Cellularization

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In evolutionary biology, the term cellularization (cellularisation) has been used in theories to explain the evolution of cells, for instance in the pre-cell theory, [1] [2] [3] dealing with the evolution of the first cells on this planet, and in the syncytial theory [4] attempting to explain the origin of Metazoa from unicellular organisms.

Contents

Processes of cell development in multinucleate cells (syncytium, plural syncytia) of animals and plants are also termed cellularization, often called syncytium cellularization.

Early diversification of life with Kandler's pre-cell theory Key: 1 Reductive formation of organic compounds from CO or CO2 by Me-sulfur coordinative chemistry 2 tapping of various redox energy sources and formation of primitive enzymes and templates 3 elements of a transcription and translation apparatus and loose associations 4 formation of pre-cells 5 stabilised circular or linear genomes 6 cytoplasmic membranes 7 rigid murein cell walls 8 various non-murein rigid cell walls 9 glycoproteinaceous cell envelope or glycokalyx 10 cytoskeleton 11 complex chromosomes and nuclear membrane 12 cell organelles via endosymbiosis". Kandler 1998 Early diversification of life and pre-cell theory.svg
Early diversification of life with Kandler's pre-cell theory

    Key:
1 Reductive formation of organic compounds from CO or CO2 by Me-sulfur coordinative chemistry
2 tapping of various redox energy sources and formation of primitive enzymes and templates
3 elements of a transcription and translation apparatus and loose associations
4 formation of pre-cells
5 stabilised circular or linear genomes
6 cytoplasmic membranes
7 rigid murein cell walls
8 various non-murein rigid cell walls
9 glycoproteinaceous cell envelope or glycokalyx
10 cytoskeleton
11 complex chromosomes and nuclear membrane
12 cell organelles via endosymbiosis".

The pre-cell theory

According to Otto Kandler's pre-cell theory, [1] [2] [3] early evolution of life and primordial metabolism (see Iron-Sulfur world hypothesis - metabolism first scenario, according to Wächtershäuser [5] [6] ) led to the early diversification of life through the evolution of a multiphenotypical population of pre-cells, [1] [2] [3] from which the three founder groups A, B, C and then, from them, the precursor cells (here named proto-cells) of the three domains of life [7] emerged successively. [1] [2] [3] [8]

In this scenario the three domains of life did not originate from an ancestral nearly complete “first cell“ nor a cellular organism often defined as the last universal common ancestor (LUCA [9] [10] [11] ), but from a population of evolving pre-cells. Kandler introduced the term cellularization for his concept of a successive evolution of cells by a process of evolutionary improvements. [1] [2] [3]

His concept may explain the quasi-random distribution of evolutionarily important features among the three domains and, at the same time, the existence of the most basic biochemical features (genetic code, set of protein amino acids etc.) in all three domains (unity of life), as well as the close relationship between the Archaea and the Eucarya. Kandler’s pre-cell theory is supported by Wächtershäuser. [8]

According to Kandler, the protection of fragile primordial life forms from their environment by the invention of envelopes (i.e. membranes, walls) was an essential improvement. For instance, the emergence of rigid cell walls by the invention and elaboration of peptidoglycan [12] in bacteria (domain Bacteria) may have been a prerequisite for their successful survival, radiation and colonisation of virtually all habitats of the geosphere and hydrosphere. [3]

A coevolution of the biosphere and the geosphere is suggested: “The evolving life could venture into a larger variety of habitats, even into microaerobic habitats in shallow, illuminated surface waters. The continuous changes in the physical environment on the aging and cooling Earth led to further diversification of habitats and favored opportunistic radiation of primitive life into numerous phenotypes on the basis of each of the different chemolithoautotrophies. Concomitantly, with the accumulation of organic matter derived from chemolithoautotrophic life, opportunistic and obligate heterotrophic life may also have developed”. [1] : 155f 

The details of Kandler's proposal for the early diversification of life are represented in a scheme, where numbers indicate evolutionary improvements. [3]

The syncytial theory or ciliate-acoel theory

This theory is also known as a theory of cellularization. It is a theory to explain the origin of the Metazoa. The idea was proposed by Hadži (1953) [4] and Hanson (1977). [13]

This cellularization (syncytial) theory states that metazoans evolved from a unicellular ciliate with multiple nuclei that went through cellularization. Firstly, the ciliate developed a ventral mouth for feeding and all nuclei moved to one side of the cell. Secondly, an epithelium was created by membranes forming barriers between the nuclei. In this way, a multicellular organism was created from one multinucleate cell (syncytium). [14]

Example and Criticism

Turbellarian flatworms

According to the syncytial theory, the ciliate ancestor, by several cellularization processes, evolved into the currently known turbellarian flatworms, which are therefore the most primitive metazoans. The theory of cellularization is based on the large similarities between ciliates and flatworms. Both ciliates and flatworms have cilia, are bilaterally symmetric, and syncytial. Therefore, the theory assumes that bilateral symmetry is more primitive than radial symmetry. However, current biological evidence shows that the most primitive forms of metazoans show radial symmetry, and thus radially symmetrical animals like cnidaria cannot be derived from bilateral flatworms. [15]

By concluding that the first multicellular animals were flatworms, it is also suggested that simpler organisms as sponges, ctenophores and cnidarians would have derived from  more complex animals. [16] However, most current molecular research has shown that sponges are the most primitive metazoans. [17] [18]

Germ layers are formed simultaneously

The syncytial theory rejects the theory of germ layers. During the development of the turbellaria (Acoela), three regions are formed without the formation of germ layers. From this, it was concluded that the germ layers are simultaneously formed during the cellularization process. This is in contrast to germ layer theory in which ectoderm, endoderm and mesoderm (in more complex animals) build up the embryo. [19]

The macro and micronucleus of Ciliates

There is a lot of evidence against ciliates being the metazoan ancestor.  Ciliates have two types of nuclei: a micronucleus which is used as germline nucleus and a macronucleus which regulates the vegetative growth. [20] This division of nuclei is a unique feature of the ciliates and is not found in any other members of the animal kingdom. [21] Therefore, it would be unlikely that ciliates are indeed the ancestors of the metazoans. This is confirmed by molecular phylogenetic research. Ciliates were never found close to animals in any molecular phylogeny. [22]

Flagellated sperm

Furthermore, the syncytial theory cannot explain the flagellated sperm of metazoans. Since the ciliate ancestor does not have any flagella and it is unlikely that the flagella arose as a de novo trait in metazoans,  the syncytial theory makes it almost impossible to explain the origin of flagellated sperm. [19]

Due to both the lack of molecular and morphological evidence for this theory, the alternative colonial theory of Haeckel, is currently gaining widespread acceptance.

For more theories see main article Multicellular organisms.

Cellularization in a syncytium (syncytium cellularization)

The development of cells in a syncytium (multinucleate cells) is termed syncytium cellularization. Syncytia are quite frequent in animals and plants. Syncytium cellularization occurs for instance in the embryonic development of animals and in endosperm development of plants. Here two examples:

Drosophila melanogaster development

In the embryonic development of Drosophila melanogaster , first 13 nuclear divisions take place forming a syncytial blastoderm consisting of approximately 6000 nuclei. During the later gastrulation stage, membranes are formed between the nuclei, and cellularization is completed. [23]

Syncytium cellularization in plants

The term syncytium cellularization is used for instance for a process of cell development in the endosperm of the Poaceae , e.g. barley (Hordeum vulgare), [24] rice (Oryza sativa). [25]

See also

Related Research Articles

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<span class="mw-page-title-main">Slime mold</span> Several unrelated spore-forming species

Slime mold or slime mould is an informal name given to several kinds of unrelated eukaryotic organisms with a life cycle that includes a free-living single-celled stage and the formation of spores. Spores are often produced in macroscopic multicellular or multinucleate fruiting bodies which may be formed through aggregation or fusion. Slime molds were formerly classified as fungi but are no longer considered part of that kingdom. Although not forming a single monophyletic clade, they are grouped within the paraphyletic group Protista.

Zoology is the scientific study of animals. Its studies include the structure, embryology, classification, habits, and distribution of all animals, both living and extinct, and how they interact with their ecosystems. Zoology is one of the primary branches of biology. The term is derived from Ancient Greek ζῷον, zōion ('animal'), and λόγος, logos.

<span class="mw-page-title-main">Multicellular organism</span> Organism that consists of more than one cell

A multicellular organism is an organism that consists of more than one cell, in contrast to unicellular organism. All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially uni- and partially multicellular, like slime molds and social amoebae such as the genus Dictyostelium.

A coenocyte is a multinucleate cell which can result from multiple nuclear divisions without their accompanying cytokinesis, in contrast to a syncytium, which results from cellular aggregation followed by dissolution of the cell membranes inside the mass. The word syncytium in animal embryology is used to refer to the coenocytic blastoderm of invertebrates. A coenocytic colony is referred to as a coenobium, and most coenobia are composed of a distinct number of cells, often as a multiple of two.

A syncytium or symplasm is a multinucleate cell which can result from multiple cell fusions of uninuclear cells, in contrast to a coenocyte, which can result from multiple nuclear divisions without accompanying cytokinesis. The muscle cell that makes up animal skeletal muscle is a classic example of a syncytium cell. The term may also refer to cells interconnected by specialized membranes with gap junctions, as seen in the heart muscle cells and certain smooth muscle cells, which are synchronized electrically in an action potential.

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Stuart Alan Newman is a professor of cell biology and anatomy at New York Medical College in Valhalla, NY, United States. His research centers around three program areas: cellular and molecular mechanisms of vertebrate limb development, physical mechanisms of morphogenesis, and mechanisms of morphological evolution. He also writes about social and cultural aspects of biological research and technology.

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<span class="mw-page-title-main">Holozoa</span> Clade containing animals and some protists

Holozoa is a clade of organisms that includes animals and their closest single-celled relatives, but excludes fungi and all other organisms. Together they amount to more than 1.5 million species of purely heterotrophic organisms, including around 300 unicellular species. It consists of various subgroups, namely Metazoa and the protists Choanoflagellata, Filasterea, Pluriformea and Ichthyosporea. Along with fungi and some other groups, Holozoa is part of the Opisthokonta, a supergroup of eukaryotes. Choanofila was previously used as the name for a group similar in composition to Holozoa, but its usage is discouraged now because it excludes animals and is therefore paraphyletic.

<span class="mw-page-title-main">Eukaryote</span> Domain of life whose cells have nuclei

The eukaryotes constitute the domain of Eukarya, organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms are eukaryotes. They constitute a major group of life forms alongside the two groups of prokaryotes: the Bacteria and the Archaea. Eukaryotes represent a small minority of the number of organisms, but due to their generally much larger size, their collective global biomass is much larger than that of prokaryotes.

<span class="mw-page-title-main">Outline of evolution</span>

The following outline is provided as an overview of and topical guide to evolution:

<span class="mw-page-title-main">Eukaryogenesis</span> Process of forming the first eukaryotic cell

Eukaryogenesis, the process which created the eukaryotic cell and lineage, is a milestone in the evolution of life, since eukaryotes include all complex cells and almost all multicellular organisms. The process is widely agreed to have involved symbiogenesis, in which archaea and bacteria came together to create the first eukaryotic common ancestor (FECA). This cell had a new level of complexity and capability, with a nucleus, at least one centriole and cilium, facultatively aerobic mitochondria, sex, a dormant cyst with a cell wall of chitin and/or cellulose and peroxisomes. It evolved into a population of single-celled organisms that included the last eukaryotic common ancestor (LECA), gaining capabilities along the way, though the sequence of the steps involved has been disputed, and may not have started with symbiogenesis. In turn, the LECA gave rise to the eukaryotes' crown group, containing the ancestors of animals, fungi, plants, and a diverse range of single-celled organisms.

<i>Sphaeroforma arctica</i> Species of protist

Sphaeroforma arctica, is a unicellular eukaryote with a pivotal position in the tree of life. It was first isolated from the arctic marine amphipod Gammarus setosus. Like other Ichthyosporeans such as Creolimax and Abeoforma, Sphaeroforma arctica are spherical cells characterized with their capacity to grow into multi-nucleated coenocytes. However, a unique feature of S. arctica, is that no obvious budding, hyphal, amoeboid, sporal or flagellated growth stages have been observed in laboratory growth conditions.

Oopsacas minuta is a glass sponge that is a member of the Hexactinellida. Oopsacas minuta is found in submarine caves in the Mediterranean. It is reproductive year-round. This species is a part of a class that are usually bathyal and abyssal. Meaning they grow at a depth over 200 meters. At this depth the temperature is low and constant, so silica metabolism is optimized. However, this species has been observed in shallow water. O. minuta have only been observed by exploring caves that trap cold water. The shape of the sponge is elongated, cylindrical and a little flared. It is between a few millimeters and 3.5 centimeters. O. minuta are white are held up with a siliceous skeleton. The spicules of the skeleton intersect in an intricate network. These spindles partially block the top of the sponge. There are no obvious oscules. The sponge is anchored or suspended from the cave by silica fibers. This class of sponge is different from the three other classes of Porifera. It differs in tissue organization, ecology, development and physiology. O. minuta belongs to the order Lyssacinosida. Lyssacinosida are characterized by the parenchymal spicules mostly being unconnected; this is unlike other sponges in the subclass where the spicules form a connected skeleton. The genome of O. minuta are one of the smallest of all the animal genomes that have been sequenced so far. Its genome contains 24 noncoding genes and 14 protein-encoding genes. The spindles of O. minuta have three axes and six points. This species does not have pinacocytes, which are the cells that form the outer layer in other sponges. Instead of true choanocytes it has frill structures that bud from the syncytium.

<i>Syssomonas</i> Genus of protists

Syssomonas is a monotypic genus of unicellular flagellated protists containing the species Syssomonas multiformis. It is a member of Pluriformea inside the lineage of Holozoa, a clade containing animals and their closest protistan relatives. It lives in freshwater habitats. It has a complex life cycle that includes unicellular amoeboid and flagellated phases, as well as multicellular aggregates, depending on the growth medium and nutritional state.

References

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  2. 1 2 3 4 5 Kandler, Otto (1995). "Cell Wall Biochemistry in Archaea and its Phylogenetic Implications". Journal of Biological Physics. 20 (1–4): 165–169. doi:10.1007/BF00700433. S2CID   83906865.
  3. 1 2 3 4 5 6 7 8 Kandler, Otto (1998). "The early diversification of life and the origin of the three domains: A proposal". In Jürgen Wiegel; Michael W.W. Adams (eds.). Thermophiles: The keys to molecular evolution and the origin of life?. London: Taylor and Francis Ltd. pp. 19–31. ISBN   978-0-203-48420-3.
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  5. ↑ Wächtershäuser, Günter (December 1988). "Before Enzymes and Templates: Theory of Surface Metabolism" (PDF). Microbiology and Molecular Biology Reviews. 52 (4): 452–484. doi:10.1128/mr.52.4.452-484.1988. PMC   373159 . PMID   3070320.
  6. ↑ Wächtershäuser, Günter (1998). "The Case for a Hyperthermophilic, Chemolithoautotrophic Origin of Life in an Iron-Sulfur World". In Jürgen Wiegel; Michael W.W. Adams (eds.). Thermophiles: The keys to molecular evolution and the origin of life?. London: Taylor and Francis Ltd. pp. 19–31. ISBN   978-0-203-48420-3.
  7. ↑ Woese, Carl R.; Kandler, Otto; Wheelis, M. L. (June 1990). "Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya". Proceedings of the National Academy of Sciences of the United States of America. 87 (12): 4576–4579. Bibcode:1990PNAS...87.4576W. doi: 10.1073/pnas.87.12.4576 . PMC   54159 . PMID   2112744.
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  10. ↑ Madigan, Michael T.; Martinko, John M.; Bender, Kelly S.; Buckley, Daniel H.; Stahl, David A. (2015). Brock Biology of Microorganisms (14 ed.). Boston: Pearson Education Limited. pp. 29, 374, 381. ISBN   978-1-292-01831-7.
  11. ↑ Madigan, Michael T.; Aiyer, Jennifer; Buckley, Daniel H.; Sattley, Matthew; Stahl, David A. (2022). Brock Biology of Microorganisms (16 ed.). Harlow: Pearson Education. pp. 431, 435. ISBN   978-1-292-40479-0.
  12. ↑ Schleifer, Karl-Heinz; Kandler, Otto (1972). "Peptidoglycan types of bacterial cell Walls and their taxonomic implications". Bacteriological Reviews. 36 (4): 407–775. doi:10.1128/br.36.4.407-477.1972. PMC   408328 . PMID   4568761.
  13. ↑ Hanson, Earl D. (1977). The origin and early evolution of animals (1st ed.). Middletown, Conn.: Wesleyan University Press. ISBN   0819550086. OCLC   2597099.
  14. ↑ Klautau, M.; Russo, C.A.M. (2016), "Metazoans, Origins of", Encyclopedia of Evolutionary Biology, Elsevier, pp. 1–6, doi:10.1016/b978-0-12-800049-6.00270-5, ISBN   9780128004265
  15. ↑ Pilato, Giovanni (2007). The origin and phylogeny of the metazoans and the theory of endoderm as secondary layer. Foxwell & Davies. ISBN   978-1905868063. OCLC   488084010.
  16. ↑ Waggoner, Ben (2001-04-25), "Eukaryotes and Multicells: Origin", eLS, John Wiley & Sons, Ltd, doi:10.1038/npg.els.0001640, ISBN   0470016175
  17. ↑ Schütze, Joachim; Krasko, Anatoli; Custodio, Marcio Reis; Efremova, Sofla M.; Müller, Isabel M.; Müller, Werner E. G. (1999-01-07). "Evolutionary relationships of Metazoa within the eukaryotes based on molecular data from Porifera". Proceedings of the Royal Society of London. Series B: Biological Sciences. 266 (1414): 63–73. doi:10.1098/rspb.1999.0605. ISSN   0962-8452. PMC   1689648 . PMID   10081159.
  18. ↑ Manuel, Michaël; Wörheide, Gert; Morgenstern, Burkhard; Erpenbeck, Dirk; Schreiber, Fabian; Jackson, Daniel J.; Leys, Sally; Guyader, Hervé Le; Wincker, Patrick (2009-04-28). "Phylogenomics Revives Traditional Views on Deep Animal Relationships". Current Biology. 19 (8): 706–712. doi: 10.1016/j.cub.2009.02.052 . ISSN   0960-9822. PMID   19345102.
  19. 1 2 R.L.Kotpal, Prof (2012). Modern Text Book of Zoology: Invertebrates. Rastogi Publications. ISBN   9788171339037.
  20. ↑ Prescott, D M (June 1994). "The DNA of ciliated protozoa". Microbiological Reviews. 58 (2): 233–267. doi:10.1128/MMBR.58.2.233-267.1994. ISSN   0146-0749. PMC   372963 . PMID   8078435.
  21. ↑ Lipscomb, Diana (March 1991). "Protoctists Close at Hand Handbook of Protoctista L. Margulis J. O. Corliss M. Melkonian D. J. Chapman". BioScience. 41 (3): 169–170. doi: 10.2307/1311459 . ISSN   0006-3568. JSTOR   1311459.
  22. ↑ Schlegel, Martin (September 1994). "Molecular phylogeny of eukaryotes". Trends in Ecology & Evolution. 9 (9): 330–335. doi:10.1016/0169-5347(94)90153-8. ISSN   0169-5347. PMID   21236876.
  23. ↑ Campos-Ortega, Jose A.; Hartenstein, Volker (2013-11-11). The Embryonic Development of Drosophila melanogaster. Springer Science & Business Media. ISBN   9783662224892.
  24. ↑ Journal Article The Dynamics of Transcript Abundance during Cellularization of Developing Barley Endosperm Runxuan Zhang, Matthew R. Tucker, Rachel A Burton, Neil J. Shirley, Alan Little, Jenny Morris, Linda Milne, Kelly Houston, Pete E. Hedley, Robbie Waugh, Geoffrey B. Fincher (2016). "The Dynamics of Transcript Abundance during Cellularization of Developing Barley Endosperm". Plant Physiology. 170 (3): 1549–1565. doi:10.1104/pp.15.01690.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  25. ↑ Masanori Mizutani, Takuma Naganuma, Ken-ichi Tsutsumi, Yasushi Saitoh (2010). "The syncytium-specific expression of the Orysa;KRP3 CDK inhibitor: implication of its involvement in the cell cycle control in the rice (Oryza sativa L.) syncytial endosperm". Journal of Experimental Botany. 61 (3): 791–798. doi:10.1093/jxb/erp343. PMC   2814109 . PMID   19933315.{{cite journal}}: CS1 maint: multiple names: authors list (link)
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