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Development Genes and Evolution Mar 2013Planarians are members of the Platyhelminthes (flatworms). These animals have evolved a remarkable stem cell system. A single pluripotent adult stem cell type... (Review)
Review
Planarians are members of the Platyhelminthes (flatworms). These animals have evolved a remarkable stem cell system. A single pluripotent adult stem cell type ("neoblast") gives rise to the entire range of cell types and organs in the planarian body plan, including a brain, digestive-, excretory-, sensory- and reproductive systems. Neoblasts are abundantly present throughout the mesenchyme and divide continuously. The resulting stream of progenitors and turnover of differentiated cells drive the rapid self-renewal of the entire animal within a matter of weeks. Planarians grow and literally de-grow ("shrink") by the food supply-dependent adjustment of organismal turnover rates, scaling body plan proportions over as much as a 50-fold size range. Their dynamic body architecture further allows astonishing regenerative abilities, including the regeneration of complete and perfectly proportioned animals even from tiny tissue remnants. Planarians as an experimental system, therefore, provide unique opportunities for addressing a spectrum of current problems in stem cell research, including the evolutionary conservation of pluripotency, the dynamic organization of differentiation lineages and the mechanisms underlying organismal stem cell homeostasis. The first part of this review focuses on the molecular biology of neoblasts as pluripotent stem cells. The second part examines the fascinating mechanistic and conceptual challenges posed by a stem cell system that epitomizes a universal design principle of biological systems: the dynamic steady state.
Topics: Animals; Homeostasis; Planarians; Pluripotent Stem Cells; Regeneration; Stem Cells
PubMed: 23138344
DOI: 10.1007/s00427-012-0426-4 -
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 -
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 -
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 -
Nucleic Acids Research Mar 2022Parasitic helminths infecting humans are highly prevalent infecting ∼2 billion people worldwide, causing inflammatory responses, malnutrition and anemia that are the...
Parasitic helminths infecting humans are highly prevalent infecting ∼2 billion people worldwide, causing inflammatory responses, malnutrition and anemia that are the primary cause of morbidity. In addition, helminth infections of cattle have a significant economic impact on livestock production, milk yield and fertility. The etiological agents of helminth infections are mainly Nematodes (roundworms) and Platyhelminths (flatworms). G-quadruplexes (G4) are unusual nucleic acid structures formed by G-rich sequences that can be recognized by specific G4 ligands. Here we used the G4Hunter Web Tool to identify and compare potential G4 sequences (PQS) in the nuclear and mitochondrial genomes of various helminths to identify G4 ligand targets. PQS are nonrandomly distributed in these genomes and often located in the proximity of genes. Unexpectedly, a Nematode, Ascaris lumbricoides, was found to be highly enriched in stable PQS. This species can tolerate high-stability G4 structures, which are not counter selected at all, in stark contrast to most other species. We experimentally confirmed G4 formation for sequences found in four different parasitic helminths. Small molecules able to selectively recognize G4 were found to bind to Schistosoma mansoni G4 motifs. Two of these ligands demonstrated potent activity both against larval and adult stages of this parasite.
Topics: Animals; Cattle; G-Quadruplexes; Genome; Helminths; Humans; Ligands; Nematoda; Parasites; Platyhelminths
PubMed: 35234933
DOI: 10.1093/nar/gkac129 -
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 -
Current Protocols in Immunology May 2001The trematode parasites in the family Schistosomatidae (phylum Platyhelminthes) infect a wide range of vertebrates. Three species of the genus Schistosoma are of major...
The trematode parasites in the family Schistosomatidae (phylum Platyhelminthes) infect a wide range of vertebrates. Three species of the genus Schistosoma are of major medical importance. This unit deals exclusively with the parasite Schistosoma mansoni, which is the species most frequently maintained in the laboratory. Among the far-ranging investigations in the immunology of schistosomiasis are studies in vaccine development, immunopathology of granulomatous inflammation and fibrosis, eosinophil function, and in vivo regulation of T(H)1 and T(H)2 responses. This unit describes maintenance and collection procedures for various stages of the schistosome that have immunologic interest, including infection of mice with cercariae, collection of cercariae, preparation of in vitro-derived schistosomules and in vivo-derived schistosomules, and collection of adult worms and eggs. Included also are techniques for preparing soluble egg antigen (SEA), one of the more commonly used schistosome antigenic preparations. A discussion is given of the basic steps that are important in maintaining the snail intermediate host, and infecting the snails with schistosome miracidia. The unit deals exclusively with the parasite Schistosoma mansoni, which is the species most frequently maintained in the laboratory. Since part of the life cycle of all schistosomes involves a snail host, a description of proper maintenance for the snails is provided. Often, problems in experiments can be traced back to improper snail and parasite maintenance, or lack of attention to detail during mammalian exposure to the infective stage (cercaria) of the parasite.
Topics: Animals; Antigens, Helminth; Humans; Life Cycle Stages; Mice; Schistosoma mansoni; Schistosomiasis; Snails; Solubility
PubMed: 18432750
DOI: 10.1002/0471142735.im1901s28 -
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 -
Sleep May 2022Sleep is a prominent behavioral and biochemical state observed in all animals studied, including platyhelminth flatworms. Investigations into the biochemical mechanisms...
STUDY OBJECTIVES
Sleep is a prominent behavioral and biochemical state observed in all animals studied, including platyhelminth flatworms. Investigations into the biochemical mechanisms associated with sleep-and wakefulness-are important for understanding how these states are regulated and how that regulation changed with the evolution of new types of animals. Unfortunately, beyond a handful of vertebrates, such studies on invertebrates are rare.
METHODS
We investigated the effect of seven neurotransmitters, and one pharmacological compound, that modulate either sleep or wakefulness in mammals, on flatworms (Girardia tigrina). Flatworms were exposed via ingestion and diffusion to four neurotransmitters that promote wakefulness in vertebrates (acetylcholine, dopamine, glutamate, histamine), and three that induce sleep (adenosine, GABA, serotonin) along with the H1 histamine receptor antagonist pyrilamine. Compounds were administered over concentrations spanning three to five orders of magnitude. Flatworms were then transferred to fresh water and video recorded for analysis.
RESULTS
Dopamine and histamine decreased the time spent inactive and increased distance traveled, consistent with their wake-promoting effect in vertebrates and fruit flies; pyrilamine increased restfulness and GABA showed a nonsignificant trend towards promoting restfulness in a dose-dependent manner, in agreement with their sleep-inducing effect in vertebrates, fruit flies, and Hydra. Similar to Hydra, acetylcholine, glutamate, and serotonin, but also adenosine, had no apparent effect on flatworm behavior.
CONCLUSIONS
These data demonstrate the potential of neurotransmitters to regulate sleep and wakefulness in flatworms and highlight the conserved action of some neurotransmitters across species.
Topics: Acetylcholine; Adenosine; Animals; Dopamine; Glutamic Acid; Histamine; Mammals; Neurotransmitter Agents; Platyhelminths; Pyrilamine; Serotonin; Sleep; Wakefulness; gamma-Aminobutyric Acid
PubMed: 35554581
DOI: 10.1093/sleep/zsac053