Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada.
Genome Biol Evol. 2019 Mar 1;11(3):678-687. doi: 10.1093/gbe/evz029.
The nuclear pore complex (NPC) is a large macromolecular assembly situated within the pores of the nuclear envelope. Through interactions between its subcomplexes and import proteins, the NPC mediates the transport of molecules into and out of the nucleus and facilitates dynamic chromatin regulation and gene expression. Accordingly, the NPC constitutes a highly integrated nuclear component that is ubiquitous and conserved among eukaryotes. Potential exceptions to this are nucleomorphs: Highly reduced, relict nuclei that were derived from green and red algae following their endosymbiotic integration into two lineages, the chlorarachniophytes and the cryptophyceans. A previous investigation failed to identify NPC genes in nucleomorph genomes suggesting that these genes have either been relocated to the host nucleus or lost. Here, we sought to investigate the composition of the NPC in nucleomorphs by using genomic and transcriptomic data to identify and phylogenetically classify NPC proteins in nucleomorph-containing algae. Although we found NPC proteins in all examined lineages, most of those found in chlorarachniophytes and cryptophyceans were single copy, host-related proteins that lacked signal peptides. Two exceptions were Nup98 and Rae1, which had clear nucleomorph-derived homologs. However, these proteins alone are likely insufficient to structure a canonical NPC and previous reports revealed that Nup98 and Rae1 have other nuclear functions. Ultimately, these data indicate that nucleomorphs represent eukaryotic nuclei without a canonical NPC, raising fundamental questions about their structure and function.
核孔复合体（NPC）是位于核膜孔内的大型大分子组装体。通过其亚基和输入蛋白之间的相互作用，NPC 介导分子进出细胞核的运输，并促进动态染色质调节和基因表达。因此，NPC 构成了一个高度整合的核成分，在真核生物中普遍存在且保守。这种情况的潜在例外是核质体：高度简化的遗留核，这些核是由绿藻和红藻在其内共生整合到两个谱系（chlorarachniophytes 和 cryptophyceans）后衍生而来的。先前的研究未能在核质体基因组中鉴定出 NPC 基因，这表明这些基因要么已经被转移到宿主核中，要么已经丢失。在这里，我们试图通过使用基因组和转录组数据来鉴定和系统发育分类核质体藻类中的 NPC 蛋白，从而研究核质体中的 NPC 组成。尽管我们在所有检查的谱系中都发现了 NPC 蛋白，但在 chlorarachniophytes 和 cryptophyceans 中发现的大多数蛋白都是缺乏信号肽的单一拷贝的宿主相关蛋白。两个例外是 Nup98 和 Rae1，它们有明显的核质体衍生同源物。然而，这些蛋白本身可能不足以构建一个典型的 NPC，并且先前的报告表明 Nup98 和 Rae1 具有其他核功能。最终，这些数据表明核质体代表没有典型 NPC 的真核核，这引发了关于它们的结构和功能的基本问题。
