Oh Yeah, Developmental Biology!

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Posts tagged with "morphogenesis"

Feb 7

laura-mariesaul:

Organic 2 by AMagill on Flickr.

Morphogenesis & Pattern Formation

Mathematical biology and Morphogenesis was the last work in which Turing worked on. He wanted to decode the markings and patterns formed in nature such as patterns on animals or patterns formed in plant structures and how they emerge. His reaction-diffusion model was the basis to understanding pattern formation.

Defining the terms.

Morphogenesis is concerned with the shapes of tissues, organs and entire organisms and the positions of the various specialized cell types. The evolutionary development of form in an organism.

Pattern formation is the creation of a predictable arrangement of cell types in space during embryonic development. The types of patterns of cell types found in animals and plants can be conveniently described as simple or complex. Pattern formation is one of four processes that underlie development, the others being growth, cell diversification, and morphogenesis.

The video above shows an experiment to show Alan Turing’s Reaction-Diffusion algorithm for morphogenesis. The video itself is quite hyponotic and reminds me of Op Art in the 60s, artists such as Bridget Riley, who used monochrome patterns to create optical illusions. Pattern formation could be a good angle to work with due to the abstract approach this could take me.

http://www.thefreedictionary.com/morphogenesis

http://www.sciencedaily.com/articles/m/morphogenesis.htm

http://encyclopedia2.thefreedictionary.com/pattern+formation

This was what my dissertation was about. 

May 3
In the 1960s Lewis Wolpert devised a model to describe basic pattern formation in development. This model was known as the French Flag Model. It is a useful model as the formation of the three colours of the flag can be used to understand the formation of the three germ layers present in embryos. The first thing to note is that no matter what size the flag, it still maintains the same basic pattern. One third will be blue, one third white and one third red, in that order, along one axis. Second, in a line of cells with defined boundaries, each cell has the potential to differentiate into a blue, white or red cell. Wolpert set out to try and explain the mechanism behind how the cells know which colour they should differentiate into. Cells must receive some form of information to deduce where they are situated within the flag model, and then according to their genetic program interpret this information by differentiating into one of the three cell types. 
There are two stages of pattern formation, first the cells have to establish their position and then they have to interpret this information. The fact that a clear distinction has been made between these two processes implies that there is no set relation between a cells position and the how it interprets the information it is sent. Thus in a different set of parameters these cells are capable of producing a completely different pattern. Wolpert devised a simple way to explain how a cell establishes its orientation, based on the gradient of a substance. If the concentration of a chemical substance decreases from one end of the flag to the other a cell could work out where exactly it was positioned in relation to the boundaries. This would be due to the amount of chemical substance the cell received. This Chemical substance is known as a Morphogen. Morphogens are described as substances in embryonic tissues that form a concentration gradient and influences morphogenesis.
In the French Flag Model we assume the concentration is greatest at one end and lowest at the opposite end and so the morphogen diffuses at a constant rate down the line of cells. It is also safe to assume that the cells respond to threshold concentrations of the morphogen. Above a particular concentration threshold blue cells will form, whilst below this concentration threshold but above another, white cells will form. Below both these concentration thresholds red cells form creating the complete French Flag pattern.

The threshold could be one of two things; the specific amount of morphogen need to bind to receptors on the cells in order to activate intracellular signalling cascades, or differing concentrations of transcription factors, which are required to activate certain genes within the cells. 
This model highlights two important features of morphogenesis. Firstly, even if the length of the line of cells varies, patterns will still from in the correct proportions, as long as defined boundaries are present with constant but differing concentrations of morphogen at either end. Secondly the pattern could regenerate itself to the complete original form after being cut in half, as long as the defined boundaries and concentrations were re-established. 
[Adapted from Wolpert Principles of developmental Biology]

In the 1960s Lewis Wolpert devised a model to describe basic pattern formation in development. This model was known as the French Flag Model. It is a useful model as the formation of the three colours of the flag can be used to understand the formation of the three germ layers present in embryos. The first thing to note is that no matter what size the flag, it still maintains the same basic pattern. One third will be blue, one third white and one third red, in that order, along one axis. Second, in a line of cells with defined boundaries, each cell has the potential to differentiate into a blue, white or red cell. Wolpert set out to try and explain the mechanism behind how the cells know which colour they should differentiate into. Cells must receive some form of information to deduce where they are situated within the flag model, and then according to their genetic program interpret this information by differentiating into one of the three cell types.

There are two stages of pattern formation, first the cells have to establish their position and then they have to interpret this information. The fact that a clear distinction has been made between these two processes implies that there is no set relation between a cells position and the how it interprets the information it is sent. Thus in a different set of parameters these cells are capable of producing a completely different pattern. Wolpert devised a simple way to explain how a cell establishes its orientation, based on the gradient of a substance. If the concentration of a chemical substance decreases from one end of the flag to the other a cell could work out where exactly it was positioned in relation to the boundaries. This would be due to the amount of chemical substance the cell received. This Chemical substance is known as a Morphogen. Morphogens are described as substances in embryonic tissues that form a concentration gradient and influences morphogenesis.

In the French Flag Model we assume the concentration is greatest at one end and lowest at the opposite end and so the morphogen diffuses at a constant rate down the line of cells. It is also safe to assume that the cells respond to threshold concentrations of the morphogen. Above a particular concentration threshold blue cells will form, whilst below this concentration threshold but above another, white cells will form. Below both these concentration thresholds red cells form creating the complete French Flag pattern.

The threshold could be one of two things; the specific amount of morphogen need to bind to receptors on the cells in order to activate intracellular signalling cascades, or differing concentrations of transcription factors, which are required to activate certain genes within the cells.

This model highlights two important features of morphogenesis. Firstly, even if the length of the line of cells varies, patterns will still from in the correct proportions, as long as defined boundaries are present with constant but differing concentrations of morphogen at either end. Secondly the pattern could regenerate itself to the complete original form after being cut in half, as long as the defined boundaries and concentrations were re-established. 

[Adapted from Wolpert Principles of developmental Biology]



The development of an animal from an egg has been a source of wonder throughout history

- Gilbert, developmental biology page 4 

Alan Turing’s Patterns in Nature, and Beyond

Near the end of his life, the great mathematician Alan Turing wrote his first and last paper on biology and chemistry, about how a certain type of chemical reaction ought to produce many patterns seen in nature.

Called “The Chemical Basis of Morphogenesis,” it was an entirely theoretical work. But in following decades, long after Turing tragically took his own life in 1954, scientists found his speculations to be reality.

First found in chemicals in dishes, then in the stripes and spirals and whorls of animals, so-called Turing patterns abounded. Some think that Turing patterns may actually extend to ecosystems, even to galaxies. That’s still speculation — but a proof published Feb. 11 in Science of Turing patterns in a controlled three-dimensional chemical system are even more suggestion of just how complex the patterns can be.

On the following pages, Wired.com takes you on a Turing pattern tour.

This is what im currently doing my dissertation on. Click through to see the amazing work of Alan Turing.