A Phylogenomic Inventory of Meiotic Genes

Department of Biology, Roanoke College, Salem, VA 24153, USA.
Current Biology (Impact Factor: 9.57). 02/2005; 15(2):185-91. DOI: 10.1016/j.cub.2005.01.003
Source: PubMed


Sexual reproduction in eukaryotes is accomplished by meiosis, a complex and specialized process of cell division that results in haploid cells (e.g., gametes). The stereotypical reductive division in meiosis is a major evolutionary innovation in eukaryotic cells, and delineating its history is key to understanding the evolution of sex. Meiosis arose early in eukaryotic evolution, but when and how meiosis arose and whether all eukaryotes have meiosis remain open questions. The known phylogenetic distribution of meiosis comprises plants, animals, fungi, and numerous protists. Diplomonads including Giardia intestinalis (syn. G. lamblia) are not known to have a sexual cycle; these protists may be an early-diverging lineage and could represent a premeiotic stage in eukaryotic evolution. We surveyed the ongoing G. intestinalis genome project data and have identified, verified, and analyzed a core set of putative meiotic genes-including five meiosis-specific genes-that are widely present among sexual eukaryotes. The presence of these genes indicates that: (1) Giardia is capable of meiosis and, thus, sexual reproduction, (2) the evolution of meiosis occurred early in eukaryotic evolution, and (3) the conserved meiotic machinery comprises a large set of genes that encode a variety of component proteins, including those involved in meiotic recombination.

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Available from: Banoo Malik
    • "This is the major pathway used by lower eukaryotes, including protozoan parasites, to repair double stranded DNA damages (Bhattacharyya et al., 2004). Putative meiosis genes were detected in the genome of G. intestinalis (Ramesh et al., 2005) but much remains to be studied about the mechanism of homologous recombination in this parasite. Further studies of the proteins listed in Table S5 might reveal how Giardia deals with DNA damage. "
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    ABSTRACT: The response to ultraviolet light (UV) radiation, a natural stressor to the intestinal protozoan parasite Giardia intestinalis, was studied to deepen the understanding of how the surrounding environment affects the parasite during transmission. UV radiation at 10 mJ/cm(2) kills Giardia cysts effectively whereas trophozoites and encysting parasites can recover from UV treatment at 100 mJ/cm(2) and 50 mJ/cm(2) respectively. Staining for phosphorylated histone H2A showed that UV treatment induces double-stranded DNA breaks and flow cytometry analyses revealed that UV treatment of trophozoites induces DNA replication arrest. Active DNA replication coupled to DNA repair could be an explanation to why UV light does not kill trophozoites and encysting cells as efficiently as the non-replicating cysts. We also examined UV-induced gene expression responses in both trophozoites and cysts using RNA sequencing (RNA seq). UV radiation induces small overall changes in gene expression in Giardia but cysts show a stronger response than trophozoites. Heat shock proteins, kinesins and Nek kinases are up-regulated, whereas alpha-giardins and histones are down-regulated in UV treated trophozoites. Expression of variable surface proteins (VSPs) is changed in both trophozoites and cysts. Our data show that Giardia cysts have limited ability to repair UV-induced damage and this may have implications for drinking- and waste-water treatment when setting criteria for the use of UV disinfection to ensure safe water. Copyright © 2015 Elsevier Inc. All rights reserved.
    No preview · Article · Mar 2015 · Experimental Parasitology
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    • "The drying step is avoided in the drop-cryo procedure for SEM preparations, which enables a better 3D preservation of the chromosomes and a visualization of sister chromatids lying closely together is therefore difficult (Wanner and Schroeder-Reiter 2008). The protein inventory for sister chromatid cohesion in Giardia is strikingly reduced; we and others failed to identify a homolog of the Rad21/Scc1, which, together with the SMC1 and SMC3 heterodimer, is essential for the formation of the tripartite cohesin ring (Eme et al. 2011; Malik et al. 2008; Ramesh et al. 2005). Although sister chromatids in Giardia chromosomes are held together until anaphase, the cohesion and splitting mechanisms remain unclear . "
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    ABSTRACT: During mitotic prophase, chromosomes of the pathogenic unicellular eukaryote Giardia intestinalis condense in each of the cell's two nuclei. In this study, Giardia chromosomes were investigated using light microscopy, high-resolution field emission scanning electron microscopy, and in situ hybridization. For the first time, we describe the overall morphology, condensation stages, and mitotic segregation of these chromosomes. Despite the absence of several genes involved in the cohesion and condensation pathways in the Giardia genome, we observed chromatin organization similar to those found in eukaryotes, i.e., 10-nm nucleosomal fibrils, 30-nm fibrils coiled to chromomeres or in parallel arrangements, and closely aligned sister chromatids. DNA molecules of Giardia terminate with telomeric repeats that we visualized on each of the four chromatid endings of metaphase chromosomes. Giardia chromosomes lack primary and secondary constrictions, thus preventing their classification based on the position of the centromere. The anaphase poleward segregation of sister chromatids is atypical in orientation and tends to generate lagging chromatids between daughter nuclei. In the Giardia genome database, we identified two putative members of the kleisin family thought to be responsible for condensin ring establishment. Thus far, Giardia chromosomes (300 nm to 1.5 μm) are the smallest chromosomes that were analyzed at the ultrastructural level. This study complements the existing molecular and sequencing data on Giardia chromosomes with cytological and ultrastructural information.
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    • "The best-characterized mechanism of ploidy change is sexual reproduction, which is thought to have evolved once very early in the eukaryotic lineage. Thus, factors regulating meiosis and recombination are conserved from fungi to man (Keeney 2001; Ramesh et al. 2005; Schurko and Logsdon 2008). Our understanding of sex has been greatly bolstered by studies in unicellular model yeasts such as S. cerevisiae and S. pombe. "
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    ABSTRACT: Human fungal pathogens can exist in a variety of ploidy states, including euploid and aneuploid forms. Ploidy change has a major impact on phenotypic properties, including the regulation of interactions with the human host. In addition, the rapid emergence of drug-resistant isolates is often associated with the formation of specific supernumerary chromosomes. Pathogens such as Candida albicans and Cryptococcus neoformans appear particularly well adapted for propagation in multiple ploidy states with novel pathways driving ploidy variation. In both species, heterozygous cells also readily undergo loss of heterozygosity (LOH), leading to additional phenotypic changes such as altered drug resistance. Here, we examine the sexual and parasexual cycles that drive ploidy variation in human fungal pathogens and discuss ploidy and LOH events with respect to their far-reaching roles in fungal adaptation and pathogenesis.
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