A myxozoan genome reveals mosaic evolution in a parasitic cnidarian.

BACKGROUND: Parasite evolution has been conceptualized as a process of genetic loss and simplification. Contrary to this model, there is evidence of expansion and conservation of gene families related to essential functions of parasitism in some parasite genomes, reminiscent of widespread mosaic evolution-where subregions of a genome have different rates of evolutionary change. We found evidence of mosaic genome evolution in the cnidarian Myxobolus honghuensis, a myxozoan parasite of fish, with extremely simple morphology. RESULTS: We compared M. honghuensis with other myxozoans and free-living cnidarians, and determined that it has a relatively larger myxozoan genome (206 Mb), which is less reduced and less compact due to gene retention, large introns, transposon insertion, but not polyploidy. Relative to other metazoans, the M. honghuensis genome is depleted of neural genes and has only the simplest animal immune components. Conversely, it has relatively more genes involved in stress resistance, tissue invasion, energy metabolism, and cellular processes compared to other myxozoans and free-living cnidarians. We postulate that the expansion of these gene families is the result of evolutionary adaptations to endoparasitism. M. honghuensis retains genes found in free-living Cnidaria, including a reduced nervous system, myogenic components, ANTP class Homeobox genes, and components of the Wnt and Hedgehog pathways. CONCLUSIONS: Our analyses suggest that the M. honghuensis genome evolved as a mosaic of conservative, divergent, depleted, and enhanced genes and pathways. These findings illustrate that myxozoans are not as genetically simple as previously regarded, and the evolution of some myxozoans is driven by both genomic streamlining and expansion.

Transcriptomic Insights into the Diversity and Evolution of Myxozoa (Cnidaria, Endocnidozoa) Toxin-like Proteins.

Myxozoa is a speciose group of endoparasitic cnidarians that can cause severe ecological and economic effects. Their cnidarian affinity is affirmed by genetic relatedness and the presence of nematocysts, historically called "polar capsules". Previous studies have revealed the presence of toxin-like proteins in myxozoans; however, the diversity and evolution of venom in Myxozoa are not fully understood. Here, we performed a comparative analysis using the newly sequenced transcriptomes of five Myxobolidae species as well as some public datasets. Toxin mining revealed that myxozoans have lost most of their toxin families, while most species retained Kunitz, M12B, and CRISP, which may play a role in endoparasitism. The venom composition of Endocnidozoa (Myxozoa + Polypodium) differs from that of free-living cnidarians and may be influenced by ecological and environmental factors. Phylogenetic analyses showed that toxin families of myxozoans and free-living cnidarians were clustered into different clades. Selection analyses showed that purifying selection was the dominant evolutionary pressure in toxins, while they were still influenced by episodic adaptive selection. This suggests that the potency or specificity of a particular toxin or species might increase. Overall, our findings provide a more comprehensive framework for understanding the diversity and evolution of Myxozoa venoms.

Controllable coupling between an ultra-high-Q microtoroid cavity and a graphene monolayer for optical filtering and switching applications.

Whispering-gallery-mode optical microresonators have found impactful applications in various areas due to their remarkable properties such as ultra-high quality factor (Q-factor), small mode volume, and strong evanescent field. Among these applications, controllable tuning of the optical Q-factor is vital for on-chip optical modulation and various opto-electronic devices. Here, we report an experimental demonstration with a hybrid structure formed by an ultra-high-Q microtoroid cavity and a graphene monolayer. Thanks to the strong interaction of the evanescent wave with the graphene, the structure allows the Q-factor to be controllably varied in the range of 3.9 × 105 ∼ 6.2 × 107 by engineering optical absorption via changing the gap distance in between. At the same time, a resonant wavelength shift of 32 pm was also observed. Besides, the scheme enables us to approach the critical coupling with a coupling depth of 99.6%. As potential applications in integrated opto-electronic devices, we further use the system to realize a tunable optical filter with tunable bandwidth from 116.5 MHz to 2.2 GHz as well as an optical switch with a maximal extinction ratio of 31 dB and response time of 21 ms.

A fast and effective method for dissecting parasitic spores: myxozoans as an example.

Disassembling the parasitic spores and acquiring the main subunits is a prerequisite for deep understanding of the basic biology of parasites. Herein we present a fast and efficient method to dissect the myxospores in a few steps, which mainly involved sonication, sucrose density gradient and Percoll density gradient. We tested our method on three myxozoans species and demonstrated this method allows the dismembering of myxospores, isolation of intact and clean nematocysts and shell valves within 2h by low-cost. This new tool will facilitate subsequent analyses and enable a better understanding of the ecological and evolutionary significance of parasitic spores.

A fast and effective method for dissecting parasitic spores: myxozoans as an example.

Disassembling parasitic spores and acquiring the main subunits for analysis is a prerequisite for a deep understanding of the basic biology of parasites. Herein, we present a fast and efficient method to dissect myxospores in a few steps, which mainly involves sonication, and sucrose and Percoll density gradient ultracentrifugation. We tested our method on three myxozoan species and demonstrate that this method allows the dismembering of myxospores, and the isolation of intact and clean nematocysts and shell valves within 2 h at low cost. This new tool will facilitate subsequent analyses and enable a better understanding of the ecological and evolutionary significance of parasitic spores.

Molecular and light microscopy evidence for the transfer of Myxobolus honghuensis from Carassius auratus gibelio broodfish to progeny.

Myxozoans usually have a complex life cycle involving indirect transmission between vertebrate and invertebrate hosts. The vertical transmission of these parasites in vertebrate hosts has not been documented so far. Here, we assessed whether the myxozoan parasite Myxobolus honghuensis is vertically transmitted in naturally infected allogynogenetic gibel carp Carassius auratus gibelio (Bloch). M. honghuensis infection of broodfish, fertilized eggs and laboratory-cultured progeny was monitored in 2018 and 2019. The presporogonic stage was microscopically observed in the pharynx of broodfish and their progeny. In situ hybridization confirmed the presence of M. honghuensis presporogonic stage in the pharynx of broodfish and progeny. Nested PCR results showed that M. honghuensis was present in tissues and eggs of broodfish, fertilized eggs and their corresponding progeny. The sequences obtained from broodfish and progeny showed 98.0-99.8% similarity with ITS-5.8S rDNA of M. honghuensis. This study provides molecular and light microscopy evidence for the transfer of M. honghuensis from broodfish to progeny via the eggs, but it is insufficient to assert that M. honghuensis can transmit vertically in naturally infected allogynogenetic gibel carp. This is the first record about vertical transfer of myxozoan in the vertebrate host.

Anti-Parity-Time Symmetric Optical Four-Wave Mixing in Cold Atoms.

Non-Hermitian optical systems with parity-time (PT) symmetry have recently revealed many intriguing prospects that outperform conservative structures. The previous works are mostly rooted in complex arrangements with controlled gain-loss interplay. Here, we demonstrate anti-PT symmetry inherent in the nonlinear optical interaction based upon forward optical four-wave mixing in a laser-cooled atomic ensemble with negligible linear gain and loss. We observe that the pair of frequency modes undergo a nontrivial anti-PT phase transition between coherent power oscillation and optical parametric amplification in presence of a large phase mismatch.

Development of a multiplex PCR method for the simultaneous detection of four myxosporeans infecting gibel carp Carassius auratus gibelio.

Gibel carp Carassius auratus gibelio (Bloch), a commercially important freshwater-cultured fish in China, is threatened by myxosporeans, particularly Thelohanellus wuhanensis, Myxobolus honghuensis, M. wulii and M. turpisrotundus. Here, we developed a multiplex PCR assay for simultaneous detection of these 4 myxosporeans. The specific primers for each species were designed based on the 28S rDNA gene of T. wuhanensis, the ITS-5.8S rDNA of M. honghuensis and M. wulii, and the 18S rDNA gene of M. turpisrotundus. Specificity testing confirmed that the 4 primer sets have no cross-reactivity with other related myxosporean species tested. Detection limits of the multiplex PCR assay were 0.2, 0.3, 3.1 and 3.8 spores for T. wuhanensis, M. honghuensis, M. wulii and M. turpisrotundus, respectively. Following screening of 104 field samples, the analytical sensitivity of the present multiplex PCR assay was found to be similar to the sensitivity obtained by the singleplex PCR assays and was higher than that of microscopic examination. Moreover, Kappa analysis showed a strong agreement between the results of the singleplex and multiplex PCR assays, indicating that the developed multiplex PCR assay was an efficient approach for the diagnosis of the 4 myxosporeans infecting gibel carp.

Myxobolus pseudowulii sp. n. (Myxozoa: Myxosporea), a new skin parasite of yellow catfish Tachysurus fulvidraco (Richardson) and redescription of Myxobolus voremkhai (Akhmerov, 1960).

Two species of Myxobolus Bütschli, 1882 were found in yellow catfish Tachysurus fulvidraco (Richardson). A species of Myxobolus infecting the gills was morphologically identified as Myxobolus voremkhai (Akhmerov, 1960) and it was characterised here with additional morphological and molecular data. The other species of Myxobolus infecting the host's skin did not conform to any known myxosporean species. It is characterised by the presence of round, black or milky white plasmodia with black spots. Myxospores are pyriform in frontal view and lemon-shaped in lateral view, measuring 12.9-16.2 µm (14.6 ± 0.7 µm) in length, 8.1-10.8 µm (9.4 ± 0.5 µm) in width, and 6.1-8.1 µm (7.0 ± 0.4 µm) in thickness. Two ampullaceous polar capsules are slightly unequal in size, larger polar capsule 7.2-9.5 µm (7.9 ± 0.4 µm) long by 3.0-3.9 µm (3.5 ± 0.2 µm) wide, smaller capsule 6.9-8.0 µm (7.4 ± 0.3 µm) long by 2.9-3.9 µm (3.4 ± 0.2 µm) wide. Polar filaments are coiled with seven to nine turns. Histologically, the plasmodia develop in the stratum spongiosum of skin dermis, resulting in epithelial cell shedding and immunological cell infiltration. Given the morphological and molecular differences between this species and other species of Myxobolus, we proposed the name of Myxobolus pseudowulii sp. n. for this parasite from the skin of yellow catfish. Interestingly, some spores of the new species possess Henneguya-like caudal appendages. Phylogenetically, M. pseudowulii sp. n. and M. voremkhai infecting yellow catfish group together in one clade with other parasites of Siluriformes, indicating that parasites clustering according to the fish host order may be an important factor affecting the evolution of species within the Myxobolus clade.

Development of monoclonal antibodies against polar filaments and spore valves of Myxobolus honghuensis (Myxosporea: Bivalvulida).

Myxobolus honghuensis infects the pharynx of allogynogenetic gibel carp Carassius auratus gibelio (Bloch) and can cause high mortality. Only morphology-based diagnostic methods are currently available for clinical samples, but these methods are laborious and have low efficiency of detection. To overcome this problem, we designed a more sensitive diagnostic method. Two monoclonal antibodies (MAbs 1C7 and 3B7) were prepared by immunizing mice with soluble protein from sonicated M. honghuensis spores. Immunofluorescence analysis revealed that MAb 1C7 specifically reacts with polar filaments from spores, whereas MAb 3B7 identified protein localized on the spore valves. The isotypes of MAb 1C7 and MAb 3B7 were IgM and IgG1, respectively. Results of Western blot analysis revealed that MAb 1C7 recognized 2 prominent protein bands with molecular weights of 130 and 180 kDa, while MAb 3B7 recognized a protein band of 28 kDa. Thus, in this study we have developed 2 MAbs that have the potential for efficient detection of M. honghuensis. Moreover, identification of MAb 1C7 and MAb 3B7 allows for further studies of the functions and biochemical composition of polar filament and spore surface antigens.

The life cycle of Thelohanellus kitauei (Myxozoa: Myxosporea) infecting common carp (Cyprinus carpio) involves aurantiactinomyxon in Branchiura sowerbyi.

Thelohanellus kitauei is a freshwater myxosporean parasite causing intestinal giant cystic disease of common carp. To clarify the life cycle of T. kitauei, we investigated the oligochaete populations in China and Hungary. This study confirms two distinct aurantiactinomyxon morphotypes (Aurantiactinomyxon type 1 and Aurantiactinomyxon type 2) from Branchiura sowerbyi as developmental stages of the life cycle of T. kitauei. The morphological characteristics and DNA sequences of these two types are described here. Based on 18S rDNA sequence analysis, Aurantiactinomyxon type 1 (2048 bp) and Aurantiactinomyxon type 2 (2031 bp) share 99.2-99.4 %, 99.8-100 % similarity to the published sequences of T. kitauei, respectively. The 18S rDNA sequences of these two aurantiactinomyxon morphotypes share 99.4 % similarity, suggesting intraspecific variation within the taxon, possibly due to geographic origin. Phylogenetic analyses demonstrate the two aurantiactinomyxon types clustered with T. kitauei. Regardless, based on 18S rDNA synonymy, it is likely that Aurantiactinomyxon type 1 and 2 are conspecific with T. kitauei. This is the fourth elucidated two-host life cycle of Thelohanellus species and the first record of T. kitauei in Europe.

Histopathological and ultrastructural studies of Myxobolus turpisrotundus from allogynogenetic gibel carp Carassius auratus gibelio in China.

During an ongoing systematic survey on species diversity of myxozoans parasitising allogynogenetic gibel carp Carassius auratus gibelio (Bloch) in China, plasmodia were detected in the fins, lip, jaw, gill chamber, gill arches, operculum and oral cavity of infected fish. Combining the morphological and molecular data, the present species was identified as Myxobolus turpisrotundus Zhang, Wang, Li et Gong, 2010. Histopathological examination revealed that despite infecting different organs, M. turpisrotundus always occurred in dermis, demonstrating its affinity to this tissue. Histopathological effect of M. turpisrotundus on the host is relatively mild except parasites in the gill arches producing compression of the adipose tissue and heavy adductor muscles deformation with lymphohistiocytic infiltrates. In addition, the plasmodia in different sites were with the same complex structure arrangement: cup-like cells with unknown derivation, a thin collagenous fibril layer, areolar connective tissue, basement membrane and host epithelial cell. Ultrastructural analysis showed that the parasite has monosporic pansporoblast and sporogenesis followed the usual pattern of most of the myxosporeans.

Intraspecific morphometric variation in myxosporeans.

Morphometric data from spores of ten myxosporean species were statistically analysed to explore myxosporean intraspecific variation in measurements when obtained from a sample from: (1) the same plasmodium, (2) different plasmodia from the same host and (3) different host individuals and localities. In some cases, significant differences in spore dimensions were found between samples from the same plasmodium, highlighting the difficulty of obtaining representative measurements of myxosporean spore. In addition, significant differences in spore dimensions were found when plasmodia from the same site of infection were compared, suggesting that measurements of spores should come from several different plasmodia of the sampling to increase the reliability of the morphology data. Moreover, significant differences in spore dimensions were observed for most spore dimensions when data were compared between localities. In all cases, there was clear overlap in ranges of dimensions even when means differed significantly. The present statistical analysis shows that intraspecific morphometric variation of myxosporean species commonly occurs, highlighting the importance of reporting ranges of measurements for a species, not just the mean dimensions, and taking into account all evidence when assigning or describing myxosporean species.

Both Myosin-10 isoforms are required for radial neuronal migration in the developing cerebral cortex.

During embryonic development of the mammalian cerebral cortex, postmitotic cortical neurons migrate radially from the ventricular zone to the cortical plate. Proper migration involves the correct orientation of migrating neurons and the transition from a multipolar to a mature bipolar morphology. Herein, we report that the 2 isoforms of Myosin-10 (Myo10) play distinct roles in the regulation of radial migration in the mouse cortex. We show that the full-length Myo10 (fMyo10) isoform is located in deeper layers of the cortex and is involved in establishing proper migration orientation. We also demonstrate that fMyo10-dependent orientation of radial migration is mediated at least in part by the netrin-1 receptor deleted in colorectal cancer. Moreover, we show that the headless Myo10 (hMyo10) isoform is required for the transition from multipolar to bipolar morphologies in the intermediate zone. Our study reveals divergent functions for the 2 Myo10 isoforms in controlling both the direction of migration and neuronal morphogenesis during radial cortical neuronal migration.

First record of Chilodonella piscicola (Ciliophora: Chilodonellidae) from two endangered fishes, Schizothorax o'connori and Oxygymnocypris stewartii in Tibet.

Schizothorax o'connori and Oxygymnocypris stewartii are two endangered endemic Tibetan fishes that thrive in the Lhasa River at an average altitude over 4000 m. During artificial reproduction of endemic Tibetan fishes, the juvenile fish of S. o'connori and O. stewartii experienced mass mortality event. The causative agent is diagnosed to be a ciliate parasite, Chilodonella piscicola (syn. C. cyprini), which is common in various fishes. Here, we supplemented its description based on the morphological and molecular data. The body of C. piscicola is oval, 30-60 × 25-40 µm in vivo. Cyrtos is hook-like, composed of 9-10 toothed nematodesmal rods. Somatic kineties usually contain seven right kineties and nine left kineties. Two parallel circumoral kineties revolve round the cyrtos, and one preoral kinety extends to the anterior end of the fourth left-most kinety. Terminal fragment kinety is linear and on the top left of dorsal side. Sequence alignments revealed that the present SSU rDNA and ITS1-5.8S-ITS2 sequences are both most similar to the sequences of C. uncinata with the similarities of 98.2 and 99.5%. The phylogenetic analyses showed that C. piscicola is sister to other Chilodonella species, whereas C. cyprini (FJ873805) cluster with Tetrahymena species. Molecular analysis shows that the ITS1-5.8S-ITS2 sequence of C. cyprini in GenBank is unreliable. Our study extended the host range of C. piscicola and supplemented and revised the molecular data. Besides, as far as we know, this is the first record of C. piscicola in Tibetan plateau.

Up-regulation of nuclear factor E2-related factor 2 upon SVCV infection.

Nuclear factor E2 - related factor 2 (Nrf2) is a crucial transcription factor that regulates the basal and inducible expression of many antioxidant response element (ARE)-dependent genes, including heme oxygenase-1 (HO-1) and superoxide dismutase 1 (SOD1). The Nrf2/ARE pathway has been regarded as a critical switch in the initiation of cellular defence systems for surviving oxidative insults and viral infection. In this study, the Nrf2 gene of EPC cells, which is originally derived from Pimephales promelas, was cloned, and an investigation on the interactions between Nrf2 and spring viraemia of carp virus (SVCV) was performed. These results demonstrated that the virus facilitated the nuclear accumulation of Nrf2 and up-regulated its transcriptional and protein profiles in EPC cells. In addition, exogenous activation of Nrf2 conferred EPC cells with a higher cellular total antioxidant capacity via an increase in the expression of HO-1 and SOD1, but did not suppress the replication of SVCV.

Proliferation and resistance difference of a liver-parasitized myxosporean in two different gynogenetic clones of gibel carp.

Some myxosporeans have been demonstrated to be harmful to worldwide aquaculture. However, the proliferation information has remained unclear in the fish hosts. In this study, we utilized the mix-culturing equality to reveal significant difference in disease assistance between two different clones of gibel carp, in which clone D had been cultured for nearly 40 years, whereas clone A(+) was a newly created clone. According to morphological and genetic analysis of isolated spores, the diseasing pathogen was identified as Myxobolus wulii of the genus Myxobolus in Myxosporea. Subsequently, a polyclonal antibody specific to soluble proteins of the purified spores was generated. Using the antibody, we performed immunofluorescence observation of the liver lump sections sampled from the heavily diseased clone D individuals, and found that the liver lumps were completely composed of numerous honeycomb-like cysts, full of maturing and mature myxosporean spores, and almost all of liver tissues were destroyed. Comparative co-localization detection revealed a significantly inducing expression of apo-14 protein around the infected myxosporean sporoplasms and plasmodia, and the inducing level was much stronger in clone A(+) than in clone D. Furthermore, a primarily screening of 15 different major histocompatibility complex class Iα variants also excavated major variants that respectively belong to clones D and A(+). Therefore, these data provide significant information for differences in myxosporean proliferation and disease resistance in fish clone hosts with different genetic background. Further studies on myxosporean development and the mechanism for disease resistance will be very important for preventing and controlling the parasitic myxosporean disease.

Photon-number-resolved detection of photon-subtracted thermal light.

We examine the photon statistics of photon-subtracted thermal light using photon-number-resolved detection. We demonstrate experimentally that the photon number distribution transforms from a Bose-Einstein distribution to a Poisson distribution as the number of subtracted photons increases. We also show that second- and higher-order photon correlation functions can be directly determined from the photon-number-resolved detection measurements of a single optical beam.

Identification and characterization of one novel type of Triactinospomyxon with short spore axis.

This study identifies and characterizes one novel type of triactinospomyxon in oligochaete specimen of Branchiura sowerbyi Beddard collected from a fish pond used for rearing gibel carp located in Caidian Experimental Station of the Institute of Hydrobiology. It is nominated as Triactinospomyxon caidianensis type. The spore is of characteristic triactinomyxon "anchor" shape and possesses a spore body with sporoplasm containing 32 germ cells, 3 polar capsules, and 3 caudal processes. Compared with other triactinomyxon spores described previously, T. caidianensis type has a short spore axis with 76.5 µm in length and a very short style with 38.9 µm in length. Molecular analyses on 18S rDNA sequences indicate that the novel T. caidianensis type is most closely related to Triactinomyxon sp SA-2005, Antonactinomyxon sp KAB-2001, and Synactinomyxon sp KAB-2001 with 80.33% to 81.92% identities. On the basis of spore morphology and genetic data, the T. caidianensis type presented in this paper differs from those already known and described in the literatures.

Quantitative Insights into the Contribution of Nematocysts to the Adaptive Success of Cnidarians Based on Proteomic Analysis.

Nematocysts are secretory organelles in cnidarians that play important roles in predation, defense, locomotion, and host invasion. However, the extent to which nematocysts contribute to adaptation and the mechanisms underlying nematocyst evolution are unclear. Here, we investigated the role of the nematocyst in cnidarian evolution based on eight nematocyst proteomes and 110 cnidarian transcriptomes/genomes. We detected extensive species-specific adaptive mutations in nematocyst proteins (NEMs) and evidence for decentralized evolution, in which most evolutionary events involved non-core NEMs, reflecting the rapid diversification of NEMs in cnidarians. Moreover, there was a 33-55 million year macroevolutionary lag between nematocyst evolution and the main phases of cnidarian diversification, suggesting that the nematocyst can act as a driving force in evolution. Quantitative analysis revealed an excess of adaptive changes in NEMs and enrichment for positively selected conserved NEMs. Together, these findings suggest that nematocysts may be key to the adaptive success of cnidarians and provide a reference for quantitative analyses of the roles of phenotypic novelties in adaptation.