Islas-Morales Parsifal F, Cárdenas Anny, Mosqueira María J, Jiménez-García Luis Felipe, Voolstra Christian R
Programa de Doctorado en Ciencias Biomédicas, Facultad de Medicina, UNAM, Mexico City, Mexico.
UNESCO Chair on Science Diplomacy and Scientific Heritage, Instituto de Biología, UNAM, Mexico City, Mexico.
Front Microbiol. 2023 Feb 2;14:1075071. doi: 10.3389/fmicb.2023.1075071. eCollection 2023.
Nucleoli are subcellular compartments where transcription and maturation of pre-ribosomal RNAs occur. While the transcription of ribosomal RNAs is common to all living cells, the presence and ultrastructure of nucleoli has been only documented in eukaryotes. Asgard-Archaea, the closest prokaryotic relatives of eukaryotes, and their near relatives TACK-Archaea have homologs of nucleolar proteins and RNAs in their genome, but the cellular organization of both is largely unexplored. Here we provide ultrastructural and molecular evidence for the presence of putative nucleolus-like subcellular domains in the TACK crenarchaeon (formerly known as ). Transmission electron microscopy (TEM) revealed consistent electron-dense fibro-granular compartments, also positive to the specific silver staining for nucleolar organizer regions (AgNOR). TEM also confirmed that ribosomal DNA (rDNA) is spatially distributed in non-random, clustered arrays underlying fine structures, as observed by ultrastructural hybridization (UISH). To further explore these observations, proteomic sequencing of isolated bands from AgNOR-stained protein gels was conducted and compared against a compiled inventory of putative nucleolar homologs from the P1 genome. Sequenced AgNOR-sensitive peptides encoded homologs of eukaryotic nucleoli proteins, enriched for nucleolus-related functions. Our results provide first evidence that subcellular domains of nucleolar-like nature are not exclusive to eukaryotes. Based on our data, we propose a model for a putative nucleolus in . Whereas technical limitations and further aspects remain a matter for future functional studies, our data supports the origin of nucleoli within the common ancestor of Eukarya and TACK-Archaea, based on a two-domain tree of life.
核仁是核糖体前体RNA转录和成熟的亚细胞区室。虽然核糖体RNA的转录在所有活细胞中都很常见，但核仁的存在和超微结构仅在真核生物中有记录。阿斯加德古菌是真核生物最接近的原核生物亲属，它们的近缘亲属泉古菌门在其基因组中具有核仁蛋白和RNA的同源物，但两者的细胞组织在很大程度上尚未被探索。在这里，我们提供了超微结构和分子证据，证明在泉古菌门（以前称为 ）中存在假定的核仁样亚细胞结构域。透射电子显微镜（TEM）显示出一致的电子致密纤维颗粒区室，对核仁组织区的特异性银染（AgNOR）也呈阳性。TEM还证实，核糖体DNA（rDNA）在超微结构杂交（UISH）观察到的精细结构下以非随机的、成簇的阵列形式在空间上分布。为了进一步探究这些观察结果，我们对AgNOR染色的蛋白质凝胶分离条带进行了蛋白质组测序，并与来自 P1基因组的假定核仁同源物汇编清单进行了比较。测序的AgNOR敏感肽编码真核核仁蛋白的同源物，富集了与核仁相关的功能。我们的结果首次证明，类似核仁性质的亚细胞结构域并非真核生物所特有。基于我们的数据，我们提出了一个关于 中假定核仁的模型。虽然技术限制和其他方面仍然是未来功能研究的问题，但我们的数据支持基于两域生命树的核仁起源于真核生物和泉古菌门的共同祖先。
