Some Blood Sporozoans from East African Reptiles*

SYNOPSIS. Six hundred and forty-one lizards belonging to 28 species, and 29 snakes belonging to 12 species from East Africa were examined for blood sporozoans. Eight species of lizards and 4 of snakes were positive. Tissue phases were seen in some infections; no proven arthropod vectors were found. Parasites are described from previously unreported hosts; new host records, and new stages in the life histories of previously named parasites are reported. The sporozoans belong to the genera Plasmodium, Haemoproteus, Haemogregarina or Hepatozoon, and probably Pirhemocyton. Reasons are given for the inadvisability of establishing new species of some of these on the basis of blood stages alone.     

Uniting sex and eukaryote origins in an emerging oxygenic world

Background  

Theories about eukaryote origins (eukaryogenesis) need to provide unified explanations for the emergence of diverse complex features that define this lineage. Models that propose a prokaryote-to-eukaryote transition are gridlocked between the opposing "phagocytosis first" and "mitochondria as seed" paradigms, neither of which fully explain the origins of eukaryote cell complexity. Sex (outcrossing with meiosis) is an example of an elaborate trait not yet satisfactorily addressed in theories about eukaryogenesis. The ancestral nature of meiosis and its dependence on eukaryote cell biology suggest that the emergence of sex and eukaryogenesis were simultaneous and synergic and may be explained by a common selective pressure.     

Construction of bacteria–eukaryote synthetic mutualism

Mutualism is ubiquitous in nature but is known to be intrinsically vulnerable with regard to both population dynamics and evolution. Synthetic ecology has indicated that it is feasible for organisms to establish novel mutualism merely through encountering each other by showing that it is feasible to construct synthetic mutualism between organisms. However, bacteria–eukaryote mutualism, which is ecologically important, has not yet been constructed. In this study, we synthetically constructed mutualism between a bacterium and a eukaryote by using two model organisms. We mixed a bacterium, Escherichia coli (a genetically engineered glutamine auxotroph), and an amoeba, Dictyostelium discoideum, in 14 sets of conditions in which each species could not grow in monoculture but potentially could grow in coculture. Under a single condition in which the bacterium and amoeba mutually compensated for the lack of required nutrients (lipoic acid and glutamine, respectively), both species grew continuously through several subcultures, essentially establishing mutualism. Our results shed light on the establishment of bacteria–eukaryote mutualism and indicate that a bacterium and eukaryote pair in nature also has a non-negligible possibility of establishing novel mutualism if the organisms are potentially mutualistic.     

寇氏隐甲藻（Crypthecodinium cohnii）细胞核骨架与中间纤维...

Nuclear matrix (NM) and intermediate filament (IF) scaffold in primitive eukaryote Crypthecodinium cohnii were shown using selective extraction together with embedment-free electron microscopy, whole mount cell preparation and immunoblot techniques. There exists a delicate NM-IF network spreading over cytoplasm and nucleus in dinoflagellate cells, however, nuclear lamina is undeveloped. The diameter of NM fiber is about 3-5 nm and IF is 10 nm. Chromosomes are connected with NM filament network. Immunoblot analysis showed that dinoflagellate contained keratin-like polypeptides (63 kD and 67 kD) while mammalian lamin antibodies did not crossreact with dinoflagellate total protein. Our experiment results demonstrated that a framework similar to NM-IF scaffold in mammalian cell appeared in primitive eukaryote. We propose that: (1) NM-IF scaffold is not restrict to vertebrate cell, and it may be originated from early stages of eukaryote evolution; (2) Keratin is probably very conservative; (3) Compared with IF, lamina might appear late in evolution, and some of primitive characteristics of dinoflagellate nucleus may be related to the lack of lamina.     

Molecular detection of the oyster parasite Mikrocytos mackini,and a preliminary phylogenetic analysis

The protistan parasite Mikrocytos mackini, the causative agent of Denman Island disease in the oyster Crassostrea gigas in British Columbia, Canada, is of wide concern because it can infect other oyster species and because its life cycle, mode of transmission, and origins are unknown. PCR and fluorescent in situ hybridization (FISH) assays were developed for M. mackini, the PCR assay was validated against standard histopathological diagnosis, and a preliminary phylogenetic analysis of the M. mackini small-subunit ribosomal RNA gene (SSU rDNA) was undertaken. A PCR designed specifically not to amplify host DNA generated a 544 bp SSU rDNA fragment from M. mackini-infected oysters and enriched M. mackini cell isolates, but not from uninfected control oysters. This fragment was confirmed by FISH to be M. mackini SSU rDNA. A M. mackini-specific PCR was then designed which detected 3 to 4x more M. mackini infections in 1056 wild oysters from Denman Island, British Columbia, than standard histopathology. Mikrocytos mackini prevalence estimates based on both PCR and histopathology increased (PCR from 4.4 to 7.4%, histopathology from 1.2 to 2.1%) when gross lesions were processed in addition to standard samples (i.e. transverse sections for histopathology, left outer palp DNA for PCR). The use of histopathology and tissue imprints plus PCR, and standard samples plus observed gross lesions, represented a 'total evidence' approach that provided the most realistic estimates of the true prevalence of M. mackini. Maximum parsimony and evolutionary distance phylogenetic analyses suggested that M. mackini may be a basal eukaryote, although it is not closely related to other known protistan taxa.     

Effect of viral preinfection upon cell adherence in some staphylococcus strains from specific infections or carriers

The adherence of bacteria to eukaryote cells has been largely investigated as an essential step in the occurrence of bacterial infection. Some clinical and epidemiological studies have revealed the frequent association of certain viral infections with bacterial infections originating in the same ecological niche. Therefore, we investigated the effect of the viral preinfection (ADV4) of some cultivated cells (HEp-2 and IC.SK-27) upon the adherence of staphylococcus to these cells. The analysis of cell adherence within the mentioned conditions, estimated by flow cytometry, allowed of the following conclusions: 1. bacterial adherence to cultivated and virally preinfected cells is augmented by the viral preinfection, and its value on a given cell substrate may characterize a bacterial strain; 2. bacterial adherence to the investigated cell substrates does not correlate with the origin of the tested staphylococcus strains (infections or carriers) and some cell lines can differentiate bacterial strains depending upon the ecological niche or inside it.     

Telomere, telomerase, tumorigenesis and therapy: an overview

The ends of chromosome in higher eukaryote are termed telomere. The DNAs present at that part of chromosome is called telomeric DNA. Telomeric DNA consists of tandemly repeated DNA sequences. The replication of the ends of chromosomes is not controlled by conventional DNA polymerases rather a special kind of enzyme is involved in this process. It is a ribonucleoprotein and known as telomerase. Cells in senescence stage face telomeric crisis that leads to loss of telomeric ends. Surveillance turns to procancer cells with increased telomerase activity which is a later consequence. Based on these facts a key diagnostic approach has been developed for detection of tumour. A novel therapy for tumour repression has been developed using telomerase inhibitors. However, these inhibitors are very much effective for solid tumour therapy and conceptually will not work on hematological malignancies.     

Small GTPases and the evolution of the eukaryotic cell

The origin of eukaryotes is one of the major challenges of evolutionary cell biology. Other than the endosymbiotic origin of mitochondria and chloroplasts, the steps leading to eukaryotic endomembranes and endoskeleton are poorly understood. Ras-family small GTPases are key regulators of cytoskeleton dynamics, vesicular trafficking and nuclear function. They are specific for eukaryotes and their expansion probably traces the evolution of core eukaryote features. The phylogeny of small GTPases suggests that the first endomembranes to evolve during eukaryote evolution had secretory, and not phagocytic, function. Based on the reconstruction of putative roles for ancestral small GTPases, a hypothetical scenario on the origins of the first endomembranes, the nucleus, and phagocytosis is presented.     

Haemogregarina pseudemydis n. sp. (Apicomplexa: Haemogregarinidae) and Pirhemocyton chelonarum n. sp. in Turtles from Louisiana*

SYNOPSIS. The blood of each of 95 turtles (8 species) collected from southeastern Louisiana was infected with some or all of the merogonic stages and gametocyte stage of Haemogregarina pseudemydis n. sp. Five species of turtles harbored Pirhemocyton chelonarum n. sp. Turtle Haemogregarina and Pirhemocyton are locality records for Louisiana. Pirhemocyton is reported for the first time in turtles and in the continental U.S.A.     

Subtype analysis and prevalence of mixed subtype infection of Blastocystis in farmed pigs from Chiba Prefecture,Japan

Blastocystis is an intestinal eukaryote found globally in humans and a wide range of animals. Blastocystis has been reported in domestic pigs, with subtype (ST) 5 being the most dominant, followed by ST1 and ST3. PCR-sequencing is commonly used for ST identification in pigs, but it often results in an underestimation of the prevalence of mixed infections. Here, we aimed to investigate the ST distribution and prevalence of mixed ST infections of Blastocystis in pigs from Chiba Prefecture in eastern Japan. A total of 82 fecal samples positive for Blastocystis were collected from two different farms, A and B. PCR was performed using ST-specific primers for ST1, ST2, ST3, and ST5. The prevalence of single ST5 infections was 37.8% (31/82), whereas that of mixed infections with ST5 and other STs was 57.3% (47/82) . A high percentage of single ST5 infections was observed in sows, piglets, and weaners from farm A (13/15, 86.7%), whereas mixed infections of ST5 and other STs (ST1 and ST3) were observed in 3- to 5-month-old grower pigs (15/18, 83.3%). Similarly, in farm B, most sows and piglets under 1 month of age showed a single ST5 infections (12/17, 70.6%), whereas weaner, grower, and finisher pigs showed mixed infections with ST5 and other STs, including ST1, ST2, and ST3 (27/28, 96.4%). In domestic pigs, diet and rearing environments change dramatically over the course of the animal's lifetime, which may have caused this difference in the prevalence of mixed ST infections among different age groups.     

Phylogenetic Analysis of Eukaryotes Using Heat-Shock Protein Hsp90

Most eukaryote molecular phylogenies have been based on small-subunit ribosomal RNA as its database includes the most species, but serious problems have been encountered that can make these trees misleading. More recent studies using concatenated protein sequences have increased the data per organism, reducing misleading signals from a single sequence, but taxon sampling is limited. To increase the database of protein-coding genes we sequenced the cytosolic form of heat-shock protein Hsp90 from a broad variety of previously unsampled eukaryote groups: protozoan flagellates (phyla Choanozoa, Apusozoa, Cercozoa) and all three groups of chromists (Cryptophyta, Heterokonta, Haptophyta). Gamma-corrected distance trees robustly show three groups: bacterial sequences are sister to all eukaryote sequences, which are cleanly subdivided into the cytosolic sequences and a clade comprising the chloroplast and endoplasmic reticulum (ER) Hsp90 sequences. The eukaryote cytosolic sequences comprise a robust opisthokont clade (animals/Choanozoa/fungi), a bikont clade, and an amoebozoan branch. However their topology is not robust. When the cytosolic sequences are rooted using only the ER/chloroplast clade as outgroup the amoebozoan Dictyostelium is sister to the opisthokonts forming a unikont clade in the distance tree. Congruence of this tree with that for concatenated mitochondrial proteins suggests that the root of the eukaryote tree is between unikonts and bikonts. Gamma-corrected maximum likelihood analyses of cytosolic sequences alone (519 unambiguously aligned amino acid positions) show bikonts as a clade, as do least-squares distance trees, but with other distance methods and parsimony the sole amoebozoan species branches weakly within bikonts. Choanozoa are clearly sisters to animals. Some major bikont groups (e.g. green plants, alveolates, Euglenozoa) are consistently recovered, but others (e.g. discicristates, chromalveolates) appear only in some trees; the backbone of the bikont subtree is not resolved, the position of groups represented only by single sequences being particularly unclear. Although single-gene trees will probably never resolve these uncertainties, the congruence of Hsp90 trees with other data is greater than for most other molecules and further taxon sampling of this molecule is recommended.     

Frataxin, a conserved mitochondrial protein, in the hydrogenosome of Trichomonas vaginalis

Recent data suggest that frataxin plays a key role in eukaryote cellular iron metabolism, particularly in mitochondrial heme and iron-sulfur (FeS) cluster biosynthesis. We have now identified a frataxin homologue (T. vaginalis frataxin) from the human parasite Trichomonas vaginalis. Instead of mitochondria, this unicellular eukaryote possesses hydrogenosomes, peculiar organelles that produce hydrogen but nevertheless share common ancestry with mitochondria. T. vaginalis frataxin contains conserved residues implicated in iron binding, and in silico, it is predicted to form a typical alpha-beta sandwich motif. The short N-terminal extension of T. vaginalis frataxin resembles presequences that target proteins to hydrogenosomes, a prediction confirmed by the results of overexpression of T. vaginalis frataxin in T. vaginalis. When expressed in the mitochondria of a frataxin-deficient Saccharomyces cerevisiae strain, T. vaginalis frataxin partially restored defects in heme and FeS cluster biosynthesis. Although components of heme synthesis or heme-containing proteins have not been found in T. vaginalis to date, T. vaginalis frataxin was also shown to interact with S. cerevisiae ferrochelatase by using a Biacore assay. The discovery of conserved iron-metabolizing pathways in mitochondria and hydrogenosomes provides additional evidence not only of their common evolutionary history, but also of the fundamental importance of this pathway for eukaryotes.     

Megaphylogeny,Cell Body Plans,Adaptive Zones: Causes and Timing of Eukaryote Basal Radiations1

ABSTRACT. I discuss eukaryote megaphylogeny and the timing of major innovations in the light of multigene trees and the rarity of marine/freshwater evolutionary transitions. The first eukaryotes were aerobic phagotrophs, probably substratum‐associated heterotrophic amoeboflagellates. The primary eukaryote bifurcation generated unikonts (ancestrally probably unicentriolar, with a conical microtubular [MT] cytoskeleton) and bikonts (ciliary transformation from anterior cilium to ancestrally gliding posterior cilium; cytoskeleton of ventral MT bands). Unikonts diverged into Amoebozoa with anterior cilia, lost when lobosan broad pseudopods evolved for locomotion, and Choanozoa with posterior cilium and filose pseudopods that became unbranched tentacles/microvilli in holozoa and eventually the choanoflagellate/choanocyte collar. Of choanozoan ancestry, animals evolved epithelia, fibroblasts, eggs, and sperm. Fungi and Ichthyosporea evolved walls. Bikonts, ancestrally with ventral grooves, include three adaptively divergent megagroups: Rhizaria (Retaria and Cercozoa, ancestrally reticulofilose soft‐surfaced gliding amoeboflagellates), and the originally planktonic Excavata, and the corticates (Plantae and chromalveolates) that suppressed pseudopodia. Excavata evolved cilia‐generated feeding currents for grooval ingestion; corticates evolved cortical alveoli and ciliary hairs. Symbiogenetic origin and transfers of chloroplasts stimulated an explosive radiation of corticates—hard to resolve on multigene trees—and opisthokonts, and ensuing Cambrian explosions of animals and protists. Plantae lost phagotrophy and multiply evolved walls and macroalgae. Apusozoa, with dorsal pellicle and ventral pseudopods, are probably the most divergent bikonts or related to opisthokonts. Eukaryotes probably originated 800–850 My ago. Amoebozoa, Apusozoa, Loukozoa, and Metamonada may be the only extant eukaryote phyla pre‐dating Neoproterozoic snowball earth. New subphyla are established for Choanozoa and Loukozoa; Amoebozoa are divided into three revised subphyla, with Variosea transferred into Conosa.     

Collodictyon--an ancient lineage in the tree of eukaryotes

The current consensus for the eukaryote tree of life consists of several large assemblages (supergroups) that are hypothesized to describe the existing diversity. Phylogenomic analyses have shed light on the evolutionary relationships within and between supergroups as well as placed newly sequenced enigmatic species close to known lineages. Yet, a few eukaryote species remain of unknown origin and could represent key evolutionary forms for inferring ancient genomic and cellular characteristics of eukaryotes. Here, we investigate the evolutionary origin of the poorly studied protist Collodictyon (subphylum Diphyllatia) by sequencing a cDNA library as well as the 18S and 28S ribosomal DNA (rDNA) genes. Phylogenomic trees inferred from 124 genes placed Collodictyon close to the bifurcation of the "unikont" and "bikont" groups, either alone or as sister to the potentially contentious excavate Malawimonas. Phylogenies based on rDNA genes confirmed that Collodictyon is closely related to another genus, Diphylleia, and revealed a very low diversity in environmental DNA samples. The early and distinct origin of Collodictyon suggests that it constitutes a new lineage in the global eukaryote phylogeny. Collodictyon shares cellular characteristics with Excavata and Amoebozoa, such as ventral feeding groove supported by microtubular structures and the ability to form thin and broad pseudopods. These may therefore be ancient morphological features among eukaryotes. Overall, this shows that Collodictyon is a key lineage to understand early eukaryote evolution.     

The bacterial toxin RelE induces specific mRNA cleavage in the A site of the eukaryote ribosome

RelE/RelB is a well-characterized toxin-anti-toxin pair involved in nutritional stress responses in Bacteria and Archae. RelE lacks any eukaryote homolog, but we demonstrate here that it efficiently and specifically cleaves mRNA in the A site of the eukaryote ribosome. The cleavage mechanism is similar to that in bacteria, showing the feasibility of A-site cleavage of mRNA for regulatory purposes also in eukaryotes. RelE cleavage in the A-site codon of a stalled eukaryote ribosome is precise and easily monitored, making "RelE printing" a useful complement to toeprinting to determine the exact mRNA location on the eukaryote ribosome and to probe the occupancy of its A site.     

Eukaryotic and prokaryotic signal peptides direct secretion of a bacterial endoglucanase by mammalian cells

It is well established that hydrophobic signal sequences direct proteins into or across the endoplasmic reticulum membrane in eukaryotes and cell membranes in prokaryotes. Although it is recognized that eukaryote proteins are efficiently secreted by bacterial systems, the export of bacterial proteins by eukaryotes has received little attention. To investigate membrane translocation of bacterial proteins by mammalian cells, the secretion of a bacterial endoglucanase (endoglucanase E) from stably transfected Chinese hamster ovary cells has been examined. We report that a functional endoglucanase is secreted when fused to prokaryote or eukaryote signal peptides. Furthermore, the endoglucanase was post-translationally modified before secretion. Data presented in this paper suggest that secretion of bacterial proteins by eukaryote cells may be a general phenomenon and infer that there are no specific requirements with respect to the origin of the signal sequences.     

The distribution and evolutionary history of the PRP8 intein

Background  

We recently described a mini-intein in the PRP8 gene of a strain of the basidiomycete Cryptococcus neoformans, an important fungal pathogen of humans. This was the second described intein in the nuclear genome of any eukaryote; the first nuclear encoded intein was found in the VMA gene of several saccharomycete yeasts. The evolution of eukaryote inteins is not well understood. In this report we describe additional PRP8 inteins (bringing the total of these to over 20). We compare and contrast the phylogenetic distribution and evolutionary history of the PRP8 intein and the saccharomycete VMA intein, in order to derive a broader understanding of eukaryote intein evolution. It has been suggested that eukaryote inteins undergo horizontal transfer and the present analysis explores this proposal.     

A New Divergent Type of Eukaryotic Methionine Adenosyltransferase is Present in Multiple Distantly Related Secondary Algal Lineages

ABSTRACT. S‐adenosylmethionine is one of the most important metabolites in living cells and is synthesized in a single reaction catalyzed by methionine adenosyltransferase (MAT). At the sequence and structural level, this enzyme is one of the most conserved proteins known. Here we show that some representatives of three distantly related eukaryotic lineages—dinoflagellates, haptophytes, and euglenids—possess a highly divergent type of MAT, which we call MATX. Even though MATX contains all the sites known to be involved in catalysis and the association of monomers, it also has four insertions throughout the protein that are not observed in other MAT homologs. The phylogenetic distribution and affinities of MATX suggest that it originated in a single eukaryotic lineage and was spread via multiple events of eukaryote‐to‐eukaryote lateral gene transfer. We suggest a tentative model in which the origin of MATX is connected with the progression of secondary endosymbiosis.     

Molecular phylogeny of centrohelid heliozoa,a novel lineage of bikont eukaryotes that arose by ciliary loss

Abstract Recent molecular and cellular evidence indicates that eukaryotes comprise three major lineages: the probably ancestrally uniciliate protozoan phylum Amoebozoa; the ancestrally posteriorly uniciliate opisthokont clade (animals, Choanozoa, and fungi); and a very diverse ancestrally biciliate clade, the bikonts—plants, chromalveolates, and excavate and rhizarian Protozoa. As Heliozoa are the only eukaryote phylum not yet placed on molecular sequence trees, we have sequenced the 18S rRNA genes of three centrohelid heliozoa, Raphidiophrys ambigua, Heterophrys marina, and Chlamydaster sterni, to investigate their phylogenetic position. Phylogenetic analysis by distance and maximum likelihood methods allowing for intersite rate variation and invariable sites confirms that centrohelid heliozoa are a robust clade that does not fall within any other phyla. In particular, they are decisively very distant from the heterokont pedinellid chromists, at one time thought to be related to heliozoa, and lack the unique heterokont signature sequence. They also appear not to be specifically related to either Amoebozoa or Radiolaria, with which they have sometimes been classified, so it is desirable to retain Heliozoa as a separate protozoan phylum. Even though centrohelids have no cilia or centrioles, the centrohelid clade branches among the bikont eukaryotes, but there is no strong bootstrap support for any particular position. Distance trees usually place centrohelids as sisters to haptophytes, whereas parsimony puts them as sisters to red algae, but there is no reason to think that either position is correct; both have very low bootstrap support. Quartet puzzling places them with fairly low support as sisters to the apusozoan zooflagellate Ancyromonas. As Ancyromonas is the only other eukaryote that shares the character combination of flat plate-like mitochondrial cristae and kinetocyst-type extrusomes with centrohelids, this position is biologically plausible, but because of weak support and conflict between trees it might not be correct. Irrespective of their precise position, our trees (together with previous evidence that Chlamydaster sterni has the derived dihydrofolate reductase/thymidylate synthetase gene fusion unique to bikonts) indicate that centrohelid heliozoa are ancestrally derived from a bikont flagellate by the loss of cilia. The centroplast that nucleates their axonemal microtubules is therefore almost certainly homologous with the centrosome of ciliated eukaryotes and should simply be called a centrosome.