Novel Cell Types, Neurosecretory Cells, and Body Plan of the Early-Diverging Metazoan Trichoplax adhaerens
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Background Trichoplax adhaerens is the best-known member of the phylum Placozoa, one of the earliest-diverging metazoan phyla. It is a small disk-shaped animal that glides on surfaces in warm oceans to feed on algae. Prior anatomical studies of Trichoplax revealed that it has a simple three-layered organization with four somatic cell types.Results We reinvestigate the cellular organization of Trichoplax using advanced freezing and microscopy techniques to identify localize and count cells. Six somatic cell types are deployed in stereotyped positions. A thick ventral plate, comprising the majority of the cells, includes ciliated epithelial cells, newly identified lipophil cells packed with large lipid granules, and gland cells. Lipophils project deep into the interior, where they alternate with regularly spaced fiber cells whose branches contact all other cell types, including cells of the dorsal and ventral epithelium. Crystal cells, each containing a birefringent crystal, are arrayed around the rim. Gland cells express several proteins typical of neurosecretory cells, and a subset of them, around the rim, also expresses an FMRFamide-like neuropeptide.Conclusions Structural analysis of Trichoplax with significantly improved techniques provides an advance in understanding its cell types and their distributions. We find two previously undetected cell types, lipohil and crystal cells, and an organized body plan in which different cell types are arranged in distinct patterns. The composition of gland cells suggests that they are neurosecretory cells and could control locomotor and feeding behavior.
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Newly identified 'lipophil' cells are characterized by a larger number of smaller vesicles, and a single large inclusion at the apical side with an acidic and lipophilic content.
“Instead, newly identified ‘lipophil’ cells are characterized by a larger number of smaller vesicles, and a single large inclusion at the apical side with an acidic and lipophilic content (Fig. 2d) (Smith et al. 2015; Smith et al. 2014).”
From A non-bilaterian perspective on the development and evolution of animal digestive systems (2019) · cites this paper as Smith et al. 2014
This long period of rudimentary nervous system development likely involved the deployment of genes now associated with the nervous system in proto-nervous system tissues, similar to Trichoplax today.
“This long period of rudimentary nervous system development likely involved the deployment of genes now associated with the nervous system in proto-nervous system tissues, similar to Trichoplax today [13,53,58].”
From Early metazoan life: divergence, environment and ecology (2015) · cites this paper as [58]
Trichoplax has neurosecretory cells concentrated in the periphery of the ventral epithelium that express typical neural proteins including syntaxin, synapsin, synaptobrevin and a FMRFamide-like neuropeptide.
“While Trichoplax has no obvious neurons, it does have neurosecretory cells concentrated in the periphery of the ventral epithelium [50]. These cells express typical neural proteins including syntaxin, synapsin, synaptobrevin and a FMRFamide-like neuropeptide [47].”
From Where is my mind? How sponges and placozoans may have lost neural cell types (2015) · cites this paper as [47]
Trichoplax is thought to consist of six different cell types, none of which present an obvious similarity to a neural cell type.
“Trichoplax is thought to consist of six different cell types, none of which present an obvious similarity to a neural cell type [47].”
From Where is my mind? How sponges and placozoans may have lost neural cell types (2015) · cites this paper as [47]
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- Authors
- Smith, C. L., Varoqueaux, F., Kittelmann, M., Azzam, R. N., Cooper, B., Winters, C. A., Eitel, M., Fasshauer, D., & Reese, T. S.
- Affiliations
- National Institutes of Health (US)
- Max Planck Institute of Experimental Medicine (DE)
- University of Veterinary Medicine Hannover, Foundation (DE)
- University of Lausanne (CH)
- Corresponding author
- Smith, Carolyn L.
- Fasshauer, Dirk
- ORCID
- Venue
- Current Biology
- Publisher
- Elsevier BV
- Published
- 2014-07
- Volume
- 24
- Issue
- 14
- Pages
- 1565-1572
- ISSN
- 0960-9822 (ISSN-L)
- PMC
- PMC4128346
- OpenAlex
- W2158723722
- Cited by
- 254
- References
- 43
- Citations by year
- 2026: 7 · 2025: 26 · 2024: 22 · 2023: 21 · 2022: 16 · 2021: 34 · 2020: 16 · 2019: 27 · 2018: 21 · 2017: 19 · 2016: 17 · 2015: 22 · 2014: 6
- FWCI
- 15.58
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Licence
- Locations
- Current Biology (publishedVersion)
- PubMed (publishedVersion)
- PubMed Central (acceptedVersion)
- IRIS (submittedVersion)
- Max Planck Institute for Plasma Physics (submittedVersion)
- MPG.PuRe (Max Planck Society) (submittedVersion)
- SERVAL (Université de Lausanne) (submittedVersion, other-oa)
- Funders
- National Institutes of Health (Z99 NS999999)
- Topics
- Physical Sciences › Earth and Planetary Sciences › Paleontology › Marine Invertebrate Physiology and Ecology
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Planarian Biology and Electrostimulation
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Developmental Biology and Gene Regulation
- Keywords
- Trichoplax adhaerens, Placozoa, cell types, neurosecretory cells, body plan, crystal cells, gland cells, ciliated epithelium, fiber cells, early-diverging metazoans, cell localization
- MeSH terms
- Animals, Cytoplasmic Granules, Epithelial Cells, Epithelium, Neurons, Neurosecretion, Placozoa
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