Abstract:
Transcription control is a major determinant of cell fate decisions in somatic tissues. By contrast, early germline fate specification in numerous vertebrate and invertebrate species relies extensively on RNA-level regulation, exerted on asymmetrically inherited maternal supplies, with little-to-no zygotic transcription. However delayed, a maternal-to-zygotic transition is nevertheless poised to complete the deployment of pre-gametic programs in the germline. Here, we focus on early germline specification in the tunicate Ciona to study zygotic genome activation. We first demonstrate that a peculiar cellular remodeling event excludes localized postplasmic Pem-1 mRNA, which encodes the general inhibitor of transcription. Subsequently, zygotic transcription begins in Pem-1-negative primordial germ cells (PGCs), as revealed by histochemical detection of elongating RNA Polymerase II, and nascent Mef2 transcripts. In addition, we uncover a provisional antagonism between JAK and MEK/BMPRI/GSK3 signaling, which controls the onset of zygotic gene expression, following cellular remodeling of PGCs. We propose a 2-step model for the onset of zygotic transcription in the Ciona germline and discuss the significance of germ plasm dislocation and remodeling in the context of developmental fate specification.
摘要:
转录控制是体细胞组织中细胞命运决定的主要决定因素。相比之下,许多脊椎动物和无脊椎动物物种的早期种系命运规范广泛依赖于RNA水平的调节,施加于不对称遗传的母体供应,几乎没有合子转录。然而延迟,然而,从母体到合子的过渡已准备好完成种系中配子前计划的部署.这里,我们专注于被膜Ciona的早期种系规范,以研究合子基因组的激活。我们首先证明了一个特殊的细胞重塑事件排除了局部的后质Pem-1mRNA,它编码转录的一般抑制剂。随后,合子转录始于Pem-1阴性原始生殖细胞(PGCs),如延伸RNA聚合酶II的组织化学检测所示,和新生的Mef2成绩单。此外,我们发现JAK和MEK/BMPRI/GSK3信号之间的暂时拮抗作用,控制合子基因表达的开始,PGCs细胞重塑后。我们提出了Ciona种系中合子转录开始的两步模型,并讨论了在发育命运规范的背景下种质错位和重塑的重要性。