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At least 19 recordsLinked to original sources

PubMed2002

Clitellocephalus americanus n. gen., n. sp. (Apicomplexa: Eugregarinida: Gregarinidae) from Cratacanthus dubius (Coleoptera: Carabidae: Harpalinae) in the Nebraska sandhills and Clitellocephalus ophoni n. comb. (Apicomplexa: Eugregarinida: Gregarinidae) from Ophonus pubescens (Coleoptera: Carabidae: Harpalinae) in Sète, France.

Clitellocephalus americanus n. gen., n. sp. (Apicomplexa: Eugregarinida: Gregarinidae) is described from Cratacanthus dubius (Coleoptera: Carabidae) collected from Keith County in the Sandhills of western Nebraska. Clitellocephalus ophoni n. comb. is redescribed using original type material from Ophonus pubescens (Coleoptera: Carabidae) collected in Sète, France. Clitellocephalus n. gen. is distinguished by a deltoid epimerite with an internal anterior obconoid structure and a basal toroidal vacuole, which is retained in gamonts. Protomerites are broadly elliptical to cylindrical; deutomerites are narrowly obovate. Association is precocious, caudofrontal, and biassociative, with the satellite protomerite engulfing the posterior end of the primite deutomerite to form an interlock. Gametocysts are spherical. Sporoducts are present but reduced and irregular in number. Oocysts are dolioform, dehiscing in chains. The species described herein are differentiated by their overall size and relative proportion of cellular structures.

Animals↗

PubMed2001

Haemogregarine specificity in two communities of Florida snakes, with descriptions of six new species of Hepatozoon (Apicomplexa: Hepatozoidae) and a possible species of Haemogregarina (Apicomplexa: Haemogregarinidae).

Five species of snakes in Florida, from Palm Beach County in the south and Alachua County 450 km to the north, occur in similar habitat but have distinctive Hepatozoon species characteristic of each host species. In Palm Beach County, Diadophis punctatus is host to Hepatozoon punctatus n. sp., Thamnophis sauritus sackenii to Hepatozoon sauritus n. sp., and Nerodia fasciata pictiventris to Hepatozoon pictiventris n. sp. In Alachua County, N. fasciata pictiventris is parasitized by Hepatozoon fasciatae n. sp., Seminatrix p. pygaea by Hepatozoon seminatrici n. sp., and Thamnophis s. sirtalis by Hepatozoon sirtalis n. sp. Each Hepatozoon sp. has distinctive gamonts and sporogonic characters and, in the 4 species where known, meronts. Nerodia floridana is host to Haemogregarina floridana n. sp. in both localities, with generic identification tentative, based upon presence of erythrocytic meronts. The presence of sporocysts in the proboscis of 31% of Aedes aegypti infected by H. pictiventris is the first report of infective stages of a reptilian Hepatozoon species within the mouthparts of a dipteran vector. This study suggests that in Florida, at least, the diversity of the Hepatozoon community not only equals but probably exceeds the diversity of the snake communities present, and that host specificity in nature may be much greater than that postulated from previous studies.

Aedes↗

PubMed2000

The plastid in Apicomplexa: what use is it?

An extrachromosomal genome of between 27 and 35 kb has been described in several apicomplexan parasites including Plasmodium falciparum and Toxoplasma gondii. Examination of sequence data proved the genomes to be a remnant plastid genome, from which all genes encoding photosynthetic functions had been lost. Localisation studies had shown that the genome was located within a multi-walled organelle, anterior to the nucleus. This organelle had been previously described in ultrastructural studies of several genera of apicomplexa, but no function had been attributed to it. This invited review describes the evolution of knowledge on the apicomplexan plastid, then discusses current research findings on the likely role of the plastid in the Apicomplexa. How the plastid may be used to effect better drug treatments for apicomplexan diseases, and its potential as a marker for investigating phylogenetic relationships among the Apicomplexa, are discussed.

Animals↗

PubMed2001

Gliding motility and cell invasion by Apicomplexa: insights from the Plasmodium sporozoite.

Apicomplexa constitute one of the largest phyla of protozoa. Most Apicomplexa, including those pathogenic to humans, are obligate intracellular parasites. Their extracellular forms, which are highly polarized and elongated cells, share two unique abilities: they glide on solid substrates without changing their shape and reach an intracellular compartment without active participation from the host cell. There is now ample ultrastructural evidence that these processes result from the backward movement of extracellular interactions along the anteroposterior axis of the parasite. Recent work in several Apicomplexa, including genetic studies in the Plasmodium sporozoite, has provided molecular support for this 'capping' model. It appears that the same machinery drives both gliding motility and host cell invasion. The cytoplasmic motor, a transmembrane bridge and surface ligands essential for cell invasion are conserved among the main apicomplexan pathogens.

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PubMedDate not supplied

[Further comment on the coccidian nature of cryptosporidia (Sporozoa: Apicomplexa)].

The coccidian nature of the genus Cryptosporidium was undoubtedly accepted by Tyzzer who was the first to describe this sporozoan parasite in 1907. Electron microscopic studies made in 70-90s demonstrated the intracellular, although extracytoplasmic localization of Cryptosporidium spp. The pattern of Cryptosporidium life cycle fits well that of other intestinal homogeneous coccidian genera of the suborder Eimeriina: macro- and microgamonts develop independently, a microgamont gives rise to numerous male gametes, oocysts serving for parasite's spreading in the environment. Along with these characters, Cryptosporidium spp. demonstrate some secondary peculiarities (an endogenous phase of development in microvilli of epithelial surfaces, two morphofunctional types of oocysts, the smallest number of sporozoites per oocyst, a multi-membraneous "feeder" organelle etc.), which may be due presumably to their early acquisition of specialization in the course of evolution. The recent studies based on molecular sequence data (18S rRNA) applied to 8 eimeriid and isosporid coccidian genera (Morrison, Ellis, 1997), suggested that the subclass Coccidia (class, according to Morrison and Ellis) be considered monophylic if Cryptosporidium were excluded, and this genus was regarded as the sister group to the rest of the Apicomplexa, or as the sister to the suborder (class) Hematozoa within the Apicomplexa. Either of these placements of Cryptosporidium definitely conflicts with both the generally accepted taxonomic scheme by Levine (1982) and the phenotypically based phylogeny of the phylum Apicomplexa (Barta e. a., 1990). The author's opinion is that the differences between the examined eimeriid and isosporid coccidia, on the one hand, and Cryptosporidium, on the other hand, provided by molecular sequence data, may testify primarily to the well known morphofunctional dissimilarities between the compared organisms, rather than cast doubt on the coccidian nature of Cryptosporidium. Again, these data can hardly prove that Cryptosporidium does not belong to the coccidia. Thus, the modern molecular sequence data, despite their obvious scientific value, would make sense for phylogeny estimation only, if they are critically analysed and considered in combination with results of the relevant basic research.

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PubMed1991

Evolutionary relationships of avian Eimeria species among other Apicomplexan protozoa: monophyly of the apicomplexa is supported.

Direct, reverse transcriptase-mediated, partial sequencing of the small-subunit (16S-like) ribosomal RNA (srRNA) of Eimeria tenella and E. acervulina was performed. Sequences were aligned by eye with six previously published, partial or complete srRNA sequences of apicomplexan protists (Plasmodium berghei, Theileria annulata, Cryptosporidium sp., Toxoplasma gondii, Sarcocystis muris, and S. gigantea). Six eukaryotic protists (a slime mold, a yeast, two dinoflagellates, and two ciliates) acted as an outgroup for a parsimony-based phylogenetic analysis (PAUP Ver. 3.0). The 188 phylogenetically informative sites (i.e., those positions that neither were unvaried nor had only autapomorphic substitutions) supported a single tree topology 481 steps in length with a consistency index of 0.65 in which the monophyly of the Apicomplexa was supported. The two Eimeria species and S. muris, S. gigantea, and T. gondii formed a pair of monophyletic groups that were sister groups. The two Sarcocystis species were not hypothesized to be sister taxa. The genera Plasmodium and Cryptosporidium were hypothesized to form the sister group to these five coccidia and T. annulata. A priori data-editing techniques that deleted "variable" positions prior to analysis failed to recognize the monophyly of the Apicomplexa when the same parsimony-based tree-building algorithm was used. Inability of the outgroup taxa to root the well-supported ingroup tree (Apicomplexa) at a unique site when these taxa were used individually for this purpose reinforces the need for an appropriate, multiple-taxon outgroup in such analyses.

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PubMed1997

Investigating phylogenetic relationships within the Apicomplexa using sequence data: the search for homology.

Whether stated explicitly or not, all molecular studies that seek to infer "homologies" among sequences or that attempt to determine the "relatedness" of taxa based on sequence comparisons are evolutionary studies. The generation of a reliable evolutionary hypothesis based on molecular sequences is dependent almost exclusively on the ability to align sequences such that bases or amino acids in the same position of two sequences are positionally homologous (i.e., they share the same position in the gene under study). The selection of suitable gene targets (commonly 18S small subunit rRNA gene sequences in the Apicomplexa) and appropriate ingroup and outgroup taxa will affect the ability to align sequences unambiguously. Mathematically derived alignments based on local sequence similarity have been shown to be less reliable than alignments based on conserved secondary structures coupled with an analysis of compensatory base changes. Use of staggered sequence alignments through hypervariable regions of 18S small subunit rRNA gene sequences in which subsets of taxa are aligned independently may permit inclusion of more of the primary sequences with an associated increase in information content in the data set. The use of these highly variable regions is critical for determining the branching order of closely related terminal taxa in the phylum Apicomplexa.

Animals↗

PubMed2006

Fine structure and putative feeding mechanism of the archigregarine Selenidium orientale (Apicomplexa: Gregarinomorpha).

Archigregarines are considered one of the most plesiomorphic groups of Apicomplexa. Until recently, however, this viewpoint was based mainly on the results of the detailed investigation of a single species, Selenidium hollandei. The present study of the fine structure of trophozoites of another archigregarine species Selenidium orientale Bogolepova, 1953. (Apicomplexa, Archigregarinida, as proposed by Grassé and Schrével), with special reference to the forebody structure of the attached individuals, allows more confident discussion of the plesiomorphic status of the archigregarines. Specimens of S. orientale were collected from the midgut of the Pacific sipunculid Themiste pyroides Chamberlain, 1920. The ultrastructure of the trophozoites generally corresponds to that of other studied species of Selenidium. Differences in the forebody structure between S. orientale and S. hollandei do not conflict with Schrével's hypothesis on the feeding function of the apical complex in archigregarine trophozoites, although they suggest that, in S. orientale at least, the cytostome is not a persistent structure, but re-opens for each sucking event, and Selenidium trophozoites feed by intermittent sucking of host cytoplasm. Microtubules in the axial zone of the mucron neck may mediate the transport of food vacuoles.

Animals↗

PubMed2004

A first glimpse into the pattern and scale of gene transfer in Apicomplexa.

Reports of plant-like and bacterial-like genes for a number of parasitic organisms, most notably those within the Apicomplexa and Kinetoplastida, have appeared in the literature over the last few years. Among the apicomplexan organisms, following discovery of the apicomplexan plastid (apicoplast), the discovery of plant-like genes was less surprising although the extent of transfer and the relationship of transferred genes to the apicoplast remained unclear. We used new genome sequence data to begin a systematic examination of the extent and origin of transferred genes in the Apicomplexa combined with a phylogenomic approach to detect potential gene transfers in four apicomplexan genomes. We have detected genes of algal nuclear, chloroplast (cyanobacterial) and proteobacterial origin. Plant-like genes were detected in species not currently harbouring a plastid (e.g. Cryptosporidium parvum) and putatively transferred genes were detected that appear to be unrelated to the function of the apicoplast. While the mechanism of acquisition for many of the identified genes is not certain, it appears that some were most likely acquired via intracellular gene transfer from an algal endosymbiont while others may have been acquired via horizontal gene transfer.

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PubMed2005

Dense granules: are they key organelles to help understand the parasitophorous vacuole of all apicomplexa parasites?

Together with micronemes and rhoptries, dense granules are specialised secretory organelles of Apicomplexa parasites. Among Apicomplexa, Plasmodium represents a model of parasites propagated by way of an insect vector, whereas Toxoplasma is a model of food borne protozoa forming cysts. Through comparison of both models, this review summarises data accumulated over recent years on alternative strategies chosen by these parasites to develop within a parasitophorous vacuole and explores the role of dense granules in this process. One of the characteristics of the Plasmodium erythrocyte stages is to export numerous parasite proteins into both the host cell cytoplasm and/or plasma membrane via the vacuole used as a step trafficking compartment. Whether this feature can be correlated to few storage granules and a restricted number of dense granule proteins, is not yet clear. By contrast, the Toxoplasma developing vacuole is decorated by abundantly expressed dense granule proteins and is characterised by a network of membranous nanotubes. Although the exact function of most of these proteins remains currently unknown, recent data suggest that some of these dense granule proteins could be involved in building the intravacuolar membranous network. Conserved expression of the Toxoplasma dense granule proteins throughout most of the parasite stages suggests that they could also be key elements of the cyst formation.

Animals↗

PubMed2005

Rhomboid-like proteins in Apicomplexa: phylogeny and nomenclature.

Rhomboids form a family of polytopic intramembrane serine proteases. In Toxoplasma gondii, an essential activity called microneme protein protease 1 (MPP1) cleaves secreted adhesive proteins within their transmembrane domains, at a site conserved in similar proteins of other Apicomplexa. Current evidence suggests that MPP1 is ubiquitous in the phylum and is encoded by a rhomboid gene. In this article, we present the current repertoire of rhomboid-like proteins in Apicomplexa using a nomenclature based on phylogenetic analyses.

Amino Acid Sequence↗

PubMed1997

'Total evidence' refutes the inclusion of Perkinsus species in the phylum Apicomplexa.

The phylogenetic affinities of the oyster pathogen Perkinsus marinus were investigated with morphology, 18S-like rDNA data and actin sequence data. Morphological investigations revealed that Perkinsus species do not have a conoid and that other criteria which have been used to place them in the Apicomplexa are general to alveolates. When considered separately, 18S-like rDNA and actin data sets each support a closer affinity for Perkinsus marinus with the dinoflagellates. However, each of these separate analyses possess their own biases and weaknesses. Use of the phylogenetic principle of 'total evidence' in which data sets are combined in simultaneous analysis yielded a more robust hypothesis that is stable both to character and taxonomic sampling. The resulting cladogram strongly corroborates the placement of Perkinsus species with the Dinoflagellida and not with the Apicomplexa.

Actins↗

PubMed1995

Evolutionary origin of Plasmodium and other Apicomplexa based on rRNA genes.

We have explored the evolutionary history of the Apicomplexa and two related protistan phyla, Dinozoa and Ciliophora, by comparing the nucleotide sequences of small subunit ribosomal RNA genes. We conclude that the Plasmodium lineage, to which the malarial parasites belong, diverged from other apicomplexan lineages (piroplasmids and coccidians) several hundred million years ago, perhaps even before the Cambrian. The Plasmodium radiation, which gave rise to several species parasitic to humans, occurred approximately 129 million years ago; Plasmodium parasitism of humans has independently arisen several times. The origin of apicomplexans (Plasmodium), dinoflagellates, and ciliates may be > 1 billion years old, perhaps older than the three multicellular kingdoms of animals, plants, and fungi. Digenetic parasitism independently evolved several times in the Apicomplexa.

Animals↗

PubMed1997

Effects of nucleotide sequence alignment on phylogeny estimation: a case study of 18S rDNAs of apicomplexa.

The reconstruction of phylogenetic history is predicated on being able to accurately establish hypotheses of character homology, which involves sequence alignment for studies based on molecular sequence data. In an empirical study investigating nucleotide sequence alignment, we inferred phylogenetic trees for 43 species of the Apicomplexa and 3 of Dinozoa based on complete small-subunit rDNA sequences, using six different multiple-alignment procedures: manual alignment based on the secondary structure of the 18S rRNA molecule, and automated similarity-based alignment algorithms using the PileUp, ClustalW, TreeAlign, MALIGN, and SAM computer programs. Trees were constructed using neighboring-joining, weighted-parsimony, and maximum-likelihood methods. All of the multiple sequence alignment procedures yielded the same basic structure for the estimate of the phylogenetic relationship among the taxa, which presumably represents the underlying phylogenetic signal. However, the placement of many of the taxa was sensitive to the alignment procedure used; and the different alignments produced trees that were on average more dissimilar from each other than did the different tree-building methods used. The multiple alignments from the different procedures varied greatly in length, but aligned sequence length was not a good predictor of the similarity of the resulting phylogenetic trees. We also systematically varied the gap weights (the relative cost of inserting a new gap into a sequence or extending an already-existing gap) for the ClustalW program, and this produced alignments that were at least as different from each other as those produced by the different alignment algorithms. Furthermore, there was no combination of gap weights that produced the same tree as that from the structure alignment, in spite of the fact that many of the alignments were similar in length to the structure alignment. We also investigated the phylogenetic information content of the helical and nonhelical regions of the rDNA, and conclude that the helical regions are the most informative. We therefore conclude that many of the literature disagreements concerning the phylogeny of the Apicomplexa are probably based on differences in sequence alignment strategies rather than differences in data or tree-building methods.

Algorithms↗

PubMed2003

Gene discovery in the apicomplexa as revealed by EST sequencing and assembly of a comparative gene database.

Large-scale EST sequencing projects for several important parasites within the phylum Apicomplexa were undertaken for the purpose of gene discovery. Included were several parasites of medical importance (Plasmodium falciparum, Toxoplasma gondii) and others of veterinary importance (Eimeria tenella, Sarcocystis neurona, and Neospora caninum). A total of 55192 ESTs, deposited into dbEST/GenBank, were included in the analyses. The resulting sequences have been clustered into nonredundant gene assemblies and deposited into a relational database that supports a variety of sequence and text searches. This database has been used to compare the gene assemblies using BLAST similarity comparisons to the public protein databases to identify putative genes. Of these new entries, approximately 15%-20% represent putative homologs with a conservative cutoff of p < 10(-9), thus identifying many conserved genes that are likely to share common functions with other well-studied organisms. Gene assemblies were also used to identify strain polymorphisms, examine stage-specific expression, and identify gene families. An interesting class of genes that are confined to members of this phylum and not shared by plants, animals, or fungi, was identified. These genes likely mediate the novel biological features of members of the Apicomplexa and hence offer great potential for biological investigation and as possible therapeutic targets.

Animals↗

PubMedDate not supplied

Phylogeny of the large extrachromosomal DNA of organisms in the phylum Apicomplexa.

Organisms in the phylum Apicomplexa appear to have a large extrachromosomal DNA which is unrelated to the mitochondrial DNA. Based on the apparent gene content of the large (35 kb) extrachromosomal DNA of Plasmodium falciparum, it has been suggested that it is a plastid-like DNA, which may be related to the plastid DNA of rhodophytes. However, phylogenetic analyses have been inconclusive. It has been suggested that this is due to the unusually high A+T content of the Plasmodium falciparum large extrachromosomal DNA. To further investigate the evolution of the apicomplexan large extrachromosomal DNA, the DNA sequence of the organellar ribosomal RNA gene from Toxoplasma gondii, was determined. The Toxoplasma gondii rDNA sequence was most similar to the large extrachromosomal rDNA of Plasmodium falciparum, but was much less A+T rich. Phylogenetic analyses were carried out using the LogDet transformation to minimize the impact of nucleotide bias. These studies support the evolutionary relatedness of the Toxoplasma gondii rDNA with the large extrachromosomal rDNA of Plasmodium falciparum and with the organellar rDNA of another parasite in the phylum Apicomplexa, Babesia bovis. These analyses also suggest that the apicomplexan large extrachromosomal DNA may be more closely related to the plastid DNA of euglenoids than those of rhodophytes.

Animals↗

PubMed2001

Myosin diversity in Apicomplexa.

A polymerase chain reaction (PCR) screen was used to examine the diversity of myosins in 7 Apicomplexan parasites: Toxoplasma gondii, Plasmodium falciparum, Neospora caninum, Eimeria tenella, Sarcocystis muris, Babesia bovis, and Cryptosporidium parvum. Using degenerate PCR primers compatible with the majority of known myosin classes, putative myosin sequences were obtained from all of these species. All of the sequences obtained showed greatest similarity to previously identified apicomplexan myosins, suggesting that the diversity of myosins in these parasites is limited. Myosin classes that are known to be widespread across the phylogenetic spectrum, e.g., the myosins I, II, and V, were not seen in the Apicomplexa. Thus, like the plants, the Apicomplexa may have evolved their own unique cohort of myosins that are responsible for the myosin-driven cellular functions observed in these parasites.

Amino Acid Sequence↗

PubMed2004

Naiadocystis phykoterion n. gen., n. sp. (Apicomplexa: Eugregarinida: Hirmocystidae), from the Mexican pygmy grasshopper, Paratettix mexicanus (Orthoptera: Tetrigidae), in the Texas big thicket with recognition of three previously described species of Naiadocystis.

Naiadocystis phykoterion n. gen., n. sp. (Apicomplexa: Eugregarinida: Hirmocystidae), is described from the Mexican pygmy grasshopper, Paratettix mexicanus (Orthoptera: Tetrigidae), collected from sandbars along Harmon Creek, Walker County, Texas, in the western edge of the Texas Big Thicket. Naiadocystis n. gen. is distinguished by the form of the epimerite complex, a simple cordoid or toroid epimerite with an interior obconoid structure resembling a funnel that tapers to a distinct axial canal bisecting the protomerite, which is conspicuous in all stages of development, and a satellite protomerite reduced to a linearly crateriform cup or sucker that receives and enfolds posterior end of primite deutomerite. Association is precocious, caudofrontal, and biassociative. Gametocysts are spherical. Sporoducts are present but vestigial and irregular in number. Oocysts are broadly elliptoid with 4 small spherical polar knobs, 1 each at 30 degrees, 150 degrees, 210 degrees, and 330 degrees, and dehisce en masse. The species described herein are differentiated by their overall size and relative proportion of cellular structures. Naiadocystis acantholobae (Hoshide, 1952) n. comb., Naiadocystis acrydiinarum (Semans, 1939) n. comb., and Naiadocystis tetrigis (Corbel, 1968) n. comb. are recognized as members of Naiadocystis previously placed within Gregarina (Apicomplexa: Eugregarinida: Gregarinidae).

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