New way for cell differentiation: Reaction, diffusion and chaotic waves

A cellular automaton model, Morphozoic, is presented. Morphozoic may be used to investigate the computational power of morphogenetic fields to foster the development of structures and cell differentiation. The term morphogenetic field is used here to describe a generalized abstraction: a cell signals information about its state to its environment and is able to sense and act on signals from nested neighborhood of cells that can represent local to global morphogenetic effects. Neighborhood signals are compacted into aggregated quantities, capping the amount of information exchanged: signals from smaller, more local neighborhoods are thus more finely discriminated, while those from larger, more global neighborhoods are less so. An assembly of cells can thus cooperate to generate spatial and temporal structure. Morphozoic was found to be robust and noise tolerant. Applications of Morphozoic presented here include: 1) Conway's Game of Life, 2) Cell regeneration, 3) Evolution of a gastrulation-like sequence, 4) Neuron pathfinding, and 5) Turing's reaction-diffusion morphogenesis.

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HetL, HetR and PatS form a reaction-diffusion system to control pattern formation in the cyanobacterium nostoc PCC 7120

eLife ◽

10.7554/elife.59190 ◽

2020 ◽

Vol 9 ◽

Cited By ~ 1

Author(s):

Xiaomei Xu ◽

Véronique Risoul ◽

Deborah Byrne ◽

Stéphanie Champ ◽

Badreddine Douzi ◽

...

Keyword(s):

Cell Differentiation ◽

Pattern Formation ◽

Long Range ◽

Nitrogen Starvation ◽

Reaction Diffusion ◽

Protective Mechanism ◽

Control Pattern ◽

Differentiation Pattern ◽

Biological Patterns ◽

Pcc 7120

Local activation and long-range inhibition are mechanisms conserved in self-organizing systems leading to biological patterns. A number of them involve the production by the developing cell of an inhibitory morphogen, but how this cell becomes immune to self-inhibition is rather unknown. Under combined nitrogen starvation, the multicellular cyanobacterium Nostoc PCC 7120 develops nitrogen-fixing heterocysts with a pattern of one heterocyst every 10–12 vegetative cells. Cell differentiation is regulated by HetR which activates the synthesis of its own inhibitory morphogens, diffusion of which establishes the differentiation pattern. Here, we show that HetR interacts with HetL at the same interface as PatS, and that this interaction is necessary to suppress inhibition and to differentiate heterocysts. hetL expression is induced under nitrogen-starvation and is activated by HetR, suggesting that HetL provides immunity to the heterocyst. This protective mechanism might be conserved in other differentiating cyanobacteria as HetL homologues are spread across the phylum.

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Singular limit of reaction–diffusion systems and modified motion by mean curvature

Proceedings of the Royal Society of Edinburgh Section A Mathematics ◽

10.1017/s030821050200046x ◽

2002 ◽

Vol 132 (04) ◽

pp. 951

Keyword(s):

Mean Curvature ◽

Reaction Diffusion ◽

Singular Limit ◽

Reaction Diffusion Systems ◽

Diffusion Systems ◽

Motion By Mean Curvature

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Surface reactions observed by photoemission electron microscopy (PEEM)

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100121831 ◽

1992 ◽

Vol 50 (1) ◽

pp. 286-287

Author(s):

H.H. Rotermund

Keyword(s):

Electron Microscopy ◽

Electron Microscope ◽

Work Function ◽

Chemical Reactions ◽

Reaction Diffusion ◽

Dynamic Processes ◽

Clean Surface ◽

Crystal Surfaces ◽

Single Crystal Surfaces ◽

Photoemission Electron

Chemical reactions at a surface will in most cases show a measurable influence on the work function of the clean surface. This change of the work function δφ can be used to image the local distributions of the investigated reaction,.if one of the reacting partners is adsorbed at the surface in form of islands of sufficient size (Δ>0.2μm). These can than be visualized via a photoemission electron microscope (PEEM). Changes of φ as low as 2 meV give already a change in the total intensity of a PEEM picture. To achieve reasonable contrast for an image several 10 meV of δφ are needed. Dynamic processes as surface diffusion of CO or O on single crystal surfaces as well as reaction / diffusion fronts have been observed in real time and space.

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Electron microscope study of the secretory activity of epithelial cells in embryonic thymus

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010015945x ◽

1990 ◽

Vol 48 (3) ◽

pp. 382-383

Author(s):

H. Alasam

Keyword(s):

Cell Differentiation ◽

T Cell ◽

Epithelial Cells ◽

Electron Density ◽

Secretory Activity ◽

T Cell Differentiation ◽

High Electron ◽

Transmission Electron ◽

Medullary Epithelial Cells ◽

Thymic Factor

The possibility that intrathymic T-cell differentiation involves stem cell-lymphoid interactions in embryos led us to study the ultrastructure of epithelial cell in normal embryonic thymus. Studies in adult thymus showed that it produces several peptides that induce T-cell differentiation. Several of them have been chemically characterized, such as thymosin α 1, thymopoietin, thymic humoral factor or the serum thymic factor. It was suggested that most of these factors are secreted by populations of A and B-epithelial cells.Embryonic materials were obtained from inbred matings of Swiss Albino mice. Thymuses were disected from embryos 17 days old and prepared for transmission electron microscopy. Our studies showed that embryonic thymus at this stage contains undifferentiated and differentiated epithelial cells, large lymphoblasts, medium and few small lymphocytes (Fig. 5). No differences were found between cortical and medullary epithelial cells, in contrast to the findings of Van Vliet et al,. Epithelial cells were mostly of the A-type with low electron density in both cytoplasm and nucleus. However few B-type with high electron density were also found (Fig. 7).

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