Multinucleate Plasmodia Research Articles

Haplosporidium acetes n. sp. infecting the hepatopancreas of jelly prawns Acetes sibogae australis from Moreton Bay, Australia

Wild Acetes sibogae australis from northern Moreton Bay, Australia displaying opacity of the hepatopancreas were sampled and examined histologically, revealing infection by multinucleate plasmodia of a haplosporidian-like parasite in the epithelial cells of the hepatopancreas. A morphological and phylogenetic investigation identified the parasite as a novel species of the order Haplosporida, and the parasite is described as Haplosporidium acetes n. sp. This is the first report of disease caused by a haplosporidian in wild Australian decapod crustaceans, and the first record of haplosporidiosis in sergestid shrimp. Infections of H. acetes were observed in all cell types (R, B, F and E) within the hepatopancreas. Infected epithelial cells became hypertrophied as they filled with haplosporidian parasites and, in heavy infections, caused almost complete displacement of normal hepatopancreas tissue. Although sporulation was not observed, infected jelly prawns appeared terminally diseased. Infections became grossly evident in around 5% of wild prawns during early autumn at a time of year when jelly prawn populations decline rapidly with decreasing water temperatures, however histopathology indicated at least 13% of apparently normal jelly prawns were also infected. Further studies are required in order to determine if this parasite influences jelly prawn population dynamics. In addition, we report co-infection of a novel microsporidian parasite in the Enterocytozoon Group Microsporidia (EGM) infecting nuclei of hepatopancreatic epithelial cells. The microsporidian was phylogenetically distinct from Enterocytozoon hepatopenaei (EHP) known to infect penaeid shrimp in Asia.

New insights about Haplosporidium pinnae and the pen shell Pinna nobilis mass mortality events

Since early autumn 2016, Mass Mortality Events (MME) have drastically impacted the population of the fan mussel Pinna nobilis in the Mediterranean Sea. Haplosporidium pinnae, a newly described Haplosporidian species, has been considered the causative agent of the mortality outbreaks in association to opportunistic bacterial pathogens. In the present study, we first reported a cytological description of H. pinnae in moribund specimens of P. nobilis which were collected in the Gulf of Taranto (Ionian Sea, Italy) during summer 2018. Different life-cycle stages of the parasite, including uni- and binucleate cells, small plasmodia, big multinucleate plasmodia and sporocysts with spores, were detected in all the examined animals and most of the parasite cells were present in gills, mantle and digestive gland, while the spores were found only in the latter organ. Histology and molecular biology were also performed, confirming the nature of the infectious agent, as already reported in the area. Additionally, molecular study revealed the presence of bacteria from the Mycobacterium ulcerans - M. marinum complex but no evident macroscopical or microscopical lesions, just as no bacteria referred to Mycobacterium were observed by histology. In conclusion, the present study aimed to provide further contributions to the understanding of the mortality of P. nobilis, pointing to the role of the cytological method of investigation both for diagnostic and epidemiological purposes, and discussing the current epidemic situation in the Adriatic sea.

Enterocytozoon bieneusi

Enterocytozoon bieneusi is a microsporidium, related to Cryptomycota and fungi, which has been reported globally in a wide range of mammalian and avian hosts. It is responsible for over 90% of documented cases of human microsporidiosis and causes varying clinical symptoms, typically diarrhea and wasting. Infection begins with ingestion of spores in contaminated water and food. Spores deliver the infective sporoplasm into host enterocytes via the discharged polar tube. Meronts form and develop into multinucleated plasmodia, which undergo sporogony to form sporoblasts and then mature spores. Spores released from infected cells are shed with the stool. Sequence analysis of the ribosomal internal transcribed spacer (ITS) has identified over 500 genotypes, some of which are generalists of zoonotic importance and pose a threat to public health. Population genetic data uphold the zoonotic nature and host specificity of the parasite. Knowledge of its pathogenicity, immune responses, and expanded treatment options are urgently needed.

Expression and localization of adreno-corticotropic-hormone (ACTH) and NeuN in myxomycete plasmodia

The myxomycete life-cycle mainly consists of cellular uninucleate amoeboflagellates, stationary spore-bearing sporophores, and acellular multinucleate plasmodia. The plasmodium is able to regulate complex behavior, but no differentiated signaling structures have been detected. As a basal lineage eukaryote, research on any neuron-like substances may contribute to our understanding of the origin of the nervous system in complex organisms. We examined the expression and localization of the neuropeptide adreno-cortico-tropic-hormone (ACTH) and the neuroprokaryotic protein (NeuN) in two species of Physarum under different culture conditions were studied by immunofluorescence and western blotting. ACTH was expressed in the cytoplasm of the plasmodium of Physarum flavicomum, and NeuN was expressed in the nuclear membrane of the plasmodium of P. polycephalum and in the cytoplasm of that of P. flavicomum. This demonstrates the occurrence of neuropeptides in the myxomycete plasmodium for the first time and contributes to the understanding of intercellular communication in Myxomycetes.

Temporal dynamics of infection of cockles Cerastoderma edule with the protistan parasite Minchinia tapetis (Rhizaria: Haplosporida) in Galicia (NW Spain)

Uninucleate and binucleate cells and multinucleate plasmodia of a haplosporidan-like protist associated with heavy haemocytic infiltration were observed in histological sections of cockles, Cerastoderma edule, from the Ría de Noia (Galicia, NW Spain) in the course of a cockle health surveillance programme. Molecular assays provided identification of this protist as Minchinia tapetis, which we thus record from a new host. Prevalence of M. tapetis as high as 93% was recorded but infection intensity was low to moderate, never heavy, and abnormally high cockle mortality was not observed in the ria by shellfishers. A significant positive correlation was found between M. tapetis prevalence and sea water temperature. Sea water temperature increase associated with climate change might contribute to increase the prevalence of this infection in cockles and, as a consequence, this parasite may be considered a threat for cockle production.

Life Cycles of Myxogastria Stemonitopsis typhina and Stemonitis fusca on Agar Culture.

Myxogastria is a group of protozoa characterized by cellular uninucleate amoeboflagellates (myxamoebae and flagellated swarm cell), acellular multinucleate plasmodia, and stationary spore‐bearing sporocarps. The Stemonitales is a large order in the Myxogastria and contains approximately 230 species, but only 13 species have their completed life cycles observed so far. Here, we described the life cycles of two species in Stemonitales, Stemonitopsis typhina and Stemonitis fusca by culturing in water agar medium and observing the morphogenesis of their spore germination, plasmodium, and sporocarp development. The spore‐to‐spore life cycles of Ste. typhina and S. fusca were completed in approximately 67 and 12 d, respectively. Both species possessed an aphanoplasmodium. However, the spores of Ste. typhina and S. fusca germinated by the V‐shape split and pore methods, respectively. Unlike S. fusca with an evanescent peridium, Ste. typhina produced a shiny persistent peridium which was continuous with the membrane surrounding its stalk. The information will contribute to a better understanding of their taxonomy and phylogeny.

Zoological terms in the human histological nomenclature Terminologia Histologica. What we think, what we know, and what we think we know

Terminology in morphological and zoological sciences is enormously important. Proper denomination of individual structures of the animal / human body from the microscopic point of view has an irreplaceable role in unambiguous understanding and communication among scientists regardless of their field of expertise. The year 2008 can be considered a crucial year in the developing of internationally accepted histological terminology, because it was the year when the first internationally renowned human histology nomenclature Terminologia Histologica was published. The current version of the Terminologia Histologica contains also the description of many microscopic organs and structures whose presence in different animal species is widely accepted, however their presence in humans is disputable. Typical examples are the haemal lymph nodes and haemal nodes, mentioned in the chapter Lymphoid organs which are secondary lymphoid organs found in many different mammalian species, but also in some birds. They are capable of performing haematopoietic and immunological functions but in the absence of lymphatic system pathology, no structures resembling haemal nodes / haemal lymph nodes have been detected in humans. Neurohaemal organs are mentioned within the chapter Endocrine system. Neurohaemal organs are known by different names, depending on the animal species studied, e.g. corpora allata or abdominal perisympathetic organs. To this date, these structures have been described in many different invertebrate species, but neurohaemal organs are also found in some lower vertebrates, in which the neurohaemal organ is referred to as “urophysis”. According to our opinion, structures called neurohaemal organs in invertebrates are counterparts to circumventricular organs found in vertebrates, but cannot be named as such. Another somewhat controversial term mentioned in human histological nomenclature is the vomeronasal organ mentioned in the chapter Respiratory system. It is a specialized organ, which forms an integral supportive part of the olfaction of many mammalian species and reptiles. It is believed that the main function of vomeronasal organ is to regulate various behavioral aspects of intraspecies interaction by facilitating the detection of pheromones. The function and even existence of the vomeronasal organ in humans is a source of significant dispute among researchers. Some of them stated that vomeronasal organ disappears during fetal development, with except the vomeronasal duct. On the other hand, there are also authors who concluded that the vomeronasal organ is definitely present in adult humans. Similarly disputable question is the presence of multinucleated plasmodia in human body. This opinion article aims to open a wide scientific discussion concerning the importance and aptness of the inclusion of these terms in the human histological nomenclature despite they are probably exclusively zoological.

Histological analysis of an outbreak of red gill disease in cultured oriental river prawn Macrobrachium nipponense

An epidemic of red gill disease with a high mortality rate recently occurred in the cultured oriental river prawn Macrobrachium nipponense in China. The prawns had flaccid bodies and gills were red in color with numerous black spots. By wet smear microscopy and negative staining, numerous membrane-bound plasmodia or degenerated spores were observed. Histological sections indicated the infection was limited to the gills. The gill filaments were filled with masses of mononuclear parasites, multinucleate and multicellular plasmodia and became enormously hypertrophic. Host encapsulation response and inflammatory foci with phagocytized parasite spores were evident. Transmission electron microscopy (TEM) analysis confirmed the gross plasmodia almost filling the entire space of gill epithelial cell. The intracellular parasite was a multinucleate plasmodium enclosed in a vacuole within the cytoplasm of the host cell. Large numbers of trophonts were visible in each plasmodium. High degree of vesiculation of early sporonts was evident. Scanning electron microscopy (SEM) and TEM observations all revealed characteristic tubular extension from the surface of a late sporont. We recognized the risk of associating the presence of a parasite with a particular pathology in the absence of total evidence that demonstrates an unequivocal link between the parasite, the perceived pathology and a clear disease manifestation that would be demonstrated by e.g. experimental studies. However, given the widespread importance of the host in aquaculture, it is necessary to provide this short report to highlight to other researchers and to the industry the potential for a new and emerging disease. It is hoped that this will lead to additional sightings of the condition and additional research to confirm the link between parasite and the pathology seen. It is our intention to complete life-cycle studies with to satisfy Koch's postulate.

Pseudokabatana alburnus n. gen. n. sp., (Microsporidia) from the liver of topmouth culter Culter alburnus (Actinopterygii, Cyprinidae) from China.

We describe the type species of a novel genus of microsporidian parasite, Pseudokabatana alburnus n. gen. n. sp., infecting the liver of topmouth culter, Culter alburnus Basilewsky, 1855, from Lake Poyang off Xingzi county, Jiangxi Province, China. The parasite elicits formation of spherical xenomas of up to 1.2mm in diameter containing all observed life stages from early merogonal plasmodia to mature spores contained within the cytoplasm of host hepatocytes. Merogonal plasmodia existed in direct contact with the host cytoplasm and contained up to 20 visible nuclei. Plasmotomy of the multinucleate plasmodium led to formation of uninucleate cells in which the nucleus underwent further division to form bi-nucleate presporonts, sporonts (defined by cells with a thickened endospore) and eventually sporoblasts (containing pre-cursors of the spore extrusion apparatus). Mature spores were pyriform and monokaryotic, measuring 2.3 ± 0.19μm long and 1.3 ± 0.10μm wide. Spores possessed a bipartite polaroplast and 5-6 coils of a polar filament, in a single rank. The obtained partial SSU rRNA gene sequence, 1383bp in length, did not match any of microsporidia available in GenBank. SSU rDNA-based phylogenetic analysis indicated a new taxon branching with Kabatana rondoni, a parasite infecting the skeletal muscle of Gymnorhamphichthys rondoni from the Amazon River. Due to different host and tissue tropism, the novel taxon did not fit the diagnostic criteria for the genus Kabatana. Further, based on SSU rDNA-inferred phylogenetic analyses, different ultrastructural features of developmental stages, and ecological considerations, a new genus Pseudokabatana and type species Pseudokabatana alburnus n. sp. was erected for the parasite in topmouth culter.

Haplosporidium pinnae sp. nov., a haplosporidan parasite associated with mass mortalities of the fan mussel, Pinna nobilis, in the Western Mediterranean Sea.

This study provides morphological and molecular characterization of a new species, Haplosporidium pinnae), very likely responsible for mass mortality of fan mussels, Pinna nobilis, in the Western Mediterranean Sea. The parasite was found in dead or moribund P. nobilis but did not occur in healthy fan mussels from locations that were not affected by abnormal mortality. Histological examination of infected fan mussels showed uninucleate cells of a haplosporidan parasite throughout the connective tissue and hemolymph sinuses of the visceral mass and binucleate cells and, rarely, multinucleate plasmodia were also detected in the connective tissue. Additionally, stages of sporulation occurred in the epithelium of the host digestive gland tubules. Spores were slightly ellipsoidal with a hinged operculum in one pole. Typical haplosporosomes were not found with TEM but vesicles with two concentric membranes resembling haplosporosomes were abundant in the cytoplasm of the multinucleate plasmodia occurring in host digestive gland tubules. SEM analysis showed multiple structures on the spore surface; some spores had two or four long tape-like filaments attached to the spore wall. Phylogenetic analysis based on the SSU rDNA sequence placed this parasite within a large clade including species of the order Haplosporida, not in the Bonamia/Minchinia subclade or the subclade containing most Haplosporidium species, but within a subclade of Haplosporidium sp. from Penaeus vannamei. Our results suggested that H. pinnae and the parasite of P. vannamei may represent a distinct new genus within the order Haplosporida.

A Minchinia mercenariae-like parasite infects cockles Cerastoderma edule in Galicia (NW Spain).

The cockle Cerastoderma edule fishery has traditionally been the most important shellfish species in terms of biomass in Galicia (NW Spain). In the course of a survey of the histopathological conditions affecting this species in the Ria of Arousa, a haplosporidan parasite that had not been observed in Galicia was detected in one of the most productive cockle beds of Galicia. Uni- and binucleate cells and multinucleate plasmodia were observed in the connective tissue mainly in the digestive area, gills and gonad. The parasite showed low prevalence, and it was not associated with abnormal cockle mortality. Molecular identification showed that this parasite was closely related to the haplosporidan Minchinia mercenariae that had been reported infecting hard clams Mercenaria mercenaria from the Atlantic coast of the United States. The molecular characterization of its SSU rDNA region allowed obtaining a fragment of 1,796bp showing 98% homology with M.mercenariae parasite. Phylogenetic analysis supported this identification as this parasite was clustered in the same clade as M.mercenariae from the United States and other M.mercenariae-like sequences from the UK, with bootstrap value of 99%. The occurrence of M.mercenariae-like parasites infecting molluscs outside the United States is confirmed.

Morphologic and molecular data help adopting the insect-pathogenic nephridiophagids (Nephridiophagidae) among the early diverging fungal lineages, close to the Chytridiomycota

Nephridiophagids are poorly known unicellular eukaryotes, previously of uncertain systematic position, that parasitize the Malpighian tubules of insects. Their life cycle includes merogony with multinucleate plasmodia and sporogony leading to small, uninucleate spores. We examined the phylogenetic affiliations of three species of Nephridiophaga, including one new species, Nephridiophaga maderae, from the Madeira cockroach (Leucophaea maderae). In addition to the specific host, the new species differs from those already known by the size of the spores and by the number of spores within the sporogenic plasmodium. The inferred phylogenetic analyses strongly support a placement of the nephridiophagids in the fungal kingdom near its root and with a close, but unresolved, relationship to the chytids (Chytridiomycota). We found evidence for the nephridiophagidean speciation as being strongly coupled to host speciation.

Ultrastructural characterization of Pleistophora macrozoarcidis Nigerelli 1946 (Microsporidia) infecting the ocean pout Macrozoarces americanus (Perciformes, Zoarcidae) from the gulf of Maine, MA, USA.

Pleistophora macrozoarcidis a microsporidian parasite infecting the muscle tissue of the ocean pout Macrozoarces americanus collected from the Gulf of Maine of the Atlantic Ocean, MA, USA, was morphologically described on the basis of ultrastructural features. Infection was detected as opaque white or rusty brown lesions scattered throughout the musculature of the fish mainly in the region anterior to anus. Transmission electron microscopy showed that in individual parasitized muscle cells, the infection progresses within parasite formed vesicles which are in direct contact with muscle cell elements. The earliest observed parasitic stages are the globular multinucleated proliferative cells or plasmodia limited by a highly tortuous plasmalemma with intervesicular finger-like digitations projecting into the parasite cytoplasm. These cells divided through the invagination of the plasmalemma and the amorphous coat producing daughter-cells. Fine electron-dense secretion is deposited on the plasmalemma that causes its thickening which is a sign of commencement of the sporogonic phase. This phase is carried out by cytokinesis of the sporonts and results in the formation of sporoblasts and finally spores. Mature spore has a thin electron-dense exospore, a thick electron-lucent endospore, and the plasma membrane which encloses the spore contents. A single nucleus is centrally located with the posterior region containing a posterior vacuole. The majority of spores have 7-13 coils in 1-2 rows, and a small group of spores had about 23 coils forming two rows. Events of polar filament extrusion for penetration of uninfected cells were studied. The polaroplast membranes were expanded and occupy most of the length of the spore. The coils are dislocated from the sides of the spore to throughout the entire sporoplasm. The polar filament everts and extrudes through the polar cap with a sufficient force to pierce adjacent sporophorous vesicle walls. After eversion, the polar filament is referred to as a polar tubule, as it forms a tube through which the sporoplasm travels. It pierces anything in its path and deposits the sporoplasm at a new location to begin another infective cycle.

The Genome of Intoshia linei Affirms Orthonectids as Highly Simplified Spiralians

Orthonectids are rare parasites of marine invertebrates [1] that are commonly treated in textbooks asa taxon of uncertain affinity [2]. Trophic forms of orthonectids reside in the tissues of their hosts as multinucleated plasmodia, generating short-lived, worm-like ciliated female and male organisms that exit into the environment for copulation [3]. These ephemeral males and females are composed of just several hundred somatic cells and are deprived of digestive, circulatory, or excretory systems. Since their discovery in the 19(th) century, the orthonectids were described as organisms with no differentiated cell types and considered as part of Mesozoa, a putative link between multicellular animals and their unicellular relatives. More recently, this view was challenged as the new data suggested that orthonectids are animals that became simplified due to their parasitic way of life [3, 4]. Here, we report the genomic sequence of Intoshia linei, one of about 20 known species of orthonectids. The genomic data confirm recent morphological analysis asserting that orthonectids are members of Spiralia and possess muscular and nervous systems [5]. The 43-Mbp genome of I.linei encodes about 9,000 genes and retains those essential for the development and activity of muscular and nervous systems. The simplification of orthonectid body plan is associated with considerable reduction of metazoan developmental genes, leaving what might be viewed as the minimal gene set necessary to retain critical bilaterian features.

Species-specific cell mobility of bacteria-feeding myxamoebae in plasmodial slime molds

On decaying wood or litter in forests, plasmodial slime molds (myxomycetes) represent a large fraction of eukaryotic protists that feed on bacteria. In his seminal book Experimental Physiology of Plants (1865), Julius Sachs referred to the multinucleate plasmodium of myxomycetes, which were considered at that time as primitive plants (or fungi). Today it is well established that myxomycetes are members of the Amoebozoa (Protista). In this study we compare the mobility of myxamoebae of 3 European species, Lycogala epidendrum (order Liceales), Tubulifera arachnoidea, and Trichia decipiens (order Trichiales). Using agar plates, on which 3 separate bacterial species were cultivated as prey organisms (Methylobacterium mesophilicum, Escherichia coli, Agrobacterium tumefaciens), we document large differences in cell motility between the myxomycetes investigated. In addition, we show that the 3 species of myxamoebae can be distinguished based on their average cell size. These data shed light on the mode of co-occurrence via differential substrate utilization in these members of the Amoebozoa.

Spermatogenesis and auxospore structure in the multipolar centric diatom Hydrosera.

Spermatogenesis and auxospore development were studied in the freshwater centric diatom Hydrosera triquetra. Spermatogenesis was unusual, lacking depauperating cell divisions within the spermatogonangium. Instead, a series of mitoses occurred within an undivided cell to produce a multinucleate plasmodium with peripheral nuclei, which then underwent meiosis. 32 or 64 sperm budded off from the plasmodium leaving a large residual cell containing all the chloroplasts. Similar development apparently occurs in Pleurosira, Aulacodiscus, and Guinardia, these being so distantly related that independent evolution of plasmodial spermatogenesis seems likely. After presumed fertilization, the Hydrosera egg cell expanded distally to form a triangular end part. However, unlike in other triangular diatoms (Lithodesmium, Triceratium), the development of triradiate symmetry was not controlled by the "canonical" method of a perizonium that constrains expansion to small terminal areas of the auxospore wall. Instead, the auxospore wall lacked a perizonium and possessed only scales and a dense mat of thin, apparently entangled strips of imperforate silica. No such structures have been reported from any other centric diatoms, the closest analogs being instead the incunabular strips of some raphid diatoms (Nitzschia and Pinnularia). Whether these silica structures are formed by the normal method (intracellular deposition within a silica deposition vesicle) is unknown. As well as being more rounded than vegetative cells, the initial cell is aberrant in its structure, since it has a less polarized distribution of the "triptych" pores characteristic of the species.

A novel phytomyxean parasite associated with galls on the bull-kelp Durvillaea antarctica (Chamisso) Hariot.

Durvillaea antarctica (Fucales, Phaeophyceae) is a large kelp of high ecological and economic significance in the Southern Hemisphere. In natural beds along the central coast of Chile (Pacific Ocean), abnormal growth characterized by evident gall development and discolorations of the fronds/thallus was observed. Analysing these galls by light microscopy and scanning electron microscopy revealed the presence of endophytic eukaryotes showing typical characteristics for phytomyxean parasites. The parasite developed within enlarged cells of the subcortical tissue of the host. Multinucleate plasmodia developed into many, single resting spores. The affiliation of this parasite to the Phytomyxea (Rhizaria) was supported by 18S rDNA data, placing it within the Phagomyxida. Similar microorganisms were already reported once 23 years ago, indicating that these parasites are persistent and widespread in D. antarctica beds for long times. The symptoms caused by this parasite are discussed along with the ecological and economic consequences. Phytomyxean parasites may play an important role in the marine ecosystem, but they remain understudied in this environment. Our results demonstrate for the first time the presence of resting spores in Phagomyxida, an order in which resting spores were thought to be absent making this the first record of a phagomyxean parasite with a complete life cycle so far, challenging the existing taxonomic concepts within the Phytomyxea. The importance of the here described resting spores for the survival and ecology of the phagomyxid parasite will be discussed together with the impact this parasite may have on ‘the strongest seaweed of the world’, which is an important habitat forming and economic resource from the Southern Hemisphere.

A haplosporidian parasite associated with high mortality and slow growth in Penaeus (Litopenaeus) vannamei cultured in Indonesia

High mortality of juvenile Penaeus (Litopenaeus) vannamei less than one month old in Indonesia has been observed in shrimp farms and hatcheries since 2007. The gross signs of disease included shrinkage of the hepatopancreas, flaccid bodies, cuticular melanization and retarded growth. Overall loss in the severely-infected farms was 60 to 90% due to progressive mortality. The loss since 2007 is estimated to be more than 5millionUSdollars. PCR testing of shrimp samples for major viral pathogens gave negative results, but histopathological analysis of hepatopancreatic (HP) tissue showed evidence of a haplosporidian parasite indicated by cytoplasmic multinucleate plasmodia and trophonts in tubule epithelial cells. Plasmodia caused disruption of HP tubule epithelial cells when they discharged trophonts into the tubular lumen. To confirm the presence of haplosporidia, PCR was performed to amplify a small subunit rRNA gene (SSU rDNA) fragment and a cloned 1.5kb amplicon showed 96% sequence identity to that of a haplosporidian previously described in P. vannamei from Belize, Central America suggesting that the Indonesian haplosporidian was either conspecific or very closely related. In situ hybridization assays using a probe based on this amplicon gave positive results specifically with the putative haplosporidian lesions. Prevalence of infections in broodstock and ponds from 2004 to 2010 suggested that the haplosporidian disease outbreaks had resulted from stocking of infected post-larvae.

Futile attempts to differentiate provide molecular evidence for individual differences within a population of cells during cellular reprogramming

The heterogeneity of cell populations and the influence of stochastic noise might be important issues for the molecular analysis of cellular reprogramming at the system level. Here, we show that in Physarum polycephalum, the expression patterns of marker genes correlate with the fate decision of individual multinucleate plasmodial cells that had been exposed to a differentiation-inducing photostimulus. For several hours after stimulation, the expression kinetics of PI-3-kinase, piwi, and pumilio orthologs and other marker genes were qualitatively similar in all stimulated cells but quantitatively different in those cells that subsequently maintained their proliferative potential and failed to differentiate accordingly. The results suggest that the population of nuclei in an individual plasmodium behaves synchronously in terms of gene regulation to an extent that the plasmodium provides a source for macroscopic amounts of homogeneous single-cell material for analysing the dynamic processes of cellular reprogramming. Based on the experimental findings, we predict that circuits with switch-like behaviour that control the cell fate decision of a multinucleate plasmodium operate through continuous changes in the concentration of cellular regulators because the nuclear population suspended in a large cytoplasmic volume damps stochastic noise.

The cell structure of the reticulopodial amoeba Filoreta marina Bass et Cavalier-Smith (Cercozoa)

The cell structure of a reticulopodial amoeba, Filoreta marina Bass et Cavalier-Smith, is described. The cell is covered by a unitary membrane; glycostyles are absent. The life cycle comprises the uninucleate stage, multinucleate plasmodium, and spherical uninucleate cysts. The microtubules inside pseudopodia and the flagella are absent. The vesicular nuclei, endoplasmic reticulum, and Golgi apparatus are of a typical structure. The plasmodium produces a branched network of narrow anastomosing (reticulopodia) and wide pseudopodia. Thin unbranched micropseudopodia have also been observed. Oval mitochondria with a size of 0.3 × 0.6 μm contain the tubular cristae. A bidirectional motion of the cytoplasm inside the reticulopodia has been detected. Extrusomes (extrusive organelles) have not been found. The contractile vacuole is absent. F. marina feeds on bacteria. A similarity of this amoeba to other filose and reticulopodial amoebas is discussed.