Experimental detection of the actinospores of Myxobolus pseudodispar (Myxosporea: Myxobolidae) in oligochaete alternate hosts

The development of Myxobolus pseudodispar Gorbunova, 1936, an intracellular myxosporean muscle parasite of the roach Rutilus rutilus L., was studied in experimentally infected oligochaetes. In one experiment, uninfected Tubifex tubifex Müller and Limnodrilus hoffmeisteri (Claparéde) were exposed to mature spores of M. pseudodispar. Triactinomyxon spores developed both in T. tubifex and L. hoffmeisteri specimens. Triactinospores were first released from the oligochaetes 76 d after initial exposure. At that time, pansporocysts containing 8 triactinospores were located in the gut epithelium of experimentally infected oligochaetes, but free actinosporean stages were also found in their gut lumen. Each triactinospore had 3 pyriform polar capsules and an elongated cylindrical sporoplasm with 8 secondary cells. The spore body joined the 3 caudal projections with a relatively long style. One of the 3 caudal projections was shorter than the other two. The total length of the triactinospore was on average 206.5 microns.     

The longevity of actinosporean spores from oligochaetes of Lake Sasajewun, Algonquin Park, Ontario, and their reaction to fish mucus

The longevity of 7 forms of actinosporean spores and the reaction of 6 forms of actinosporeans to fish mucus were investigated. The maximum longevity of actinosporean spores kept at ambient laboratory temperatures was 14 days. Spore longevity ranged from 11 to 14 days among actinosporeans. The reaction of spores to fish mucus varied among the actinosporeans. Triactinomyxon F of Xiao and Desser, 1998 reacted only to the mucus of the common shiner Luxilus cornutus, and golden shiner Notemigonus crysoleucas, whereas the aurantiactinomyxon form of Xiao and Desser, 1998, and raabeia B of Xiao and Desser, 1998 reacted readily to mucus of all fish species tested. The differences in reaction to fish mucus among actinosporeans may indicate their different host range. These results indicate that actinosporean spores are short-lived and that actinosporeans respond to their hosts by chemodetection.     

Structure and Development of a Marine Actinosporean, Sphaeractinomyxon ersei n. sp. (Myxozoa)

ABSTRACT This is the first ultrastructural study of the development of a marine actinosporean and of a species belonging to the genus Sphaeractinomyxon Caullery & Mesnil, 1904. S. ersei n. sp. is described from a limnodriloidine oligochaete, Doliodrilus diverticulatus Erséus, 1985, from Moreton Bay. Queensland, Australia. Development is asynchronous, there being all stages from two-celled pansporoblasts through to mature spores present simultaneously within a host. Spores develop in groups of eight within pansporoblasts in the coelom and when mature are located also in the intestinal lumen. The primordial spore envelope and sporoplasm develop separately in the pansporoblast until the polar filament is formed within the polar capsule and the capsulogenic cell cytoplasm has begun to degrade. The sporoplasm then enters the spore through a separated valve junction. Mature spores are triradially symmetrical with three centrally located polar capsules and a single binucleate sporoplasm with about 46 germ cells. Swellings or projections of the epispore do not occur when spores exit the host and contact sea water.     

放射孢子虫在中国的首次发现

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一种雷氏放射孢子虫的鉴定及其特征描述

放射孢子虫(Actinosporean)是黏体动物在其中间宿主水生无脊椎动物体内的一个生活阶段。研究鉴定并描述了一种雷氏放射孢子虫的形态和分子特征。该放射孢子虫的主要形态结构是: 由三个极囊、内含孢原质的孢子体和三个尾突组成, 无孢柄。极囊位于孢子体顶端, 呈梨形, 长5.2 μm, 宽2.9 μm; 孢子体侧面观呈长椭圆形, 长16.4 μm, 宽9.5 μm; 三个尾突基本等长, 呈锚状, 平均长度102.6 μm, 宽9.54 μm, 尾突末端轻微的上翘。每个尾突远侧端表面有许多形状不规则的棘状小刺。18S rDNA序列比对表明, 该雷氏放射孢子虫与国外已报道的Myxobolus cultus 18S rDNA序列一致性最高, 达98.41%, 由此推测该雷氏放射孢子虫可能为M. cultus的对应放射孢子虫阶段。研究丰富了国内放射孢子虫的基础研究。     

First record of an actinosporean (Myxozoa) in a marine polychaete annelid

The marine polychaete Nereis (Hediste) diversicolor (Annelida) from shallow water in the Oresund, Denmark, was found to be infected with an actinosporean stage of a myxozoan parasite. The body length of the pyriform actinospore is 12-16 microm and its maximum width is 10-12 microm. The spore is triangular in apical view, with the 3 spherical polar capsules distally. The spore is without caudal processes. Eight spores develop in each pansporocyst. Free spores and pansporocysts were found in the musculature and parapodia but not in the intestine. The myxosporean stage in fish is unknown. This is the first record of an actinosporean stage in a marine polychaete, but because marine oligochaetes are rare, compared with polychaetes, the latter are believed to play an important role as invertebrate (alternate) hosts in marine myxozoan life cycles.     

The pairing of nucleolar patterns in an epithelium as evidence for a conserved nuclear skeleton

The nucleoli in epidermal cells of fifth instar Calpodes and Manduca larvae undergo three cycles of unravelling into necklaces with condensation back to a dense particle or particles. Mitosis occurs before the first cycle and at the beginning of the third cycle. In spite of the formation and condensation of these nucleolar necklaces the nucleoli in the intercycle condition all have paired patterns. Adjacent pairs of nuclei have nucleoli that resemble one another in the number of their component particles, the shape and size of the particles and sometimes in their arrangement as mirror images. The paired patterns begin at mitosis and reform after necklace elongation and condensation. The patterns are presumed to reflect a nuclear skeleton that is paired from mitosis and conserved until the next mitosis. The nuclear pairing is related to the retention of mid bodies by sibling cells so that the epidermis is a collection of minimal two-cell syncytia.     

Immunohistochemical reactivity of polyclonal antibodies against Sphaerospora testicularis and Ceratomyxa labracis (Myxosporea: Bivalvulida), with other myxosporean parasites.

Immunological staining with rabbit antibodies raised against Sphaerospora testicularis and Ceratomyxa labracis was used to characterise their specificity and their reactivity towards other fish parasites. Polar capsules and valves of S. testicularis and C. labracis were labelled with their homologous antibody and cross reaction was observed with all the myxosporean parasites assayed from marine and freshwater fish hosts. All polar capsules were stained with both antibodies, except those of Zschokkella mugilis, which were not labelled with anti-S. testicularis serum. These observations suggest that polar capsules may be very conserved structures in myxosporean parasites from different hosts.     

Hungactinomyxon,a new actinosporean type and collective group(Myxozoa) from <Emphasis Type="Italic">Branchiura sowerbyi</Emphasis> Beddard (Oligochaeta)

Actinosporeans are characterised by great morphological diversity. As it has been proved that the class Actinosporea is a synonym of the Myxosporea, actinosporean genera have only been regarded only as actinosporean collective groups. While most actinosporeans are released individually by their oligochaete hosts, members of the synactinomyxon, siedleckiella and antonactinomyxon collective groups are released as eight connected structural elements. These actinosporean types are differentiated by the type of unit and junction of the caudal processes. On the basis of these characteristics, a new actinosporean type, constructed from eight echinactinomyxon units, is described as hungactinomyxon. Adjacent units are joined by two of their three processes and form two interconnected cubes, each containing four echinactinomyxons. Molecular biological studies also suggest that this new actinosporean type differs from other actinosporean types built up from eight structural elements for which 18S rDNA sequences are available in GenBank.     

Small Subunit Ribosomal RNA Sequences Unite Alternate Actinosporean and Myxosporean Stages of Myxobolus cerebralis the Causative Agent of Whirling Disease in Salmonid Fish

ABSTRACT. The alternating myxosporean and actinosporean stages of the myxozoan parasitc Myxobolus cerebralis (Hofer 1903) from its salmonid fish and aquatic oligochaete hosts, respectively, were compared for sequence homology of the small subunit (18S) ribosomal RNA genes. A 99.8% similarity between the sequences of these two stages was substantially greater than that of M. cerebralis compared to two other Myxobolus sp. from salmonid fish. Our results are the first molecular evidence confirming the alternating stages initially described by Wolf and Markiw [25] for the life cycle of M. cerebralis but found in two different taxonomic classes (Myxosporea and Actinosporea) are indeed forms of the same organism. Sequencing of rRNA genes of the actinosporean stage followed by development of specific primers for DNA amplification of the myxosporean stage, as in our study, should be applied to solve other myxozoan life cycles. Additionally, these approaches will in the future provide useful diagnostic reagents for the detection and study of this important group of fish pathogens.     

Development of the Polar Filament-Polaroplast Complex in a Microsporidian Parasite*

SYNOPSIS. The development of the polar filament in a microsporidian parasite was studied in the electron microscope. The polar filament is a peculiar and complex organelle with intricate anatomical relationships to other structures in the mature spore. The characteristic ultrastructure of the formative and mature stages of the polar filament made it possible to trace its development and study the interactions among various organelles during its formation. In sporoblasts the polar filament develops sequentially from 3 different regions. The base of the filament appears first and is derived from a dense body. The anterior part of the filament is formed from electron dense material located in the perinuclear cisterna and in agranular endoplasmic reticulum. The base and the anterior part of the filament move toward each other and fuse. Subsequently, the posterior part of the filament develops from the posterior part of the Golgi complex. The polar sac and the polaroplast surrounding the anterior segment of the filament are formed from the anterior region of the Golgi complex.     

Expression of prostasin serine protease and protease nexin-1 (PN-1) in rhesus monkey ovary during menstrual cycle and early pregnancy.

Serine proteases and their cognate serpin-class inhibitors are involved in the controlled proteolytic events during follicular development, ovulation, formation, and maintenance of the corpus luteum (CL). In this study, we investigated the expression patterns of prostasin serine protease and protease nexin-1 (PN-1), a serine protease inhibitor also called serpin-E2, in rhesus monkey ovaries during the menstrual cycle and early pregnancy, by using in situ hybridization and immunohistochemistry. Expression of prostasin was localized in oocyte, granulosa cells, and/or theca cells of early antral follicles and antral follicles, with high levels observed in preovulatory follicles. Prostasin was also localized at high levels of abundance in the CL during the menstrual cycle and early pregnancy. During the menstrual cycle, PN-1 was coordinately localized with prostasin in oocytes, granulosa cells, and theca cells of antral follicles and preovulatory follicles and in the CL. In addition, the PN-1 expression level in macaque CL during early pregnancy increased as pregnancy proceeded. We propose that prostasin may be involved in follicular development, ovulation, and CL formation, whereas PN-1 may be present to regulate the proteolysis in these processes.     

The formation of the pronuclei and their associated perinuclear cytoplasm; the determination of the phases of the first cleavage cycles in Crepidula fornicata (Mollusca,Gastropoda)

Summary

The behaviour of the male and the female pronuclei in Crepidula fornicata is studied, beginning at the formation of the second polar body. Shortly after the extrusion of the second polar body the female pronucleus is formed, and then the male pronucleus enters the yolk-free cytoplasm near the animal pole. Both pronuclei are enveloped by a typical nuclear membrane, and increase in size until the prophase; a zygote nucleus is not formed (“Ascaris type” of fertilization). In the meantime, the chromatin of both pronuclei is arranged in a meshwork in the centre of the pronuclei.

Shortly after the formation of the second polar body a special cytoplasm, the “perinuclear cytoplasm”, is formed in the vicinity of each of the pronuclei. During the early stages of the first cleavage cycle this cytoplasm is composed of numerous Golgi complexes, small dense Golgi vesicles, smooth endoplasmic reticulum vesicles, mitochondria and rosettes of glycogen-like granules. At later stages, when the pronuclei have met and their plasms coalesced, the number of Golgi elements decreases; at the same time, the small dense Golgi vesicles increase in number and aggregate in clusters.

The phases of the first three cleavage cycles are determined by cytophotometry. The nuclear DNA of the male pronucleus and that in the nuclei of the blastomeres of the 2- and the 4-cell stage is reduplicated between 7 and 33% of the normalized cleavage cycles; the G₂-phase is between 33 and 57%, while the mitotic phase occupies the last part of each cleavage cycle and the first 7% of the next cleavage cycle. There is no G j-phase. Since the female pronucleus lies just beneath the polar bodies, its DNA content could not be measured separately.     

Subcellular Localization of Bacillus subtilis SMC, a Protein Involved in Chromosome Condensation and Segregation

We have investigated the subcellular localization of the SMC protein in the gram-positive bacterium Bacillus subtilis. Recent work has shown that SMC is required for chromosome condensation and faithful chromosome segregation during the B. subtilis cell cycle. Using antibodies against SMC and fluorescence microscopy, we have shown that SMC is associated with the chromosome but is also present in discrete foci near the poles of the cell. DNase treatment of permeabilized cells disrupted the association of SMC with the chromosome but not with the polar foci. The use of a truncated smc gene demonstrated that the C-terminal domain of the protein is required for chromosomal binding but not for the formation of polar foci. Regular arrays of SMC-containing foci were still present between nucleoids along the length of aseptate filaments generated by depleting cells of the cell division protein FtsZ, indicating that the formation of polar foci does not require the formation of septal structures. In slowly growing cells, which have only one or two chromosomes, SMC foci were principally observed early in the cell cycle, prior to or coincident with chromosome segregation. Cell cycle-dependent release of stored SMC from polar foci may mediate segregation by condensation of chromosomes.     

Molecular characterization of myxozoan parasites from Lake Sasajewun, Algonquin Park, Ontario, by riboprinting

The small subunit-rRNA genes of 18 myxozoans from Lake Sasajewun, Algonquin Park were amplified and digested with restriction endonucleases for riboprinting analysis. Identical riboprints were not found between the myxosporeans and the actinosporeans. The distinct riboprinting patterns observed among these myxozoans indicate considerable genetic diversity within this group. Identical riboprints were found between Myxobolus pendula and Myxobolus pellicides, and between triactinomyxon 'C' and Triactinomyxon ignotum. Parsimony analysis of the riboprints demonstrated that neither the myxosporeans nor the actinosporeans formed a monophyletic group. Some species of Myxobolus are more closely related to forms of triactinomyxon, echinactinomyxon or raabeia than to other Myxobolus species. These results are consistent with the two-host life cycle hypothesis of myxozoans that myxosporeans and actinosporeans are alternating stages of the same organisms.     

Boron controls suspensor development in embryogenic cultures of Larix decidua

Suspensor formation in somatic embryos of Larix decidua Mill. was. studied in relation to its dependence on nutritional factors of the culture medium. Protoplasts exhibiting embryogenic competence were prepared from an embryogenic suspension culture, immobilized in Ca-alginate and cultured in liquid media. Developmental patterns showed qualitative differences in the two basic media used. In one medium, containing 100 μ M boric and, compact colonies developed, most of which displayed formation of polar suspensors after 3 to 4 weeks. In contrast, suspensor development never occurred in the other medium, containing 10 μ M borate, yet colonies of loosely connected cytoplasmically dense cells were regenerated without loss of embryogenic competence. Detailed examination of the constituents of the two media led to the conclusion that suspensor development is dependent on boron concentration: below 35 μ M boron, suspensor formation is blocked completely, whereas with an increase up to 1 μ M boron there is a progressively faster development of suspensor-bearing embryos.     

Small subunit ribosomal RNA sequence of Henneguya exilis (class Myxosporea) identifies the actinosporean stage from an oligochaete host

Several transmission studies, as well as recent molecular data, have indicated that the two classes Myxosporea and Actinosporea represent different life cycle stages of Myxozoa. To evaluate the life cycles of myxozoa in catfish aquaculture systems, the small subunit (18S) ribosomal RNA gene sequences of Henneguya exilis, a myxosporean from channel catfish Ictalurus punctatus, and an actinosporean (previously designated as Aurantiactinomyxon janiszewskai) from the aquatic oligochaete Dero digitata were determined. The sequences were identical, indicating that H. exilis and the actinosporean are alternate life stages of a single species. This is the first report identifying the actinosporean stage of the genus Henneguya.     

On the significance of alternating patterns of polar and non-polar residues in beta-strands

A common assumption about protein sequences in beta-strands is that they have alternating patterns of polar and non-polar residues. It is thought that such patterns reflect the interior/exterior geometry of amino acid residue side-chains on a beta-sheet. Here we study the prevalence of simple hydrophobicity patterns in parallel and antiparallel beta-sheets in proteins of known structure and in the sequences of amyloidogenic proteins. The occurrence of 32 possible pentapeptide binary patterns (polar (P)/non-polar (N)) is computed in 1911 non-homologous protein structures. Despite their tendency to aggregate in experimentally designed proteins, the purely alternating hydrophobic/polar patterns (PNPNP and NPNPN) are most frequent in beta-sheets, typically occurring in antiparallel strands. The overall distribution of the pentapeptide binary patterns is significantly different in strands within parallel and antiparallel sheets. In both types of sheets, complementary patterns (where the hydrophobic and polar residues pair with one another) associate preferentially. We do not find alternating patterns to be common in amyloidogenic proteins or in short fragments involved directly in amyloid formation. However, we do note some similarities between patterns present in amyloidogenic sequences and those in parallel strands.