The Sexual Ancestor of all Eukaryotes: A Defense of the “Meiosis Toolkit”

Abstract

The distribution pattern of the meiotic machinery in known eukaryotes is most parsimoniously explained by the hypothesis that all eukaryotes are ancestrally sexual. However, this assumption is questioned by preliminary results, in culture conditions. These suggested that Acanthamoeba, an organism considered to be largely asexual, constitutively expresses meiosis genes nevertheless—at least in the lab. This apparent disconnect between the “meiosis toolkit” and sexual processes in Acanthamoeba led to the conclusion that the eukaryotic ancestor is asexual. In this review, the “meiosis toolkit” is rigorously defended, drawing on numerous research articles. Additionally, the claim of constitutive meiotic gene expression is probed in Acanthamoeba via the same transcriptomics data. The results show that the expression of the meiotic machinery is not constitutive in Acanthamoeba as claimed before. Furthermore, it is argued that this would have no implications for understanding the nature of the eukaryotic ancestor, regardless of the result.

Chromosome-scale assembly of the streamlined picoeukaryote Picochlorum sp. SENEW3 genome reveals Rabl-like chromatin structure and potential for C4 photosynthesis

“…Meiosis is a key process in evolutionary diversification in eukaryotic organisms, however in several groups of green algae, sexual reproduction is either absent or yet undocumented, as appears to be the case for most planktonic species [1,113]. The presence of core meiotic determinant genes (though many more are involved in the process) [114,115] was examined to assess whether P. SENEW3 is likely to undertake sexual reproduction. Several of these were identified: DMC1, HOP2, MSH5 (and homologues MSH2 and MSH6) SPO11-2, HAP2 and MER3; yet six others were missing (Table S13), suggesting but leaving uncertain whether P. SENEW3 can undergo meiosis.…”

Leishmania 360°: Guidelines for Exosomal Research

“…At present, caution is required defining cell types based solely on their morphology, given that few molecular markers are available to identify life cycle forms [35,38,46,47]. The shape and configuration of the Leishmania cell are nevertheless linked intimately with the pathogenicity and ecological niche of the species, and must be transmitted accurately from one generation to the next during mitotic division, although recent studies have shown meiosis-like sexual recombination in Leishmania, and other sexual processes may be possible [22,41,[48][49][50]. Both forms of development conserve their basic cell architecture and ultrastructural features over the course of the life cycle, with the kinetoplast anterior to the nucleus [44,45,47,49,50].…”

“…The shape and configuration of the Leishmania cell are nevertheless linked intimately with the pathogenicity and ecological niche of the species, and must be transmitted accurately from one generation to the next during mitotic division, although recent studies have shown meiosis-like sexual recombination in Leishmania, and other sexual processes may be possible [22,41,[48][49][50]. Both forms of development conserve their basic cell architecture and ultrastructural features over the course of the life cycle, with the kinetoplast anterior to the nucleus [44,45,47,49,50]. In these cells, much of the single, branched mitochondrion contains kinetoplast DNA (kDNA) that is connected to the basal body, where a single flagellum extends from the flagellar pocket (FP), to which it is attached by a cytoskeletal structure called the Flagellum Attachment Zone (FAZ) (Figure 3) [40,41,[44][45][46].…”

Genome basis for functional differentiation in uncultured lineages of marine bacterivores

“…Moreover, genomic approaches proved to be powerful for identifying other specific eukaryotic features such as meiosis (a stage of sexual reproduction), which evolved early in eukaryotes (Speijer et al 2015) and for which a full set of responsible genes was proposed, mostly defined from Opistokonta and plants. Using the proposed meiosistoolkit, it has been possible to perform large-scale comparative analysis and search for these genes in other protists like diatoms (Ramesh et al 2005, Malik et al 2008, Patil et al 2015, Hofstatter et al 2020. Similarly, genomics supported the discovery of flagellum specific proteins (flagellum toolkit) in Opistokonta (Torruella et al 2015) or Fungi , helping to elucidate the evolutionary history of this ancestral feature specific of a given lifestyle.…”