIT。在细胞中，PAX7结合异染色质靶位点的过程不依赖TPIT，但PAX7介导的染色质开放则需要TPIT的参与。本研究表明，先驱转录因子的核心特性仅局限于识别异染色质靶位点，并促进非先驱转录因子的结合。而染色质开放本身，则可通过与非先驱转录因子的协同作用实现。成年雄性小鼠垂体的单细胞RNA测序