Department of Biology, Dalhousie University, Halifax, NS B3H 4R2, Canada.
Protist. 2013 Sep;164(5):598-621. doi: 10.1016/j.protis.2013.05.005. Epub 2013 Jul 18.
Apusomonads are of evolutionary interest because they are close relatives to the supergroup Opisthokonta, which contains both animals and fungi. There are no detailed morphological studies of 'amastigomonad' type apusomonads, such as Thecamonas trahens, despite this species having a sequenced genome. We use serial-section transmission electron microscopy and 3D reconstruction to examine the cell architecture and complete microtubular cytoskeleton of Thecamonas. Thecamonas has two flagella and an anteriorly projecting 'tusk'. The anterior basal body associates with one microtubular root, which travels leftward, and a non-root 'ribbon' of six microtubules that travels down the right side of the cell. The posterior basal body associates with three roots: an eight-membered right root, a doublet left root, and an intermediate singlet root. These rearrange into two bands, both on the left side of the cell. One comprises the left and singlet roots plus one right root microtubule. The other comprises the remaining right root microtubules. A splitting right root and supernumerary singlet root are also present in breviates, ancyromonads, and 'typical excavates', suggesting that these characters are ancestral for much of eukaryote diversity. If so, opisthokonts, and most or all living eukaryotes, probably arose from cells with complex microtubular cytoskeletons.
锥体虫是进化研究的对象，因为它们是后生动物超群的近亲，后生动物超群包含动物和真菌。尽管 Thecamonas trahens 这种物种有测序的基因组，但对“动基体亚目锥体虫”类型的锥体虫没有详细的形态学研究。我们使用连续切片透射电子显微镜和 3D 重建来研究 Thecamonas 的细胞结构和完整的微管细胞骨架。Thecamonas 有两个鞭毛和一个向前突出的“獠牙”。前基体与一个向左行进的微管根以及一个由六根微管组成的非根“带”相连，该带沿细胞右侧向下行进。后基体与三个根相连：一个由八个成员组成的右根、一个双联体左根和一个中间的单根。这些根重新排列成两条带，都位于细胞的左侧。一个由左根和单根以及一个右根微管组成。另一个由其余的右根微管组成。在短体虫、动基体类和“典型挖掘虫”中也存在分裂的右根和额外的单根，这表明这些特征是大多数真核生物多样性的祖先特征。如果是这样，后生动物超群，以及大多数或所有现存的真核生物，可能是由具有复杂微管细胞骨架的细胞产生的。
