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1.
Nat Methods ; 21(4): 543-545, 2024 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-38609555

Assuntos
Placozoa , Animais
2.
Methods Mol Biol ; 2757: 491-508, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38668980

RESUMO

Transcription factors (TFs) play a pivotal role as regulators of gene expression, orchestrating the formation and maintenance of diverse animal body plans and innovations. However, the precise contributions of TFs and the underlying mechanisms driving the origin of basal metazoan body plans, particularly in ctenophores, remain elusive. Here, we present a comprehensive catalog of TFs in 2 ctenophore species, Pleurobrachia bachei and Mnemiopsis leidyi, revealing 428 and 418 TFs in their respective genomes. In contrast, morphologically simpler metazoans have a reduced TF representation compared to ctenophores, cnidarians, and bilaterians: the sponge Amphimedon encodes 277 TFs, and the placozoan Trichoplax adhaerens encodes 274 TFs. The emergence of complex ctenophore tissues and organs coincides with significant lineage-specific diversification of the zinc finger C2H2 (ZF-C2H2) and homeobox superfamilies of TFs. Notable, the lineages leading to Amphimedon and Trichoplax exhibit independent expansions of leucine zipper (BZIP) TFs. Some lineage-specific TFs may have evolved through the domestication of mobile elements, thereby supporting alternative mechanisms of parallel TF evolution and body plan diversification across the Metazoa.


Assuntos
Ctenóforos , Evolução Molecular , Filogenia , Fatores de Transcrição , Animais , Fatores de Transcrição/metabolismo , Fatores de Transcrição/genética , Ctenóforos/genética , Ctenóforos/metabolismo , Genoma , Placozoa/genética , Placozoa/metabolismo
3.
Methods Mol Biol ; 2757: 531-581, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38668982

RESUMO

Experimental discovery of neuropeptides and peptide hormones is a long and tedious task. Mining the genomic and transcriptomic sequence data with robust secretory peptide prediction tools can significantly facilitate subsequent experiments. We describe the application of various in silico neuropeptide discovery methods for the placozoan Trichopax adhaerens as an illustrated example and a powerful experimental paradigm for cellular and evolutionary biology. In total, 33 placozoan (neuro)peptide-like hormone precursors were found using homology-based BLAST search and repeat-based and comparative evolutionary methods. Some of the discovered precursors are homologous to insulins and RFamide precursors from Cnidaria and other animal phyla.


Assuntos
Biologia Computacional , Neuropeptídeos , Placozoa , Animais , Biologia Computacional/métodos , Placozoa/genética , Neuropeptídeos/genética , Neuropeptídeos/metabolismo , Sequência de Aminoácidos , Filogenia , Evolução Molecular
4.
Methods Mol Biol ; 2757: 509-529, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38668981

RESUMO

The phylum Placozoa remains one of the least explored among early-branching metazoan lineages. For over 130 years, this phylum had been represented by the single species Trichoplax adhaerens-an animal with the simplest known body plan (three cell layers without any organs) but complex behaviors. Recently, extensive sampling of placozoans across the globe and their subsequent genetic analysis have revealed incredible biodiversity with numerous cryptic species worldwide. However, only a few culture protocols are available to date, and all are for one species only. Here, we describe the breeding of four different species representing two placozoan genera: Trichoplax adhaerens, Trichoplax sp. H2, Hoilungia sp. H4, and Hoilungia hongkongensis originating from diverse biotopes. Our protocols allow to culture all species under comparable conditions. Next, we outlined various food sources and optimized strain-specific parameters enabling long-term culturing. These protocols can facilitate comparative analyses of placozoan biology and behaviors, which together will contribute to deciphering general principles of animal organization.


Assuntos
Placozoa , Animais , Placozoa/genética
5.
Methods Mol Biol ; 2757: 103-122, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38668963

RESUMO

Placozoans are morphologically the simplest free-living animals. They represent a unique window of opportunities to understand both the origin of the animal organization and the rules of life for the system and synthetic biology of the future. However, despite more than 100 years of their investigations, we know little about their organization, natural habitats, and life strategies. Here, we introduce this unique animal phylum and highlight some directions vital to broadening the frontiers of the biomedical sciences. In particular, understanding the genomic bases of placozoan biodiversity, cell identity, connectivity, reproduction, and cellular bases of behavior are critical hot spots for future studies.


Assuntos
Placozoa , Animais , Placozoa/genética , Biodiversidade , Filogenia , Genoma , Genômica/métodos , Reprodução , Ecossistema
6.
Mol Biol (Mosk) ; 57(5): 895-897, 2023.
Artigo em Russo | MEDLINE | ID: mdl-37752654

RESUMO

The marine free-living organism Trichoplax (phylum Placozoa) resembles a unicellular amoeba in shape and type of movement. Trichoplax diverged from the main evolutionary tree in the Neoproterozoic Era. Trichoplax provides one of the simplest models of multicellular animals and a strong example of how cells of an organism interact to form an ensemble during its development and movement. Two orthologs of the mouse Piezo1 protein (6B3R) were found in two Trichoplax haplotypes, H1 and H2, as a result of a search for similar sequences in the NCBI databases. Spatial models of the respective proteins XP_002112008.1 and RDD46920.1 were created via a structural alignment with 6KG7 (mouse Piezo2) template. Their domain structures were analyzed, and a limited graph of protein-protein interactions was constructed for the hypothetical mechanosensor XP_002112008.1. The possibility of signal transduction from the mechanoreceptor to membrane complexes, the cytoplasm, and the cell nucleus was shown. Trichoplax mechanoreceptors were assumed to play a role in perception of force stimuli from neighbor cells and the environment. Based on the results, the primitive Trichoplax organism was proposed as the simplest multicellular model of mechanical and morphogenetic movements.


Assuntos
Placozoa , Animais , Camundongos , Placozoa/genética , Mapas de Interação de Proteínas , Citoplasma , Canais Iônicos/genética
7.
Commun Biol ; 6(1): 951, 2023 09 18.
Artigo em Inglês | MEDLINE | ID: mdl-37723223

RESUMO

ASIC channels are bilaterian proton-gated sodium channels belonging to the large and functionally-diverse Deg/ENaC family that also includes peptide- and mechanically-gated channels. Here, we report that the non-bilaterian invertebrate Trichoplax adhaerens possesses a proton-activated Deg/ENaC channel, TadNaC2, with a unique combination of biophysical features including tachyphylaxis like ASIC1a, reduced proton sensitivity like ASIC2a, biphasic macroscopic currents like ASIC3, as well as low sensitivity to the Deg/ENaC channel blocker amiloride and Ca2+ ions. Structural modeling and mutation analyses reveal that TadNaC2 proton gating is different from ASIC channels, lacking key molecular determinants, and involving unique residues within the palm and finger regions. Phylogenetic analysis reveals that a monophyletic clade of T. adhaerens Deg/ENaC channels, which includes TadNaC2, is phylogenetically distinct from ASIC channels, instead forming a clade with BASIC channels. Altogether, this work suggests that ASIC-like channels evolved independently in T. adhaerens and its phylum Placozoa. Our phylogenetic analysis also identifies several clades of uncharacterized metazoan Deg/ENaC channels, and provides phylogenetic evidence for the existence of Deg/ENaC channels outside of Metazoa, present in the gene data of select unicellular heterokont and filasterea-related species.


Assuntos
Placozoa , Animais , Placozoa/genética , Filogenia , Prótons , Canais Iônicos Sensíveis a Ácido/genética , Amilorida
8.
Integr Comp Biol ; 63(6): 1442-1454, 2023 Dec 29.
Artigo em Inglês | MEDLINE | ID: mdl-37355780

RESUMO

In animals, epithelial tissues are barriers against the external environment, providing protection against biological, chemical, and physical damage. Depending on the organism's physiology and behavior, these tissues encounter different types of mechanical forces and need to provide a suitable adaptive response to ensure success. Therefore, understanding tissue mechanics in different contexts is an important research area. Here, we review recent tissue mechanics discoveries in three early divergent non-bilaterian systems-Trichoplax adhaerens, Hydra vulgaris, and Aurelia aurita. We highlight each animal's simple body plan and biology and unique, rapid tissue remodeling phenomena that play a crucial role in its physiology. We also discuss the emergent large-scale mechanics in these systems that arise from small-scale phenomena. Finally, we emphasize the potential of these non-bilaterian animals to be model systems in a bottom-up approach for further investigation in tissue mechanics.


Assuntos
Epitélio , Hydra , Placozoa , Cifozoários , Animais , Epitélio/fisiologia , Placozoa/fisiologia , Cifozoários/fisiologia , Hydra/fisiologia
9.
Proc Natl Acad Sci U S A ; 120(11): e2206163120, 2023 03 14.
Artigo em Inglês | MEDLINE | ID: mdl-36897970

RESUMO

How collectives remain coordinated as they grow in size is a fundamental challenge affecting systems ranging from biofilms to governments. This challenge is particularly apparent in multicellular organisms, where coordination among a vast number of cells is vital for coherent animal behavior. However, the earliest multicellular organisms were decentralized, with indeterminate sizes and morphologies, as exemplified by Trichoplax adhaerens, arguably the earliest-diverged and simplest motile animal. We investigated coordination among cells in T. adhaerens by observing the degree of collective order in locomotion across animals of differing sizes and found that larger individuals exhibit increasingly disordered locomotion. We reproduced this effect of size on order through a simulation model of active elastic cellular sheets and demonstrate that this relationship is best recapitulated across all body sizes when the simulation parameters are tuned to a critical point in the parameter space. We quantify the trade-off between increasing size and coordination in a multicellular animal with a decentralized anatomy that shows evidence of criticality and hypothesize as to the implications of this on the evolution hierarchical structures such as nervous systems in larger organisms.


Assuntos
Placozoa , Animais , Placozoa/fisiologia , Tamanho Corporal , Sistema Nervoso Central , Evolução Biológica
10.
Front Endocrinol (Lausanne) ; 13: 973862, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-36213267

RESUMO

Bilateria have bilateral symmetry and are subdivided into Deuterostomia (animals like vertebrates) and Protostomia (animals like insects and mollusks). Neuropeptides occur in both Proto- and Deuterostomia and they are frequently structurally related across these two lineages. For example, peptides belonging to the oxytocin/vasopressin family exist in both clades. The same is true for the G protein-coupled receptors (GPCRs) of these peptides. These observations suggest that these neuropeptides and their GPCRs were already present in the common ancestor of Proto- and Deuterostomia, which lived about 700 million years ago (MYA). Furthermore, neuropeptides and their GPCRs occur in two early-branching phyla that diverged before the emergence of Bilateria: Cnidaria (animals like corals and sea anemones), and Placozoa (small disk-like animals, feeding on algae). The sequences of these neuropeptides and their GPCRs, however, are not closely related to those from Bilateria. In addition, cnidarian neuropeptides and their receptors are not closely related to those from Placozoa. We propose that the divergence times between Cnidaria, Placozoa, and Bilateria might be too long for recognizing sequence identities. Leucine-rich repeats-containing GPCRs (LGRs) are a special class of GPCRs that are characterized by a long N-terminus containing 10-20 leucine-rich domains, which are used for ligand binding. Among the ligands for LGRs are dimeric glycoprotein hormones, and insulin-like peptides, such as relaxin. LGRs have been found not only in Proto- and Deuterostomia, but also in early emerging phyla, such as Cnidaria and Placozoa. Humans have eight LGRs. In our current review, we have revisited the annotations of LGRs from the sea anemone Nematostella vectensis and the placozoan Trichoplax adhaerens. We identified 13 sea anemone LGRs and no less than 46 LGRs from T. adhaerens. All eight human LGRs appear to have orthologues in sea anemones and placozoans. LGRs and their ligands, therefore, have a long evolutionary history, going back to the common ancestor of Cnidaria and Placozoa.


Assuntos
Insulinas , Neuropeptídeos , Placozoa , Relaxina , Anêmonas-do-Mar , Animais , Glicoproteínas/metabolismo , Humanos , Leucina , Ligantes , Neuropeptídeos/genética , Neuropeptídeos/metabolismo , Ocitocina/metabolismo , Placozoa/genética , Placozoa/metabolismo , Receptores Acoplados a Proteínas G/genética , Receptores Acoplados a Proteínas G/metabolismo , Relaxina/metabolismo
11.
Methods Mol Biol ; 2450: 121-133, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-35359305

RESUMO

Placozoans are a promising model system to study fundamental regeneration processes in a morphologically and genetically very simple animal. We here provide a brief introduction to the enigmatic Placozoa and summarize the state of the art of animal handling and experimental manipulation possibilities.


Assuntos
Placozoa , Animais , Placozoa/genética
12.
J Biol Chem ; 298(4): 101741, 2022 04.
Artigo em Inglês | MEDLINE | ID: mdl-35182524

RESUMO

CaV1 and CaV2 voltage-gated calcium channels evolved from an ancestral CaV1/2 channel via gene duplication somewhere near the stem animal lineage. The divergence of these channel types led to distinguishing functional properties that are conserved among vertebrates and bilaterian invertebrates and contribute to their unique cellular roles. One key difference pertains to their regulation by calmodulin (CaM), wherein bilaterian CaV1 channels are uniquely subject to pronounced, buffer-resistant Ca2+/CaM-dependent inactivation, permitting negative feedback regulation of calcium influx in response to local cytoplasmic Ca2+ rises. Early diverging, nonbilaterian invertebrates also possess CaV1 and CaV2 channels, but it is unclear whether they share these conserved functional features. The most divergent animals to possess both CaV1 and CaV2 channels are placozoans such as Trichoplax adhaerens, which separated from other animals over 600 million years ago shortly after their emergence. Hence, placozoans can provide important insights into the early evolution of CaV1 and CaV2 channels. Here, we build upon previous characterization of Trichoplax CaV channels by determining the cellular expression and ion-conducting properties of the CaV1 channel orthologue, TCaV1. We show that TCaV1 is expressed in neuroendocrine-like gland cells and contractile dorsal epithelial cells. In vitro, this channel conducts dihydropyridine-insensitive, high-voltage-activated Ca2+ currents with kinetics resembling those of rat CaV1.2 but with left-shifted voltage sensitivity for activation and inactivation. Interestingly, TCaV1, but not TCaV2, exhibits buffer-resistant Ca2+/CaM-dependent inactivation, indicating that this functional divergence evolved prior to the emergence of bilaterian animals and may have contributed to their unique adaptation for cytoplasmic Ca2+ signaling within various cellular contexts.


Assuntos
Canais de Cálcio , Calmodulina , Evolução Molecular , Placozoa , Animais , Cálcio/metabolismo , Canais de Cálcio/genética , Canais de Cálcio/metabolismo , Calmodulina/genética , Calmodulina/metabolismo , Retroalimentação Fisiológica , Placozoa/classificação , Placozoa/genética , Placozoa/metabolismo , Ratos
13.
Sci Rep ; 11(1): 23343, 2021 12 02.
Artigo em Inglês | MEDLINE | ID: mdl-34857844

RESUMO

Placozoa is a phylum of non-bilaterian marine animals. These small, flat organisms adhere to the substrate via their densely ciliated ventral epithelium, which mediates mucociliary locomotion and nutrient uptake. They have only six morphological cell types, including one, fiber cells, for which functional data is lacking. Fiber cells are non-epithelial cells with multiple processes. We used electron and light microscopic approaches to unravel the roles of fiber cells in Trichoplax adhaerens, a representative member of the phylum. Three-dimensional reconstructions of serial sections of Trichoplax showed that each fiber cell is in contact with several other cells. Examination of fiber cells in thin sections and observations of live dissociated fiber cells demonstrated that they phagocytose cell debris and bacteria. In situ hybridization confirmed that fiber cells express genes involved in phagocytic activity. Fiber cells also are involved in wound healing as evidenced from microsurgery experiments. Based on these observations we conclude that fiber cells are multi-purpose macrophage-like cells. Macrophage-like cells have been described in Porifera, Ctenophora, and Cnidaria and are widespread among Bilateria, but our study is the first to show that Placozoa possesses this cell type. The phylogenetic distribution of macrophage-like cells suggests that they appeared early in metazoan evolution.


Assuntos
Evolução Biológica , Citofagocitose , Imunidade Inata , Placozoa/imunologia , Rodófitas/imunologia , Cicatrização , Animais , Filogenia
14.
PLoS Biol ; 19(11): e3001471, 2021 11.
Artigo em Inglês | MEDLINE | ID: mdl-34788294

RESUMO

Trichoplax adhaerens is the simplest multicellular animal with tissue differentiation and somatic cell turnover. Like all other multicellular organisms, it should be vulnerable to cancer, yet there have been no reports of cancer in T. adhaerens or any other placozoan. We investigated the cancer resistance of T. adhaerens, discovering that they are able to tolerate high levels of radiation damage (218.6 Gy). To investigate how T. adhaerens survive levels of radiation that are lethal to other animals, we examined gene expression after the X-ray exposure, finding overexpression of genes involved in DNA repair and apoptosis including the MDM2 gene. We also discovered that T. adhaerens extrudes clusters of inviable cells after X-ray exposure. T. adhaerens is a valuable model organism for studying the molecular, genetic, and tissue-level mechanisms underlying cancer suppression.


Assuntos
Reparo do DNA/genética , Placozoa/genética , Tolerância a Radiação/genética , Regulação para Cima/genética , Animais , Dano ao DNA/genética , Dano ao DNA/efeitos da radiação , Reparo do DNA/efeitos da radiação , Regulação da Expressão Gênica/efeitos da radiação , Placozoa/anatomia & histologia , Placozoa/efeitos da radiação , Exposição à Radiação , Análise de Sequência de DNA , Regulação para Cima/efeitos da radiação , Sequenciamento Completo do Genoma , Raios X
15.
Bioessays ; 43(10): e2100083, 2021 10.
Artigo em Inglês | MEDLINE | ID: mdl-34490659

RESUMO

The placozoan Trichoplax adhaerens has been bridging gaps between research disciplines like no other animal. As outlined in part 1, placozoans have been subject of hot evolutionary debates and placozoans have challenged some fundamental evolutionary concepts. Here in part 2 we discuss the exceptional genetics of the phylum Placozoa and point out some challenging model system applications for the best known species, Trichoplax adhaerens.


Assuntos
Placozoa , Animais , Evolução Biológica , Planeta Terra , Filogenia , Placozoa/genética
16.
Bioessays ; 43(10): e2100080, 2021 10.
Artigo em Inglês | MEDLINE | ID: mdl-34472126

RESUMO

The placozoan Trichoplax adhaerens is a tiny hairy plate and more simply organized than any other living metazoan. After its original description by F.E. Schulze in 1883, it attracted attention as a potential model for the ancestral state of metazoan organization, the "Urmetazoon". Trichoplax lacks any kind of symmetry, organs, nerve cells, muscle cells, basal lamina, and extracellular matrix. Furthermore, the placozoan genome is the smallest (not secondarily reduced) genome of all metazoan genomes. It harbors a remarkably rich diversity of genes and has been considered the best living surrogate for a metazoan ancestor genome. The phylum Placozoa presently harbors three formally described species, while several dozen "cryptic" species are yet awaiting their description. The phylogenetic position of placozoans has recently become a contested arena for modern phylogenetic analyses and view-driven claims. Trichoplax offers unique prospects for understanding the minimal requirements of metazoan animal organization and their corresponding malfunctions.


Assuntos
Placozoa , Animais , Evolução Biológica , Genoma , Filogenia , Placozoa/genética
17.
Biosystems ; 206: 104444, 2021 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-34023485

RESUMO

Placozoa remain an ancient multicellular system with a dynamic body structure where calcium ions carry out a primary role in maintaining the integrity of the entire animal. Zinc ions can compete with calcium ions adsorption. We studied the effect of zinc ions and l-cysteine molecules on the interaction of Trichoplax sp. H2 cells. The regularity of formless motion was diminished in the presence of 20-25 µM of Zn2+ ions leading to the formation of branching animal forms. Locomotor ciliated cells moved chaotically and independently of each other leaving the Trichoplax body and opening a network of fiber cells. Application of 100 µM cysteine resulted in dissociation of the plate into separate cells. The combined chemical treatment shifted the effect in a random sample of animals toward disintegration, i.e. initially leading to disorder of collective cell movement and then to total body fragmentation. Two dissociation patterns of Trichoplax plate as "expanding ring" and "bicycle wheel" were revealed. Analysis of the interaction of Ca2+ and Zn2+ ions with cadherin showed that more than half (54%) of the amino acid residues with which Ca2+ and Zn2+ ions bind are common. The contact interaction of cells covered by the cadherin molecules is important for the coordinated movements of Trichoplax organism, while zinc ions are capable to break junctions between the cells. The involvement of other players, for example, l-cysteine in the regulation of Ca2+-dependent adhesion may be critical leading to the typical dissociation of Trichoplax body like in a calcium-free environment. A hypothesis about the essential role of calcium ions in the emergence of Metazoa ancestor is proposed.


Assuntos
Ensaios de Migração Celular/métodos , Cisteína/metabolismo , Placozoa/metabolismo , Análise de Sistemas , Zinco/metabolismo , Animais , Sítios de Ligação/fisiologia , Sinalização do Cálcio/fisiologia , Células Cultivadas , Biologia Computacional/métodos , Cisteína/química , Íons , Placozoa/química , Zinco/química
18.
Cell Tissue Res ; 385(3): 623-637, 2021 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-33876313

RESUMO

From a morphological point of view, placozoans are among the most simple free-living animals. This enigmatic phylum is critical for our understanding of the evolution of animals and their cell types. Their millimeter-sized, disc-like bodies consist of only three cell layers that are shaped by roughly seven major cell types. Placozoans lack muscle cells and neurons but are able to move using their ciliated lower surface and take up food in a highly coordinated manner. Intriguingly, the genome of Trichoplax adhaerens, the founding member of the enigmatic phylum, has disclosed a surprising level of genetic complexity. Moreover, recent molecular and functional investigations have uncovered a much larger, so-far hidden cell-type diversity. Here, we have extended the microanatomical characterization of a recently described placozoan species-Hoilungia hongkongensis. In H. hongkongensis, we recognized the established canonical three-layered placozoan body plan but also came across several morphologically distinct and potentially novel cell types, among them novel gland cells and "shiny spheres"-bearing cells at the upper epithelium. Thus, the diversity of cell types in placozoans is indeed higher than anticipated.


Assuntos
Filogenia , Placozoa/ultraestrutura , Animais
19.
Philos Trans R Soc Lond B Biol Sci ; 376(1821): 20190762, 2021 03 29.
Artigo em Inglês | MEDLINE | ID: mdl-33550949

RESUMO

Transmitter signalling is the universal chemical language of any nervous system, but little is known about its early evolution. Here, we summarize data about the distribution and functions of neurotransmitter systems in basal metazoans as well as outline hypotheses of their origins. We explore the scenario that neurons arose from genetically different populations of secretory cells capable of volume chemical transmission and integration of behaviours without canonical synapses. The closest representation of this primordial organization is currently found in Placozoa, disk-like animals with the simplest known cell composition but complex behaviours. We propose that injury-related signalling was the evolutionary predecessor for integrative functions of early transmitters such as nitric oxide, ATP, protons, glutamate and small peptides. By contrast, acetylcholine, dopamine, noradrenaline, octopamine, serotonin and histamine were recruited as canonical neurotransmitters relatively later in animal evolution, only in bilaterians. Ligand-gated ion channels often preceded the establishment of novel neurotransmitter systems. Moreover, lineage-specific diversification of neurotransmitter receptors occurred in parallel within Cnidaria and several bilaterian lineages, including acoels. In summary, ancestral diversification of secretory signal molecules provides unique chemical microenvironments for behaviour-driven innovations that pave the way to complex brain functions and elementary cognition. This article is part of the theme issue 'Basal cognition: multicellularity, neurons and the cognitive lens'.


Assuntos
Comunicação Celular/fisiologia , Evolução Molecular , Neurotransmissores/química , Transdução de Sinais , Animais , Placozoa/fisiologia
20.
Philos Trans R Soc Lond B Biol Sci ; 376(1821): 20190764, 2021 03 29.
Artigo em Inglês | MEDLINE | ID: mdl-33550954

RESUMO

Discussions of the function of early nervous systems usually focus on a causal flow from sensors to effectors, by which an animal coordinates its actions with exogenous changes in its environment. We propose, instead, that much early sensing was reafferent; it was responsive to the consequences of the animal's own actions. We distinguish two general categories of reafference-translocational and deformational-and use these to survey the distribution of several often-neglected forms of sensing, including gravity sensing, flow sensing and proprioception. We discuss sensing of these kinds in sponges, ctenophores, placozoans, cnidarians and bilaterians. Reafference is ubiquitous, as ongoing action, especially whole-body motility, will almost inevitably influence the senses. Corollary discharge-a pathway or circuit by which an animal tracks its own actions and their reafferent consequences-is not a necessary feature of reafferent sensing but a later-evolving mechanism. We also argue for the importance of reafferent sensing to the evolution of the body-self, a form of organization that enables an animal to sense and act as a single unit. This article is part of the theme issue 'Basal cognition: multicellularity, neurons and the cognitive lens'.


Assuntos
Vias Eferentes/fisiologia , Fenômenos Fisiológicos do Sistema Nervoso , Propriocepção , Animais , Cnidários/fisiologia , Ctenóforos/fisiologia , Sistema Nervoso/química , Placozoa/fisiologia , Poríferos/fisiologia
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