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Current Biology : CB Apr 2017Platyhelminthes (flatworms) have captivated the imagination of biologists for centuries. Indeed, planarian flatworms were used as experimental models decades before...
Platyhelminthes (flatworms) have captivated the imagination of biologists for centuries. Indeed, planarian flatworms were used as experimental models decades before Caenorhabditis elegans became known as 'the worm'. Although planarians experienced a brief fall from grace, with the advent of molecular tools, planarians, such as Schmidtea mediterranea, have emerged in recent years as powerful models to study the basis of stem cell regulation and tissue regeneration. Flatworms are not just everyone's favorite experimental subjects from high school biology - they also include some of nature's most successful parasites, many of which have plagued humans throughout our history. This Primer will focus on several aspects of the remarkable biology found throughout the phylum Platyhelminthes.
Topics: Animals; Host-Parasite Interactions; Platyhelminths; Regeneration; Reproduction; Stem Cells
PubMed: 28376328
DOI: 10.1016/j.cub.2017.02.016 -
Advances in Experimental Medicine and... 2018Lophotrochozoa is a sister taxon of Ecdysozoa in the Protostomia that includes mollusks, annelids, brachiopods, and platyhelminths. Recent studies have clarified the... (Review)
Review
Lophotrochozoa is a sister taxon of Ecdysozoa in the Protostomia that includes mollusks, annelids, brachiopods, and platyhelminths. Recent studies have clarified the structure, expression, and roles of lophotrochozoan Zic family genes. Zic genes in oligochaete annelid Tubifex tubifex (freshwater sludge worm) and polychaete annelid Capitella teleta (bristle worm) are commonly expressed in a subset of developing brain and mesoderm derivatives. The latter includes the naïve mesoderm and the associated chaetal sacs in each body segment, although the segmentation processes differ between the two species. Furthermore, in brachiopod Terebratalia transversa (lamp shell), Zic is expressed in the anterior ectodermal domains and mesodermal derivatives, including those associated with the chaetal sacs. This result suggests the common involvement of Zic genes in the development of chaetae, a lophotrochozoan novelty acquired in the course of evolution. In addition, the highly simplified lophotrochozoan Dicyema acuticephalum (dicyemid mesozoan, a cephalopod endoparasite), which lost its gut, nervous system, and muscles during evolution, expresses its Zic genes in hermaphroditic gonads, highlighting the role of Zic genes in germ cell development. The role of Zic in head regeneration was revealed in studies on platyhelminth Schmidtea mediterranea (freshwater planarian). Planarian Zic expression was induced in a subpopulation of neoblasts that includes adult pluripotent stem cells. It is needed for head regeneration and production of an anterior signaling center. Suppression of Wnt-β-catenin signaling underlies Zic-mediated head regeneration, reminiscent of Wnt-β-catenin suppression by vertebrate Zic genes. Taken together, studies on the lophotrochozoan Zic genes are essential to understanding not only the roles of these genes in body plan evolution but also the molecular mechanism underlying adult stem cell regulation.
Topics: Animals; Helminth Proteins; Oligochaeta; Planarians; Polychaeta; Transcription Factors; Zinc Fingers
PubMed: 29442318
DOI: 10.1007/978-981-10-7311-3_5 -
Parasitology Research Apr 2022The first cestode genomes were obtained by an international consortium led by the Wellcome Sanger Institute that included representative institutions from countries... (Review)
Review
The first cestode genomes were obtained by an international consortium led by the Wellcome Sanger Institute that included representative institutions from countries where the sequenced parasites have been studied for decades, in part because they are etiological agents of endemic diseases (Argentina, Uruguay, Mexico, Canada, UK, Germany, Switzerland, Ireland, USA, Japan, and China). After this, several complete genomes were obtained reaching 16 species to date. Cestode genomes have smaller relative size compared to other animals including free-living flatworms. Moreover, the features genome size and repeat content seem to differ in the two analyzed orders. Cyclophyllidean species have smaller genomes and with fewer repetitive content than Diphyllobothriidean species. On average, cestode genomes have 13,753 genes with 6 exons per gene and 41% GC content. More than 5,000 shared cestode proteins were accurately annotated by the integration of gene predictions and transcriptome evidence being more than 40% of these proteins of unknown function. Several gene losses and reduction of gene families were found and could be related to the extreme parasitic lifestyle of these species. The application of cutting-edge sequencing technology allowed the characterization of the terminal sequences of chromosomes that possess unique characteristics. Here, we review the current status of knowledge of complete cestode genomes and place it within a comparative genomics perspective. Multidisciplinary work together with the implementation of new technologies will provide valuable information that can certainly improve our chances to finally eradicate or at least control diseases caused by cestodes.
Topics: Animals; Cestoda; Cestode Infections; Genomics; Platyhelminths; Sequence Analysis, DNA
PubMed: 34665308
DOI: 10.1007/s00436-021-07346-x -
BioMed Research International 2015Flatworms are one of the most diverse groups within Lophotrochozoa with more than 20,000 known species, distributed worldwide in different ecosystems, from the... (Review)
Review
Flatworms are one of the most diverse groups within Lophotrochozoa with more than 20,000 known species, distributed worldwide in different ecosystems, from the free-living organisms in the seas and lakes to highly specialized parasites living in a variety of hosts, including humans. Several infections caused by flatworms are considered major neglected diseases affecting countries in the Americas, Asia, and Africa. For several decades, a particular interest on free-living flatworms was due to their ability to regenerate considerable portions of the body, implying the presence of germ cells that could be important for medicine. The relevance of reverse genetics for this group is clear; understanding the phenotypic characteristics of specific genes will shed light on developmental traits of free-living and parasite worms. The genetic manipulation of flatworms will allow learning more about the mechanisms for tissue regeneration, designing new and more effective anthelmintic drugs, and explaining the host-parasite molecular crosstalk so far partially inaccessible for experimentation. In this review, availability of transfection techniques is analyzed across flatworms, from the initial transient achievements to the stable manipulations now developed for free-living and parasite species.
Topics: Animals; Helminths; Humans; Platyhelminths; Regenerative Medicine; Transfection
PubMed: 26090388
DOI: 10.1155/2015/206161 -
Marine Drugs Jan 2021Marine invertebrates are promising sources of novel bioactive secondary metabolites, and organisms like sponges, ascidians and nudibranchs are characterised by... (Review)
Review
Marine invertebrates are promising sources of novel bioactive secondary metabolites, and organisms like sponges, ascidians and nudibranchs are characterised by possessing potent defensive chemicals. Animals that possess chemical defences often advertise this fact with aposematic colouration that potential predators learn to avoid. One seemingly defenceless group that can present bright colouration patterns are flatworms of the order Polycladida. Although members of this group have typically been overlooked due to their solitary and benthic nature, recent studies have isolated the neurotoxin tetrodotoxin from these mesopredators. This review considers the potential of polyclads as potential sources of natural products and reviews what is known of the activity of the molecules found in these animals. Considering the ecology and diversity of polyclads, only a small number of species from both suborders of Polycladida, Acotylea and Cotylea have been investigated for natural products. As such, confirming assumptions as to which species are in any sense toxic or if the compounds they use are biosynthesised, accumulated from food or the product of symbiotic bacteria is difficult. However, further research into the group is suggested as these animals often display aposematic colouration and are known to prey on invertebrates rich in bioactive secondary metabolites.
Topics: Animals; Biological Products; Platyhelminths; Protein Structure, Secondary; Protein Structure, Tertiary; Secondary Metabolism
PubMed: 33494164
DOI: 10.3390/md19020047 -
Molecular and Biochemical Parasitology Oct 2019Nuclear receptors (NRs) belong to a large protein superfamily which includes intracellular receptors for secreted hydrophobic signal molecules, such as steroid hormones... (Review)
Review
Nuclear receptors (NRs) belong to a large protein superfamily which includes intracellular receptors for secreted hydrophobic signal molecules, such as steroid hormones and thyroid hormones. They regulate development and reproduction in metazoans by binding to the promoter region of their target gene to activate or repress mRNA synthesis. Isolation and characterization of NRs in the parasitic trematode Schistosoma mansoni identified two homologues of mammalian thyroid receptor (TR). This was the first known protostome exhibiting TR homologues. Three novel NRs each possess a novel set of two DNA binding domains (DBD) in tandem with a ligand binding domain (LBD) (2DBD-NRs) isolated in Schistosoma mansoni revealed a novel NR modular structure: A/B-DBD-DBD-hinge-LBD. Full length cDNA of several NRs have been isolated and studied in the parasitic trematodes S. mansoni, S. japonicum and in the cestode Echinococcus multilocularis. The genome of the blood flukes S. mansoni, S. japonicum and S. haematobium, the liver fluke Clonorchis sinensis and the cestode Echinococcus multilocularis have been sequenced. Study of the NR complement in parasitic Platyhelminths will help us to understand the role of NRs in regulation of their development and understand the evolution of NR in animals.
Topics: Animals; Clonorchis sinensis; Echinococcus multilocularis; Evolution, Molecular; Helminth Proteins; Phylogeny; Platyhelminths; Receptors, Cytoplasmic and Nuclear; Schistosoma; Schistosoma mansoni
PubMed: 31470045
DOI: 10.1016/j.molbiopara.2019.111218 -
Frontiers in Cellular and Infection... 2021An organism responds to the invading pathogens such as bacteria, viruses, protozoans, and fungi by engaging innate and adaptive immune system, which functions by... (Review)
Review
An organism responds to the invading pathogens such as bacteria, viruses, protozoans, and fungi by engaging innate and adaptive immune system, which functions by activating various signal transduction pathways. As invertebrate organisms (such as sponges, worms, cnidarians, molluscs, crustaceans, insects, and echinoderms) are devoid of an adaptive immune system, and their defense mechanisms solely rely on innate immune system components. Investigating the immune response in such organisms helps to elucidate the immune mechanisms that vertebrates have inherited or evolved from invertebrates. Planarians are non-parasitic invertebrates from the phylum Platyhelminthes and are being investigated for several decades for understanding the whole-body regeneration process. However, recent findings have emerged planarians as a useful model for studying innate immunity as they are resistant to a broad spectrum of bacteria. This review intends to highlight the research findings on various antimicrobial resistance genes, signaling pathways involved in innate immune recognition, immune-related memory and immune cells in planarian flatworms.
Topics: Animals; Immune System; Immunity, Innate; Insecta; Planarians; Signal Transduction
PubMed: 33732660
DOI: 10.3389/fcimb.2021.619081 -
Parasitology Feb 2015The genomes of more than 20 helminths have now been sequenced. Here we perform a meta-analysis of all sequenced genomes of nematodes and Platyhelminthes, and attempt to... (Meta-Analysis)
Meta-Analysis Review
The genomes of more than 20 helminths have now been sequenced. Here we perform a meta-analysis of all sequenced genomes of nematodes and Platyhelminthes, and attempt to address the question of what are the defining characteristics of helminth genomes. We find that parasitic worms lack systems for surface antigenic variation, instead maintaining infections using their surfaces as the first line of defence against the host immune system, with several expanded gene families of genes associated with the surface and tegument. Parasite excretory/secretory products evolve rapidly, and proteases even more so, with each parasite exhibiting unique modifications of its protease repertoire. Endoparasitic flatworms show striking losses of metabolic capabilities, not matched by nematodes. All helminths do however exhibit an overall reduction in auxiliary metabolism (biogenesis of co-factors and vitamins). Overall, the prevailing pattern is that there are few commonalities between the genomes of independently evolved parasitic worms, with each parasite having undergone specific adaptations for their particular niche.
Topics: Adaptation, Physiological; Animals; Biological Evolution; Genome, Helminth; Helminths; Immune System; Nematoda; Parasites; Platyhelminths; Transcriptome
PubMed: 25482650
DOI: 10.1017/S0031182014001449 -
Current Biology : CB Sep 2022A recent paper suggests that the flatworm Schmidtea mediterranea has an autosome that is 'primed' to evolve into a sex chromosome. However, this chromosome could be a...
A recent paper suggests that the flatworm Schmidtea mediterranea has an autosome that is 'primed' to evolve into a sex chromosome. However, this chromosome could be a balanced-lethal system and may illuminate these puzzling systems.
Topics: Animals; Platyhelminths; Sex Chromosomes
PubMed: 36099896
DOI: 10.1016/j.cub.2022.07.043 -
Advances in Experimental Medicine and... 2019The platyhelminth class Trematoda comprises two subclasses with largely disparate species diversity, the small Aspidogastrea with c.80 species and the speciose Digenea...
The platyhelminth class Trematoda comprises two subclasses with largely disparate species diversity, the small Aspidogastrea with c.80 species and the speciose Digenea with c.18,000 species, which has attracted much effort towards our understanding of evolutionary relationships among suprageneric taxa. This chapter focuses on insights into the classification of the Digenea that have become apparent from our advanced understanding of both morphological and molecular data. The field of molecular systematics of the Digenea has experienced significant advances over the past 15 years. Phylogenetic analyses of sequence data predominantly from the 18S and 28S rRNA genes have incorporated a considerable diversity of taxa thus increasing the accuracy of phylogenetic inferences at higher taxonomic levels. As a result, the status of long-standing supraspecific taxa has been revised, new higher-level taxa have been defined, and inferences made in association with morphological and life-cycle evidence. A substantial effort has been made towards a classification reflecting the natural system of the Digenea by considering morphological evidence in conjunction with phylogenies inferred from molecular data; this has resulted in considerable congruence. However, limited taxon sampling in the phylogeny of the Digenea still remains relevant especially in relation to some higher-level taxa, and an outline of these omissions is presented. A framework that has led to robust estimates of phylogeny is outlined, and the application of advanced morphological and molecular approaches in digenean taxonomy and systematics is illustrated using the most comprehensively studied digenean superfamilies.
Topics: Animals; Biodiversity; Phylogeny; Trematoda
PubMed: 31297758
DOI: 10.1007/978-3-030-18616-6_2