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57-440: 381677 ENSG00000128564 ENSMUSG00000037428 O15240 Q0VGU4 NM_003378 NM_001039385 NP_003369 NP_001034474 VGF or VGF nerve growth factor inducible is a secreted protein and neuropeptide precursor that may play a role in regulating energy homeostasis, metabolism and synaptic plasticity . The protein was first discovered in 1985 by Levi et al . in an experiment with PC12 cells and its name
114-504: A functional-morphology model, all or most animals are descended from a gallertoid , a free-living ( pelagic ) sphere in seawater, consisting of a single ciliated layer of cells supported by a thin, noncellular separating layer, the basal lamina . The interior of the sphere is filled with contractile fibrous cells and a gelatinous extracellular matrix . Both the modern Placozoa and all other animals then descended from this multicellular beginning stage via two different processes: While
171-404: A hypothesis that Trichoplax is not a distinct animal but that it is a form of the planula larva of the anemone -like hydrozoan Eleutheria krohni . Although this was refuted in print by Schulze and others, Krumbach's analysis became the standard textbook explanation, and nothing was printed in zoological journals about Trichoplax until the 1960s. The development of electron microscopy in
228-546: A marginal level of statistical significance. A concept based on purely morphological characteristics pictures the Placozoa as the nearest relative of the animals with true tissues ( Eumetazoa ). The taxon they share, called the Epitheliozoa , is itself construed to be a sister group to the sponges ( Porifera ): Porifera Placozoa Eumetazoa The above view could be correct, although there
285-675: A primitive metazoan phylum. The first known placozoan, Trichoplax adhaerens , was discovered in 1883 by the German zoologist Franz Eilhard Schulze (1840–1921). Describing the uniqueness, another German, Karl Gottlieb Grell (1912–1994), erected a new phylum, Placozoa, for it in 1971. Remaining a monotypic phylum for over a century, new species began to be added since 2018. So far, three other extant species have been described, in two distinct classes: Uniplacotomia ( Hoilungia hongkongensis in 2018 and Cladtertia collaboinventa in 2022 ) and Polyplacotomia ( Polyplacotoma mediterranea ,
342-438: A relationship comes from special cell to cell junctions – belt desmosomes – that occur not just in the Placozoa but in all animals except the sponges: They enable the cells to join together in an unbroken layer like the epitheloid of the Placozoa. Trichoplax adhaerens also shares the ventral gland cells with most eumetazoans. Both characteristics can be considered evolutionarily derived features ( apomorphies ), and thus form
399-473: A similar method to try and isolate acetylcholine but instead discovered a peptide substance that induced physiological changes including muscle contractions and depressed blood pressure. These effects were not abolished using atropine, ruling out the substance as acetylcholine. In insects, proctolin was the first neuropeptide to be isolated and sequenced. In 1975, Alvin Starratt and Brian Brown extracted
456-473: A single-celled Amoeba , it has no regular outline, although the lower surface is somewhat concave, and the upper surface is always flattened. The body consists of an outer layer of simple epithelium enclosing a loose sheet of stellate cells resembling the mesenchyme of some more complex animals. The epithelial cells bear cilia , which the animal uses to help it creep along the seafloor. The lower surface engulfs small particles of organic detritus, on which
513-617: A small amount of neuropeptide (3 - 10mM) compared to synaptic vesicles containing neurotransmitters (e.g. 100mM for acetylcholine). Evidence shows that neuropeptides are released after high-frequency firing or bursts, distinguishing dense core vesicle from synaptic vesicle release. Neuropeptides utilize volume transmission and are not reuptaken quickly, allowing diffusion across broad areas (nm to mm) to reach targets. Almost all neuropeptides bind to G protein-coupled receptors (GPCRs), inducing second messenger cascades to modulate neural activity on long time-scales. Expression of neuropeptides in
570-440: A subset of neurons in the central and peripheral nervous systems and specific populations of endocrine cells in the adenohypophysis , adrenal medulla , gastrointestinal tract, and pancreas . VGF expression is induced by NGF , CREB and BDNF and regulated by neurotrophin-3 . Physical exercise significantly increases VGF expression in mice hippocampal tissue and upregulates a neurotrophic signaling cascade thought to underlie
627-547: A way similar to the neuropeptides of higher animals. Peptide signals play a role in information processing that is different from that of conventional neurotransmitters, and many appear to be particularly associated with specific behaviours. For example, oxytocin and vasopressin have striking and specific effects on social behaviours, including maternal behaviour and pair bonding. CCAP has several functions including regulating heart rate, allatostatin and proctolin regulate food intake and growth, bursicon controls tanning of
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#1732782993431684-492: Is Latin meaning "adherent", reflecting its propensity to stick to the glass slides and pipettes used in its examination. Schulze realized that the animal could not be a member of any existing phyla, and based on the simple structure and behaviour, concluded in 1891 that it must be an early metazoan. He also observed the reproduction by fission, cell layers and locomotion. In 1893, Italian zoologist Francesco Saverio Monticelli described another animal which he named Treptoplax ,
741-405: Is a phylum of marine and free-living (non-parasitic) animals. They are blob-like animals composed of aggregations of cells. Moving in water by ciliary motion , eating food by engulfment , reproducing by fission or budding , placozoans are described as "the simplest animals on Earth." Structural and molecular analyses have supported them as among the most basal animals, thus, constituting
798-547: Is a list of neuroactive peptides co-released with other neurotransmitters. Transmitter names are shown in bold. Norepinephrine (noradrenaline). In neurons of the A2 cell group in the nucleus of the solitary tract ), norepinephrine co-exists with: GABA Acetylcholine Dopamine Epinephrine (adrenaline) Serotonin (5-HT) Some neurons make several different peptides. For instance, vasopressin co-exists with dynorphin and galanin in magnocellular neurons of
855-399: Is non- acronymic . VGF gene encodes a precursor which is divided by proteolysis to polypeptides of different mass, which have a variety of functions, the best studied of which are the roles of TLQP-21 in the control of appetite and inflammation, and TLQP-62 as well as AQEE-30 in regulating depression-like behaviors and memory. The expression of VGF and VGF-derived peptides is detected in
912-507: Is released, yielding fast and rapid excitation of the muscle. At high frequency activation however, dense core vesicles release proctolin, inducing prolonged contractions. Thus, neuropeptide release can be fine-tuned to modulate synaptic activity in certain contexts. Some regions of the nervous system are specialized to release distinctive sets of peptides. For example, the hypothalamus and the pituitary gland release peptides (e.g. TRH, GnRH, CRH, SST) that act as hormones In one subpoplation of
969-1047: Is some evidence that neuropeptides bind to other receptor targets. Peptide-gated ion channels (FMRFamide-gated sodium channels) have been found in snails and Hydra. Other examples of non-GPCR targets include: insulin-like peptides and tyrosine-kinase receptors in Drosophila and atrial natriuretic peptide and eclosion hormone with membrane-bound guanylyl cyclase receptors in mammals and insects. Due to their modulatory and diffusive nature, neuropeptides can act on multiple time and spatial scales. Below are some examples of neuropeptide actions: Neuropeptides are often co-released with other neurotransmitters and neuropeptides to modulate synaptic activity. Synaptic vesicles and dense core vesicles can have differential activation properties for release, resulting in context-dependent co-release combinations. For example, insect motor neurons are glutamatergic and some contain dense core vesicles with proctolin . At low frequency activation, only glutamate
1026-526: Is some evidence that the ctenophores , traditionally seen as Eumetazoa , may be the sister to all other animals. This is now a disputed classification. Placozoans are estimated to have emerged 750–800 million years ago, and the first modern neuron to have originated in the common ancestor of cnidarians and bilaterians about 650 million years ago (many of the genes expressed in modern neurons are absent in ctenopheres, although some of these missing genes are present in placozoans). The principal support for such
1083-520: Is that it leaves morphological features of the animals completely out of consideration. The extreme degree of simplification that would have to be postulated for the Placozoa in this model, moreover, is only known for parasitic organisms, but would be difficult to explain functionally in a free-living species like Trichoplax adhaerens . This version is supported by statistical analysis of the Trichoplax adhaerens whole genome sequence in comparison to
1140-408: Is the precursor to the external skin layer ( epidermis ), among other things. The interior space pervaded by a fiber syncytium in the Placozoa would then correspond to connective tissue in the other animals. It is unclear whether the calcium ions stored in the syncytium would be related to the lime skeletons of many cnidarians. As noted above, this hypothesis was supported in a statistical analysis of
1197-463: Is the thickest made up of numerous fiber cells, which contain mitochondrial complexes, vacuoles and endosymbiotic bacteria in the endoplasmic reticulum . The lower epithelium consists of numerous monociliated cylinder cells along with a few endocrine-like gland cells and lipophil cells. Each lipophil cell contains numerous middle-sized granules, one of which is a secretory granule . The body axes of Hoilungia and Trichoplax are overtly similar to
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#17327829934311254-575: The Bilateria . Currently, they are typically placed according to the cladogram below: Porifera Ctenophora Placozoa Cnidaria Bilateria / Triploblasts In this cladogram the Epitheliozoa and Eumetazoa are synonyms to each other and to the Diploblasts , and the Ctenophora are basal to them. An argument raised against the proposed scenario
1311-623: The Cnidaria and once in the Bilateria . If they branched off before the Cnidaria and Bilateria split, the neurons and muscles would have the same origin in the two latter groups. On the basis of their simple structure, the Placozoa were frequently viewed as a model organism for the transition from unicellular organisms to the multicellular animals ( Metazoa ) and are thus considered a sister taxon to all other metazoans: Placozoa Sponges (Porifera) Animals with tissues (Eumetazoa) According to
1368-433: The Trichoplax adhaerens whole genome sequence, as compared to the whole-genome sequences of six other animals and two related non-animal species. A third hypothesis, based primarily on molecular genetics, views the Placozoa as highly simplified eumetazoans . According to this, Trichoplax adhaerens is descended from considerably more complex animals that already had muscles and nerve tissues. Both tissue types, as well as
1425-456: The arcuate nucleus of the hypothalamus , three anorectic peptides are co-expressed: α-melanocyte-stimulating hormone (α-MSH), galanin-like peptide , and cocaine-and-amphetamine-regulated transcript (CART), and in another subpopulation two orexigenic peptides are co-expressed, neuropeptide Y and agouti-related peptide (AGRP). These peptides are all released in different combinations to signal hunger and satiation cues. The following
1482-731: The supraoptic nucleus and paraventricular nucleus , and with CRF (in parvocellular neurons of the paraventricular nucleus ) Oxytocin in the supraoptic nucleus co-exists with enkephalin , dynorphin , cocaine-and amphetamine regulated transcript (CART) and cholecystokinin . Peptides are ancient signaling systems that are found in almost all animals on Earth. Genome sequencing reveals evidence of neuropeptide genes in Cnidaria , Ctenophora , and Placozoa , some of oldest living animals with nervous systems or neural-like tissues. Recent studies also show genomic evidence of neuropeptide processing machinery in metazoans and choanoflagellates , suggesting that neuropeptide signaling may predate
1539-676: The American copperhead and the West African carpet viper. The Placozoa show substantial evolutionary radiation in regard to sodium channels , of which they have 5–7 different types, more than any other invertebrate species studied to date. Three modes of population dynamics depended upon feeding sources, including induction of social behaviors, morphogenesis, and reproductive strategies. In addition to fission, representatives of all species produced “swarmers” (a separate vegetative reproduction stage), which could also be formed from
1596-476: The action of antidepressants . Changes in expression of discrete VGF fragments have been detected in different neurological and psychiatric conditions. In schizophrenia , one study has shown an increase in the VGF23-62 peptide and a subsequent small study demonstrated that drugs further increase the expression, pointing at a possible ameliorating action of the fragment. A decreased expression of VGF26-62 peptide
1653-604: The animal feeds . All placozoa can reproduce asexually, budding off smaller individuals, and the lower surface may also bud off eggs into the mesenchyme . Sexual reproduction has been reported to occur in one clade of placozoans, whose strain H8 was later found to belong to genus Cladtertia , where intergenic recombination was observed as well as other hallmarks of sexual reproduction. Some Trichoplax species contain Rickettsiales bacteria as endosymbionts . One of
1710-522: The at least 20 described species turned out to have two bacterial endosymbionts; Grellia which lives in the animal's endoplasmic reticulum and is assumed to play a role in the protein and membrane production. The other endosymbiont is the first described Margulisbacteria , that lives inside cells used for algal digestion . It appears to eat the fats and other lipids of the algae and provide its host with vitamins and amino acids in return. Studies suggest that aragonite crystals in crystal cells have
1767-415: The basal lamina of the epithelium , were accordingly lost more recently by radical secondary simplification. Various studies in this regard so far yield differing results for identifying the exact sister group: In one case the Placozoa would qualify as the nearest relatives of the Cnidaria , while in another they would be a sister group to the Ctenophora , and occasionally they are placed directly next to
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1824-482: The basis of a common taxon for all animals that possess them. One possible scenario inspired by the proposed hypothesis starts with the idea that the monociliated cells of the epitheloid in Trichoplax adhaerens evolved by reduction of the collars in the collar cells ( choanocytes ) of sponges as the hypothesized ancestors of the Placozoa abandoned a filtering mode of life. The epitheloid would then have served as
1881-488: The cuticle and corazonin has a role in cuticle pigmentation and moulting. Neuropeptides are synthesized from inactive precursor proteins called prepropeptides. Prepropeptides contain sequences for a family of distinct peptides and often contain duplicated copies of the same peptides, depending on the organism. In addition to the precursor peptide sequences, prepropeptides also contain a signal peptide, spacer peptides, and cleavage sites. The signal peptide sequence guides
1938-487: The development of nervous tissues. Additionally, Ctenophore and Placozoa neural signaling is entirely peptidergic and lacks the major amine neurotransmitters such as acetylcholine, dopamine, and serotonin. This also suggests that neuropeptide signaling developed before amine neurotransmitters. In the early 1900s, chemical messengers were crudely extracted from whole animal brains and tissues and studied for their physiological effects. In 1931, von Euler and Gaddum, used
1995-629: The gut, muscles, and heart. Neuropeptides are synthesized from large precursor proteins which are cleaved and post-translationally processed then packaged into large dense core vesicles . Neuropeptides are often co-released with other neuropeptides and neurotransmitters in a single neuron, yielding a multitude of effects. Once released, neuropeptides can diffuse widely to affect a broad range of targets. Neuropeptides are extremely ancient and highly diverse chemical messengers. Placozoans such as Trichoplax , extremely basal animals which do not possess neurons, use peptides for cell-to-cell communication in
2052-556: The lower epithelium with greater cell-type diversity. There is no convincing fossil record of the placozoa, although the Ediacaran biota (Precambrian, 550 million years ago ) organism Dickinsonia appears somewhat similar to placozoans. Knaust (2021) reported preservation of placozoan fossils in a microbialite bed from the Middle Triassic Muschelkalk ( Germany ). Traditionally, classification
2109-467: The mid-20th century allowed in-depth observation of the cellular components of organisms, following which there was renewed interest in Trichoplax starting in 1966. The most important descriptions were made by Karl Gottlieb Grell at the University of Tübingen since 1971. That year, Grell revived Schulze's interpretation that the animals are unique and created a new phylum Placozoa. Grell derived
2166-647: The most basal, in 2019 ). A single putative fossil species is known, the Middle Triassic Maculicorpus microbialis . Trichoplax was discovered in 1883 by the German zoologist Franz Eilhard Schulze , in a seawater aquarium at the Zoological Institute in Graz, Austria . The generic name is derived from the classical Greek θρίξ ( thrix ), meaning "hair", and πλάξ ( plax ), "plate". The specific epithet adhaerens
2223-412: The most reliable approximation of the placozoans' phylogeny. Their exact position on the phylogenetic tree would give important information about the origin of neurons and muscles. If the absence of these features is an original trait of the Placozoa, it would mean that a nervous system and muscles evolved three times should placozoans and cnidarians be a sister group ; once in the Ctenophora , once in
2280-683: The name from the placula hypothesis, Otto Bütschli 's notion on the origin of metazoans . Placozoans do not have well-defined body plan, much like amoebas , unicellular eukaryotes. As Andrew Masterson reported: "they are as close as it is possible to get to being simply a little living blob." An individual body measures about 0.55 mm in diameter. There are no body parts; as one of the researchers Michael Eitel described: "There's no mouth, there's no back, no nerve cells, nothing." Animals studied in laboratories have bodies consisting of everything from hundreds to millions of cells. Placozoans have only three anatomical parts as tissue layers inside its body:
2337-539: The nervous system is diverse. Neuropeptides are often co-released with other neuropeptides and neurotransmitters, yielding a diversity of effects depending on the combination of release. For example, vasoactive intestinal peptide is typically co-released with acetylcholine. Neuropeptide release can also be specific. In Drosophila larvae, for example, eclosion hormone is expressed in just two neurons. Most neuropeptides act on G-protein coupled receptors (GPCRs). Neuropeptide-GPCRs fall into two families: rhodopsin-like and
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2394-462: The neuron and can release peptides at the synaptic cleft, cell body, and along the axon. Neuropeptides are released by dense core vesicles after depolarization of the cell. Compared to classical neurotransmitter signaling, neuropeptide signaling is more sensitive. Neuropeptide receptor affinity is in the nanomolar to micromolar range while neurotransmitter affinity is in the micromolar to millimolar range. Additionally, dense core vesicles contain
2451-448: The oldest branch of the multicellular animals, and a relic of the Ediacaran fauna , or even the pre-Ediacara fauna. Although very successful in their ecological niche , due to the absence of extracellular matrix and basal lamina , the development potential of these animals was of course limited, which would explain the low rate of evolution of their phenotype (their outward form as adults) – referred to as bradytely . This hypothesis
2508-494: The oral–aboral axis of cnidarians , animals from another phylum with which they are most closely related. Structurally, they can not be distinguished from other placozoans, so that identification is purely on genetic (mitochondrial DNA) differences. Genome sequencing has shown that each species has a set of unique genes and several uniquely missing genes. Trichoplax is a small, flattened, animal around 1 mm (0.039 in) across. An amorphous multi-celled body, analogous to
2565-522: The peptide from hindgut muscles of the cockroach and found that its application enhanced muscle contractions. While Starratt and Brown initially thought of proctolin as an excitatory neurotransmitter, proctolin was later confirmed as a neuromodulatory peptide. David de Wied first used the term "neuropeptide" in the 1970s to delineate peptides derived from the nervous system. Placozoa Placozoa ( / ˌ p l æ k ə ˈ z oʊ ə / PLAK -ə- ZOH -ə ; lit. ' flat animals ' )
2622-554: The precursor to the true epithelial tissue of the eumetazoans. In contrast to the model based on functional morphology described earlier, in the Epitheliozoa hypothesis, the ventral and dorsal cell layers of the Placozoa are homologs of endoderm and ectoderm — the two basic embryonic cell layers of the eumetazoans. The digestive gastrodermis in the Cnidaria or the gut epithelium in the bilaterally symmetrical animals ( Bilateria ) may have developed from endoderm, whereas ectoderm
2679-427: The probability of encountering food, potential sexual partners, or predators is the same in all directions for animals floating freely in the water, there is a clear difference on the seafloor between the functions useful on body sides facing toward and away from the substrate , leading their sensory, defensive, and food-gathering cells to differentiate and orient according to the vertical – the direction perpendicular to
2736-518: The protein to the secretory pathway, starting at the endoplasmic reticulum . The signal peptide sequence is removed in the endoplasmic reticulum, yielding a propeptide. The propeptide travels to the Golgi apparatus where it is proteolytically cleaved and processed into multiple peptides. Peptides are packaged into dense core vesicles, where further cleaving and processing, such as C-terminal amidation, can occur. Dense core vesicles are transported throughout
2793-466: The same function as statoliths, allowing it to use gravity for spatial orientation . Located in the dorsal epithelium there are lipid granules called shiny spheres which release a cocktail of venoms and toxins as an anti-predator defense, and can induce paralysis or death in some predators. Genes has been found in Trichoplax with a strong resemblance to the venom genes of some poisonous snakes, like
2850-508: The secretin class. Most peptides activate a single GPCR, while some activate multiple GPCRs (e.g. AstA, AstC, DTK). Peptide-GPCR binding relationships are highly conserved across animals. Aside from conserved structural relationships, some peptide-GPCR functions are also conserved across the animal kingdom. For example, neuropeptide F/neuropeptide Y signaling is structurally and functionally conserved between insects and mammals. Although peptides mostly target metabotropic receptors, there
2907-439: The specimens of which he collected from Naples. He gave the species name T. reptans in 1896. Monticelli did not preserve them and no other specimens were found again, as a result of which the identification is ruled as doubtful, and the species rejected. Schulze's description was opposed by other zoologists. For instance, in 1890, F.C. Noll argued that the animal was a flat worm (Turbellaria). In 1907, Thilo Krumbach published
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#17327829934312964-418: The substrate. In the proposed functional-morphology model, the Placozoa, and possibly several similar organisms only known from the fossils, are descended from such a life form, which is now termed placuloid . Three different life strategies have accordingly led to three different possible lines of development: Should any of the analyses presented above turn out to be correct, Trichoplax adhaerens would be
3021-410: The upper, intermediate (middle) and lower epithelia . There are at least six different cell types. The upper epithelium is the thinnest portion and essentially comprises flat cells with their cell body hanging underneath the surface, and each cell having a cilium . Crystal cells are sparsely distributed near the marginal edge. A few cells have unusually large number of mitochondria . The middle layer
3078-506: The whole genome sequences of six other animals and two related non-animal species. However, Ctenophora was not included in the analyses, placing the placozoans outside of the sampled Eumetazoans. DNA comparisons suggest that placozoans are related to Cnidaria , derived from planula larva (as seen in some Cnidaria). The Bilateria also are thought to be derived from planuloids. The Cnidaria and Placozoa body axis are overtly similar, and placozoan and cnidarian cells are responsive to
3135-501: Was based on their level of organization, i.e., they possess no tissues or organs. However this may be as a result of secondary loss and thus is inadequate to exclude them from relationships with more complex animals. More recent work has attempted to classify them based on the DNA sequences in their genome; this has placed the phylum between the sponges and the eumetazoa . In such a feature-poor phylum, molecular data are considered to provide
3192-815: Was found in frontotemporal dementia and the expression of a fragment containing aminoacids 378-398 was found to be changing in amyotrophic lateral sclerosis and Alzheimer's disease . VGF expression has also been shown in damaged peripheral nerves, and it is thought to have a role in neuropathic pain . In glioblastoma , VGF has been shown to play autocrine and paracrine roles in feedback loops between differentiated glioblastoma cells and glioblastoma-specific cancer stem cells , promoting growth, survival and self-renewal. Neuropeptide Neuropeptides are chemical messengers made up of small chains of amino acids that are synthesized and released by neurons . Neuropeptides typically bind to G protein-coupled receptors (GPCRs) to modulate neural activity and other tissues like
3249-402: Was supported by a recent analysis of the Trichoplax adhaerens mitochondrial genome in comparison to those of other animals. The hypothesis was, however, rejected in a statistical analysis of the Trichoplax adhaerens whole genome sequence in comparison to the whole genome sequences of six other animals and two related non-animal species, but only at the p = 0.07 level, which indicates
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