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Author Topic: How do cells migrate in a developing embryo?  (Read 2089 times)

Offline thedoc

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How do cells migrate in a developing embryo?
« on: 29/07/2013 03:30:01 »
Dalton  asked the Naked Scientists:
   
Back when I was in school, I recollect being told that cell and tissue specialisation was controlled by gradients of hormones.

Nowadays, there's a lot of talk about cell signaling, quorum sensing, cascading genetic events, and migratory behavior over scaffoldings. I'm having problems envisioning how non-motile cells can migrate from one part of the brain to another. Since there are no flagella or cilia (that I'm aware of) any migratory behavior would have to occur by either an amoeboid mechanism or undulating membrane up a chemotaxic gradient. Perhaps you can clear this up for me.

Sincerely,
Dalton Seymour - USA

What do you think?
« Last Edit: 29/07/2013 03:30:01 by _system »


 

Offline Lmnre

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Re: How do cells migrate in a developing embryo?
« Reply #1 on: 29/07/2013 02:21:35 »
Yes, migratory behavior of certain brain neurons can and does occur by means of an amoeboid mechanism.

In the brain, the layers of the cerebral cortex originate deep within the brain near the liquid-filled ventricles and migrate outward using an amoeboid mechanism (that is, using pseudopodia) through the existing brain up a chemotaxic gradient emanating from the brain's surface, where they install themselves.

The cerebral cortex consists of several layers of cortical neurons. Each layer consists of about one billion neurons, making the cerebral cortex about six to eight billion neurons. These are the cells that make us human — they allow us to sense, process and remember abstract information. Each layer has its own migration period and its own chemotaxic gradient. The migration periods are fixed, so that when the brain stops producing the chemotaxic gradient, the migrating neurons stop and install themselves wherever they are — presumably at the brain's surface.

The migration is somewhat like the children's game Grandmother's Footsteps (in the UK) or Red Light, Green Light (in the US). When the person who is "it" turns around, the players stop where they are. In the brain, the migrating neurons should have reached the surface of the brain when the the brain stops producing the gradient. However, any amount of alcohol present slows down the neurons' movement, or confuses the neurons, or dulls their sensitivity to the gradient¹; and when the brain stops producing the gradient, some or all of the migrating neurons may not have reached the surface of the brain.

So, alcohol literally scrambles the brain's cerebral cortex and denies the neurons their proper communications with each other and the rest of the brain, making the individual less human and less able to deal with the abstract. This is why alcohol is called a teratogen — literally, a "monster-maker". Abstract information doesn't exist only at the top end of human knowledge (such as calculus or philosophy). There are extremely important amounts of abstract information in everyday life — telling time, doing simple math, having a "moral compass", having a sense of humor², perceiving other people's feelings and motives, etc.

I knew of a man affected by his mother's alcoholism while pregnant with him who graduated high school, drove a car with a manual transmission, worked as a technician, married and had children. So, he seemed fairly able and successful, right? However, he couldn't tell time until middle school, didn't learn all his basic arithmetic before graduation (academically his HS diploma was useless), was a pedophile, thought all jokes were about him, and so seriously failed at perceiving other people's feelings and motives that he was considered a psychopath.

This is what can and does result from pregnant women who drink. So, as far as I'm concerned, people who claim that "one drink a day is okay" are promoting abusing babies in a horrifically insidious manner, who thereafter never live a normal life — not even for one second — and they endanger people who become involved with them. The inability of people to talk honestly and openly about this taboo topic is the reason why alcohol is STILL the leading cause of birth defects in the developed world. Although 100% permanent, it is also, shamefully, 100% preventable.

I hope my pointed narration hasn't strayed too far from the answer to your question, which is that migratory behavior of certain brain neurons can and does occur by means of an amoeboid mechanism.

¹ The precise mechanism was unclear to researchers when I studied this topic 20 years ago.
² If you don't think abstract information exists in humor, have you ever seen a chicken cross the road, or have you ever seen a priest, a minister and a rabbi walk into a bar? Almost everyone must imagine such situations.
« Last Edit: 29/07/2013 02:23:17 by Lmnre »
 

Offline Dalton

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Re: How do cells migrate in a developing embryo?
« Reply #2 on: 30/07/2013 04:54:59 »
Thanks Lmnre for replying. However, it prompts a couple more questions concerning the embryological development. 1) When they refer to the chemotaxic gradient, is it the same chemical attractant for all developing neurons or is there a specific type chemical gradient related to a limited number of evolving neuron types?  I'm assuming here that the migrating cells are still immature and to some degree stem cell like. 2) When reference is made to the scaffolding they migrate over, what is the nature of that scaffolding? I recollect reference being made to scaffolding employed in growing artificial organs as being non-cellular substances which eventually break down and are reabsorbed? I ask this question because I have seen the statement that neurogenesis by the hippocampus involves the eventual migration of new neurons to some target region, so this would imply that the scaffolding continues to exist or is reconstructed as part of the neurogenesis process. Is this true for the structure of the brain as well? Also, what is the origin of the scaffolding?

Sincerely,
Dalton Seymour
 

Offline Lmnre

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Re: How do cells migrate in a developing embryo?
« Reply #3 on: 30/07/2013 17:40:40 »
1. It's a specific type of chemical gradient for each migration group, at least concerning the development of the cerebral cortex. The migrating cells aren't in their ultimate stage, because of the amoeboid movement they require and because their ultimate stage forms connections with approximately 50,000 other neurons, and the two don't seem compatible (at least to me).

2. It's more like the scaffolding they must climb through, like a kid climbing out of a jungle gym. The scaffolding is the existing neurons in the cerebrum (I would say mostly white cells), and purely structural cells. such as glia cells, and when the migrating neurons reach the cortical regions, they climb through any previous layers of cortical cells that have gone before and installed themselves at the surface. I'm not familiar with the entire scaffolding structure of the brain, but I do know of the glia cells, and there may be other components, including those that are not cells.

On the origin of the scaffolding, there's at least the white brain cells and glia cells, where the glia cells are purely structural. What I remember of the white cells, they seem mostly to be interconnections of regions within the cerebrum (such as, between the various areas of the visual system), and with the rest of the body (such as the muscles and the senses). I'm not remembering much about the scaffolding, and I don't remember about its development.
 

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Re: How do cells migrate in a developing embryo?
« Reply #3 on: 30/07/2013 17:40:40 »

 

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