Morphogenesis

Source: Wikipedia, the free encyclopedia.
This article is about the biological process. For other uses, see Morphogenesis (disambiguation).

Morphogenesis (from the Greek morphê shape and genesis creation, literally "the generation of form") is the biological process that causes a cell, tissue or organism to develop its shape. It is one of three fundamental aspects of developmental biology along with the control of tissue growth and patterning of cellular differentiation.

The process controls the organized spatial distribution of cells during the

unicellular life forms that do not have an embryonic stage in their life cycle. Morphogenesis is essential for the evolution
of new forms.

Morphogenesis is a mechanical process involving forces that generate mechanical stress, strain, and movement of cells,

dysmorphogenesis
.

History

Further information: Evolutionary developmental biology § History, and Turing pattern

Some of the earliest ideas and mathematical descriptions on how physical processes and constraints affect biological growth, and hence

spirals of phyllotaxis, were written by D'Arcy Wentworth Thompson in his 1917 book On Growth and Form[2][3][note 1] and Alan Turing in his The Chemical Basis of Morphogenesis (1952).[6] Where Thompson explained animal body shapes as being created by varying rates of growth in different directions, for instance to create the spiral shell of a snail, Turing correctly predicted a mechanism of morphogenesis, the diffusion of two different chemical signals, one activating and one deactivating growth, to set up patterns of development, decades before the formation of such patterns was observed.[7] The fuller understanding of the mechanisms involved in actual organisms required the discovery of the structure of DNA in 1953, and the development of molecular biology and biochemistry.[citation needed
]

Genetic and molecular basis

bicoid
, setting up stripes which create the body's segmental form.
Further information: evolutionary developmental biology, transcription factor, and gene regulatory network

Several types of molecules are important in morphogenesis.

transcription of other genes; in turn, these secondary gene products can regulate the expression of still other genes in a regulatory cascade of gene regulatory networks. At the end of this cascade are classes of molecules that control cellular behaviors such as cell migration, or, more generally, their properties, such as cell adhesion or cell contractility. For example, during gastrulation, clumps of stem cells switch off their cell-to-cell adhesion, become migratory, and take up new positions within an embryo where they again activate specific cell adhesion proteins and form new tissues and organs. Developmental signaling pathways implicated in morphogenesis include Wnt, Hedgehog, and ephrins.[8]

Cellular basis

E-cadherin
than the green cells. The mixed culture forms large multi-cellular aggregates.

At a tissue level, ignoring the means of control, morphogenesis arises because of cellular proliferation and motility.[9] Morphogenesis also involves changes in the cellular structure[10] or how cells interact in tissues. These changes can result in tissue elongation, thinning, folding, invasion or separation of one tissue into distinct layers. The latter case is often referred as cell sorting. Cell "sorting out" consists of cells moving so as to sort into clusters that maximize contact between cells of the same type. The ability of cells to do this has been proposed to arise from differential cell adhesion by Malcolm Steinberg through his differential adhesion hypothesis. Tissue separation can also occur via more dramatic cellular differentiation events during which epithelial cells become mesenchymal (see Epithelial–mesenchymal transition). Mesenchymal cells typically leave the epithelial tissue as a consequence of changes in cell adhesive and contractile properties. Following epithelial-mesenchymal transition, cells can migrate away from an epithelium and then associate with other similar cells in a new location.[11] In plants, cellular morphogenesis is tightly linked to the chemical composition and the mechanical properties of the cell wall.[12][13]

Cell-to-cell adhesion

During embryonic development, cells are restricted to different layers due to differential affinities. One of the ways this can occur is when cells share the same cell-to-

E-cadherin (found on many epithelial cells) binds preferentially to other E-cadherin molecules. Mesenchymal cells usually express other cadherin types such as N-cadherin.[14][15]

Extracellular matrix

The

α-actinin and talin to link the cytoskeleton with the outside. Integrins also serve as receptors to trigger signal transduction cascades when binding to the ECM. A well-studied example of morphogenesis that involves ECM is mammary gland ductal branching.[16][17]

Cell contractility

Tissues can change their shape and separate into distinct layers via cell contractility. Just as in muscle cells, myosin can contract different parts of the cytoplasm to change its shape or structure. Myosin-driven contractility in embryonic tissue morphogenesis is seen during the separation of germ layers in the model organisms Caenorhabditis elegans, Drosophila and zebrafish. There are often periodic pulses of contraction in embryonic morphogenesis. A model called the cell state splitter involves alternating cell contraction and expansion, initiated by a bistable organelle at the apical end of each cell. The organelle consists of microtubules and microfilaments in mechanical opposition. It responds to local mechanical perturbations caused by morphogenetic movements. These then trigger traveling embryonic differentiation waves of contraction or expansion over presumptive tissues that determine cell type and is followed by cell differentiation. The cell state splitter was first proposed to explain neural plate morphogenesis during gastrulation of the axolotl[18] and the model was later generalized to all of morphogenesis.[19][20]

Branching morphogenesis

Further information: Lung § Development, and Breast development

In the development of the

respiratory tree.[21] The branching is a result of the tip of each bronchiolar tube bifurcating, and the process of branching morphogenesis forms the bronchi, bronchioles, and ultimately the alveoli.[22]

Branching morphogenesis is also evident in the

ductal formation of the mammary gland.[23][17] Primitive duct formation begins in development, but the branching formation of the duct system begins later in response to estrogen during puberty and is further refined in line with mammary gland development.[17][24][25]

Cancer morphogenesis

Cancer can result from disruption of normal morphogenesis, including both tumor formation and tumor metastasis.[26] Mitochondrial dysfunction can result in increased cancer risk due to disturbed morphogen signaling.[26]

Virus morphogenesis

During assembly of the bacteriophage (phage) T4 virion, the morphogenetic proteins encoded by the phage genes interact with each other in a characteristic sequence. Maintaining an appropriate balance in the amounts of each of these proteins produced during viral infection appears to be critical for normal phage T4 morphogenesis.[27] Phage T4 encoded proteins that determine virion structure include major structural components, minor structural components and non-structural proteins that catalyze specific steps in the morphogenesis sequence.[28] Phage T4 morphogenesis is divided into three independent pathways: the head, the tail and the long tail fibres as detailed by Yap and Rossman.[29]

Computer models

An approach to model morphogenesis in computer science or mathematics can be traced to Alan Turing's 1952 paper, "The chemical basis of morphogenesis",[30] a model now known as the Turing pattern.

Another famous model is the so-called French flag model, developed in the sixties.[31]

Improvements in computer performance in the twenty-first century enabled the simulation of relatively complex morphogenesis models. In 2020, such a model was proposed where cell growth and differentiation is that of a cellular automaton with parametrized rules. As the rules' parameters are differentiable, they can be trained with gradient descent, a technique which has been highly optimized in recent years due to its use in machine learning.[32] This model was limited to the generation of pictures, and is thus bi-dimensional.

A similar model to the one described above was subsequently extended to generate three-dimensional structures, and was demonstrated in the video game Minecraft, whose block-based nature made it particularly expedient for the simulation of 3D cellular automatons.[33]

See also

Notes

  1. ^ Thompson's book is often cited. An abridged version, comprising 349 pages, remains in print and readily obtainable.[4] An unabridged version, comprising 1116 pages, has also been published.[5]

References

  1. PMID 31365867
    .
  2. ^ Thompson, D'Arcy Wentworth (1917). On Growth and Form. Cambridge University Press.
  3. S2CID 27982230, archived from the original
    (PDF) on 28 November 2014, retrieved 11 December 2012
  4. ISBN 978-0-521-43776-9
    , retrieved 11 December 2012
  5. ISBN 978-0-486-67135-2
  6. doi:10.1098/rstb.1952.0012
    .
  7. PMID 26771020
    .
  8. PMID 17039550
    .
  9. PMID 27544910
    .
  10. PMID 33449631
    .
  11. ISBN 978-0-87893-243-6
    .
  12. PMID 26689854
    .
  13. PMID 29229695
    .
  14. PMID 18848899
    .
  15. PMID 11171368
    .
  16. PMID 14680479
    .
  17. ^
    PMID 16524451
    .
  18. S2CID 4349055
    .
  19. PMID 26965444
    .
  20. ISBN 978-981-4350-48-8
    .
  21. ISBN 978-0-19-967814-3
    .
  22. PMID 18023732
    .
  23. PMID 14680479
    .
  24. PMID 20554705
    .
  25. ISBN 978-1-4511-4870-1
    .
  26. ^
    S2CID 4538888. Archived from the original
    (PDF) on 2017-09-21.
  27. PMID 4907266
    .
  28. PMID 4878023
    .
  29. PMID 25517898
    .
  30. S2CID 937133
    .
  31. PMID 25804733
    .
  32. S2CID 213719058
    .
  33. arXiv:2103.08737 [cs.LG
    ].

Further reading

  • Bard, J. B. L. (1990). Morphogenesis: The Cellular and Molecular Processes of Developmental Anatomy. Cambridge, England: Cambridge University Press.
  • Slack, J. M. W. (2013). Essential Developmental Biology. Oxford: Wiley-Blackwell.

External links

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