Parasitic trypanosomatids and phototrophic euglenids are among the most extensively studied euglenozoans. The phototrophic euglenid lineage arose relatively recently through secondary endosymbiosis between a phagotrophic euglenid and a prasinophyte green alga that evolved into the euglenid secondary chloroplast. The parasitic trypanosomatids (i.e. Trypanosoma spp. and Leishmania spp.) and the freshwater phototrophic euglenids (i.e. Euglena gracilis) are the most evolutionary distant lineages in the Euglenozoa phylogenetic tree. The molecular and cell biological traits they share can thus be considered as ancestral traits originating in the common euglenozoan ancestor. These euglenozoan ancestral traits include common mitochondrial presequence motifs, respiratory chain complexes containing various unique subunits, a unique ATP synthase structure, the absence of mitochondria‐encoded transfer RNAs (tRNAs), a nucleus with a centrally positioned nucleolus, closed mitosis without dissolution of the nuclear membrane and nucleoli, a nuclear genome containing the unusual ‘J’ base (β‐D‐glucosyl‐hydroxymethyluracil), processing of nucleus‐encoded precursor messenger RNAs (pre‐mRNAs) via spliced‐leader RNA (SL‐RNA) trans‐splicing, post‐transcriptional gene silencing by the RNA interference (RNAi) pathway and the absence of transcriptional regulation of nuclear gene expression. Mitochondrial uridine insertion/deletion RNA editing directed by guide RNAs (gRNAs) evolved in the ancestor of the kinetoplastid lineage. The evolutionary origin of other molecular features known to be present only in either kinetoplastids (i.e. polycistronic transcripts, compaction of nuclear genomes) or euglenids (i.e. monocistronic transcripts, huge genomes, many nuclear cis‐spliced introns, polyproteins) is unclear.

中文翻译：

---

光养眼虫和寄生锥虫的比较分子细胞生物学揭示了眼虫的祖先

寄生锥虫和光养眼虫是研究最广泛的眼虫。光养眼线虫谱系是最近通过吞噬眼线虫和进化为眼线虫次生叶绿体的草本绿藻之间的二次内共生而出现的。寄生性锥虫（即锥虫属和利什曼原虫）和淡水光养眼虫（即 Euglena gracilis）是眼虫系统发育树中进化最远的谱系。因此，它们共享的分子和细胞生物学特征可以被认为是源自共同裸眼动物祖先的祖先特征。这些裸眼动物祖先特征包括常见的线粒体前序基序、包含各种独特亚基的呼吸链复合物、独特的 ATP 合酶结构、没有线粒体编码的转移 RNA (tRNA)，核仁位于中央，有丝分裂闭合，核膜和核仁不溶解，核基因组包含不寻常的“J”碱基（β-D-葡萄糖基-羟甲基尿嘧啶） , 通过剪接前导 RNA (SL-RNA) 反式剪接处理核编码的前体信使 RNA (pre-mRNAs)，通过 RNA 干扰 (RNAi) 途径进行转录后基因沉默和缺乏核基因的转录调控表达。由引导 RNA (gRNA) 指导的线粒体尿苷插入/缺失 RNA 编辑在动质体谱系的祖先中进化。已知仅存在于动质体（即多顺反子转录本、核基因组的压缩）或眼虫（即