Institute for Molecular Evolution, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.
Genome Biol Evol. 2023 Mar 3;15(3). doi: 10.1093/gbe/evad016.
All eukaryotes have linear chromosomes that are distributed to daughter nuclei during mitotic division, but the ancestral state of nuclear division in the last eukaryotic common ancestor (LECA) is so far unresolved. To address this issue, we have employed ancestral state reconstructions for mitotic states that can be found across the eukaryotic tree concerning the intactness of the nuclear envelope during mitosis (open or closed), the position of spindles (intranuclear or extranuclear), and the symmetry of spindles being either axial (orthomitosis) or bilateral (pleuromitosis). The data indicate that the LECA possessed closed orthomitosis with intranuclear spindles. Our reconstruction is compatible with recent findings indicating a syncytial state of the LECA, because it decouples three main processes: chromosome division, chromosome partitioning, and cell division (cytokinesis). The possession of closed mitosis using intranuclear spindles adds to the number of cellular traits that can now be attributed to LECA, providing insights into the lifestyle of this otherwise elusive biological entity at the origin of eukaryotic cells. Closed mitosis in a syncytial eukaryotic common ancestor would buffer mutations arising at the origin of mitotic division by allowing nuclei with viable chromosome sets to complement defective nuclei via mRNA in the cytosol.
所有真核生物的线性染色体都在有丝分裂过程中分配到子核中，但在最后一个真核生物共同祖先（LECA）中的核分裂的祖先状态至今仍未解决。为了解决这个问题，我们针对有丝分裂状态进行了祖先状态重建，可以在整个真核生物树中找到有丝分裂过程中核膜完整性（开放或关闭）、纺锤体位置（核内或核外）以及纺锤体对称性（轴向或双侧）的有丝分裂状态。数据表明，LECA 具有封闭的轴向有丝分裂，纺锤体位于核内。我们的重建与最近的发现一致，表明 LECA 处于合胞体状态，因为它分离了三个主要过程：染色体分裂、染色体分区和细胞分裂（胞质分裂）。使用核内纺锤体进行封闭的有丝分裂增加了现在可以归因于 LECA 的细胞特征数量，为了解真核细胞起源时这个难以捉摸的生物实体的生活方式提供了线索。合胞体真核生物共同祖先中的封闭有丝分裂可以通过允许具有可行染色体组的核通过细胞质中的 mRNA 来补充有缺陷的核，从而缓冲有丝分裂分裂起源处出现的突变。
