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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 -
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 -
PloS One 2019Microstomidae (Platyhelminthes: Macrostomorpha) diversity has been almost entirely ignored within recent years, likely due to inconsistent and often old taxonomic... (Review)
Review
Microstomidae (Platyhelminthes: Macrostomorpha) diversity has been almost entirely ignored within recent years, likely due to inconsistent and often old taxonomic literature and a general rarity of sexually mature collected specimens. Herein, we reconstruct the phylogenetic relationships of the group using both previously published and new 18S and CO1 gene sequences. We present some taxonomic revisions of Microstomidae and further describe 8 new species of Microstomum based on both molecular and morphological evidence. Finally, we briefly review the morphological taxonomy of each species and provide a key to aid in future research and identification that is not dependent on reproductive morphology. Our goal is to clarify the taxonomy and facilitate future research into an otherwise very understudied group of tiny (but important) flatworms.
Topics: Animals; DNA, Helminth; Phylogeny; Platyhelminths; Reproduction
PubMed: 31017906
DOI: 10.1371/journal.pone.0212073 -
Advances in Parasitology 2001This review is the first to draw together knowledge about bioadhesives secreted by a group of parasites. Mechanisms of mechanical attachment are well known among... (Review)
Review
This review is the first to draw together knowledge about bioadhesives secreted by a group of parasites. Mechanisms of mechanical attachment are well known among parasites, but some can also attach to host surfaces by chemical means using a thin layer of adhesive material secreted at the parasite-host interface. Attachment by adhesives to living surfaces has not been studied in detail previously. A significant volume of research has determined much about the chemistry and nature of bioadhesives secreted by various marine macroinvertebrates from different phyla for attachment to inert substrates. Mussels and barnacles are sessile and adhere permanently, whereas starfish display temporary but firm adhesion during locomotion, feeding and burrowing. We focus on the Platyhelminthes that comprises the largely free-living Turbellaria and the wholly parasitic Monogenea, Cestoda, Digenea and Aspidogastrea. The term tissue adhesion is introduced to describe attachment by adhesives to epithelial surfaces such as fish epidermis and the lining of the vertebrate gut. These living layers regenerate rapidly, secrete mucus, are a site for immune activity and are therefore especially hostile environments for organisms that inhabit them, presenting a significant challenge for adhesion. Not all platyhelminths adhere to living surfaces and types of adhesion to inert substrates by the free-living turbellarians are also reviewed. Tissue adhesion is particularly well exemplified by monopisthocotylean monogeneans, parasites that are especially mobile as larvae, juveniles and adults on the epidermis of the body and gill surfaces of fish. These monogeneans secrete adhesives from the anterior end when they move from site to site, but some have secondarily developed adhesives at the posterior end to supplement or replace mechanical attachment by hooks and/or by suction. The temporary but tenacious anterior adhesives of monogeneans display remarkable properties of instant attachment to and detachment from their host fish surfaces. In contrast to the mobility of turbellarians and monopisthocotylean monogeneans and the simplicity of their direct life cycles, the largely endoparasitic Cestoda and Digenea are considered to be less mobile as adults. The complex cestode and digenean life cycles, involving intermediate hosts, place different demands on their various stages. Diverse, mostly anterior, gland cells in larvae, metacestodes and adults of the true tapeworms (Eucestoda), and in larval and adult Gyrocotylidea and Amphilinidea are reviewed. Conspicuous gland cells, mostly but not exclusively at the anterior end, in miracidia, cercariae and adults of digeneans and in cotylocidia and adults of aspidogastreans are also reviewed. Unlike turbellarians and monogeneans, accounts of unequivocal adhesive secretions in the Cestoda, but especially in the Digenea and Aspidogastrea, are relatively rare. The primary purpose of many conspicuous glands in the different stages of these mostly endoparasitic flatworms is for penetration into, or escape from, different hosts in their life cycle. We provide a detailed review of current knowledge about adhesion (in the sense of a thin layer of chemical material) in the Platyhelminthes including uses among eggs, larval, juvenile and adult stages. Information on structure, morphology and ultrastructure of the various adhesive systems that have been described is reviewed. Application of the 'duo gland' model is discussed. Comparisons are made between the little that is known about the chemistry of flatworm adhesives and the significant knowledge of the chemical nature of other invertebrate bioadhesives, especially those from marine macroinvertebrates. The potential importance of adhesives in parasitism is discussed. (ABSTRACT TRUNCATED)
Topics: Animals; Cell Adhesion; Cestode Infections; Platyhelminths; Symbiosis; Trematode Infections; Turbellaria
PubMed: 11013756
DOI: 10.1016/s0065-308x(01)48006-7 -
International Journal For Parasitology Jun 1997Some of the most significant alterations to the basic turbellarian plan are evident in the adaptations that relate to the acquisition of food by parasitic flatworms,... (Review)
Review
Some of the most significant alterations to the basic turbellarian plan are evident in the adaptations that relate to the acquisition of food by parasitic flatworms, reflecting the most potent of selection pressures in initiating and maintaining the host-parasite association. Nutritionally, ectoparasitic monogeneans show most correspondence with the predatory turbellarians, with certain monopisthocotylean members feeding by means of a protrusible pharynx and extracorporeal digestion, as skin-browsers of fish, with extensive intracellular digestion involving lysosomal enzymes in a well-differentiated gut. The more sheltered vascularised gill chamber of fish provides many polyopisthocotylean monogeneans with a totally renewable and more comprehensive diet in the form of blood, but haematophagy has necessitated a number of digestive adaptations, not least in resolving the problem of intracellular accumulations of haematin pigment. Haematophagy is the predominant feeding strategy of digeneans, but in contrast to monogeneans digestion of blood is largely extracellular; in schistosomes digestion is rapid, involving a battery of cathepsin-like cysteine proteinases and aminopeptidases. The external surfaces of all parasitic flatworms depart from turbellarian character and are composed of a multifunctional syncytial tegument, which is permeable to a variety of small organic solutes, some crossing by passive diffusion, others via facilitated or active mediated transport. The relative roles of the tegument and gut in trematode nutrition are difficult to assess, but can be related to the nature of the microhabitat within the host. Cestodes are highly adapted intestinal parasites bereft of any vestige of gut, and their tegument has become elaborated into a sophisticated and highly efficient digestive-absorptive layer, rivalling the vertebrate mucosa in its ability to gain kinetic advantage in the selective uptake of nutrient at the host-parasite interface. The patterns of energy metabolism in adult flatworm parasites are generally anaerobic and based on glycogen, with abbreviated metabolic pathways and the loss of biosynthetic capacities.
Topics: Animal Nutritional Physiological Phenomena; Animals; Cestoda; Digestion; Fasciola hepatica; Female; Host-Parasite Interactions; Male; Platyhelminths; Schistosoma; Trematoda
PubMed: 9229252
DOI: 10.1016/s0020-7519(97)00011-8 -
The International Journal of... 2012Within the free-living platyhelminths, the triclads, or planarians, are the best-known group, largely as a result of long-standing and intensive research on... (Review)
Review
Within the free-living platyhelminths, the triclads, or planarians, are the best-known group, largely as a result of long-standing and intensive research on regeneration, pattern formation and Hox gene expression. However, the group's evolutionary history has been long debated, with controversies ranging from their phyletic structure and position within the Metazoa to the relationships among species within the Tricladida. Over the the last decade, with the advent of molecular phylogenies, some of these issues have begun to be resolved. Here, we present an up-to-date summary of the main phylogenetic changes and novelties with some comments on their evolutionary implications. The phylum has been split into two groups, and the position of the main group (the Rhabdithophora and the Catenulida), close to the Annelida and the Mollusca within the Lophotrochozoa, is now clear. Their internal relationships, although not totally resolved, have been clarified. Tricladida systematics has also experienced a revolution since the implementation of molecular data. The terrestrial planarians have been demonstrated to have emerged from one of the freshwater families, giving a different view of their evolution and greatly altering their classification. The use of molecular data is also facilitating the identification of Tricladida species by DNA barcoding, allowing better knowledge of their distribution and genetic diversity. Finally, molecular phylogenetic and phylogeographical analyses, taking advantage of recent data, are beginning to give a clear picture of the recent history of the Dugesia and Schmidtea species in the Mediterranean.
Topics: Animals; Biological Evolution; Phylogeny; Platyhelminths
PubMed: 22450992
DOI: 10.1387/ijdb.113441mr -
International Journal For Parasitology Feb 1987
Review
Topics: Animals; Cestoda; Larva; Morphogenesis; Ovum; Platyhelminths; Turbellaria
PubMed: 3294636
DOI: 10.1016/0020-7519(87)90047-6 -
International Journal For Parasitology Apr 1995Polystome phylogeny is examined, with emphasis on the dimorphism of the frog parasite Polystoma integerrimum, which exists in a fully differentiated and a neotenic form,... (Review)
Review
Polystome phylogeny is examined, with emphasis on the dimorphism of the frog parasite Polystoma integerrimum, which exists in a fully differentiated and a neotenic form, and the evolutionary development of exclusively neotenic genera. Protopolystoma, which infects the aquatic toad Xenopus, has essentially the same morphology as the neotenic (branchial) adult of P. integerrimum and is interpreted as a neotenic genus; however, it inhabits the bladder of its host, the infection site of the normal adult of the dimorphic species. The sphyranurid Sphyranura, ectoparasitic on the external gills of the mud puppy Necturus, resembles the two-sucker larva of P. integerrimum in possessing a single pair of haptorial suckers in place of the 6 suckers of adult polystomes, and is probably a neotenic parasite associated with a neotenic host. The neotenic animals in general are parasites of aquatic hosts, and the uterus is lost or reduced in these genera; by contrast, uterine function is greatly enhanced among polystomes infecting amphibians best adapted to terrestrial life.
Topics: Animals; Phylogeny; Platyhelminths; Rana temporaria
PubMed: 7635619
DOI: 10.1016/0020-7519(94)00138-e -
Advances in Parasitology 2005The application of molecular systematics to the parasitic Platyhelminthes (Cestoda, Digenea and Monogenea) over the last decade has advanced our understanding of their... (Review)
Review
The application of molecular systematics to the parasitic Platyhelminthes (Cestoda, Digenea and Monogenea) over the last decade has advanced our understanding of their interrelationships and evolution substantially. Here we review the current state of play and the early works that led to the molecular-based hypotheses that now predominate in the field; advances in their systematics, taxonomy, classification and phylogeny, as well as trends in species circumscription, molecular targets and analytical methods are discussed for each of the three major parasitic groups. A by-product of this effort has been an ever increasing number of parasitic flatworms characterized genetically, and the useful application of these data to the diagnosis of animal and human pathogens, and to the elucidation of life histories are presented. The final section considers future directions in the field, including taxon sampling, molecular targets of choice, and the current and future utility of mitochondrial and nuclear genomics in systematic study.
Topics: Animals; Cestoda; Cestode Infections; DNA, Helminth; Genetic Markers; Genetic Variation; Genomics; Molecular Biology; Phylogeny; Platyhelminths; Species Specificity; Trematoda; Trematode Infections
PubMed: 16230104
DOI: 10.1016/S0065-308X(05)60003-6