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Naegleria's mitotic spindles are built from unique tubulins and highlight core spindle features.

ABSTRACT: Naegleria gruberi is a unicellular eukaryote whose evolutionary distance from animals and fungi has made it useful for developing hypotheses about the last common eukaryotic ancestor. Naegleria amoebae lack a cytoplasmic microtubule cytoskeleton and assemble microtubules only during mitosis and thus represent a unique system for studying the evolution and functional specificity of mitotic tubulins and the spindles they assemble. Previous studies show that Naegleria amoebae express a divergent α-tubulin during mitosis, and we now show that Naegleria amoebae express a second mitotic α- and two mitotic β-tubulins. The mitotic tubulins are evolutionarily divergent relative to typical α- and β-tubulins and contain residues that suggest distinct microtubule properties. These distinct residues are conserved in mitotic tubulin homologs of the "brain-eating amoeba" Naegleria fowleri, making them potential drug targets. Using quantitative light microscopy, we find that Naegleria's mitotic spindle is a distinctive barrel-like structure built from a ring of microtubule bundles. Similar to those of other species, Naegleria's spindle is twisted, and its length increases during mitosis, suggesting that these aspects of mitosis are ancestral features. Because bundle numbers change during metaphase, we hypothesize that the initial bundles represent kinetochore fibers and secondary bundles function as bridging fibers.

SUBMITTER: Velle KB

PROVIDER: S-EPMC9036621 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND:Polyploidy has long been recognized as playing an important role in plant evolution. In flowering plants, the major route of polyploidization is suggested to be sexual through gametes with somatic chromosome number (2n). Parallel Spindle1 gene in Arabidopsis thaliana (AtPS1) was recently demonstrated to control spindle orientation in the 2nd division of meiosis and, when mutated, to induce 2n pollen. Interestingly, AtPS1 encodes a protein with a FHA domain and PINc domain putatively involved in RNA decay (i.e. Nonsense Mediated mRNA Decay). In potato, 2n pollen depending on parallel spindles was described long time ago but the responsible gene has never been isolated. The knowledge derived from AtPS1 as well as the availability of genome sequences makes it possible to isolate potato PSLike (PSL) and to highlight the evolution of PSL family in plants. RESULTS:Our work leading to the first characterization of PSLs in potato showed a greater PSL complexity in this species respect to Arabidopsis thaliana. Indeed, a genomic PSL locus and seven cDNAs affected by alternative splicing have been cloned. In addition, the occurrence of at least two other PSL loci in potato was suggested by the sequence comparison of alternatively spliced transcripts.Phylogenetic analysis on 20 Viridaeplantae showed the wide distribution of PSLs throughout the species and the occurrence of multiple copies only in potato and soybean.The analysis of PSLFHA and PSLPINc domains evidenced that, in terms of secondary structure, a major degree of variability occurred in PINc domain respect to FHA. In terms of specific active sites, both domains showed diversification among plant species that could be related to a functional diversification among PSL genes. In addition, some specific active sites were strongly conserved among plants as supported by sequence alignment and by evidence of negative selection evaluated as difference between non-synonymous and synonymous mutations. CONCLUSIONS:In this study, we highlight the existence of PSLs throughout Viridaeplantae, from mosses to higher plants. We provide evidence that PSLs occur mostly as singleton in the analyzed genomes except in soybean and potato both characterized by a recent whole genome duplication event. In potato, we suggest the candidate PSL gene having a role in 2n pollen that should be deeply investigated.We provide useful insight into evolutionary conservation of FHA and PINc domains throughout plant PSLs which suggest a fundamental role of these domains for PSL function.

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Naegleria's mitotic spindles are built from unique tubulins and highlight core spindle features.

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