Advertisements

We're a little crazy, about science!

New discovery sheds light on the forming brain

Brain-waves

The cerebral cortex, which controls higher processes such as perception, thought and cognition, is the most complex structure in the mammalian central nervous system. Although much is known about the intricate structure of this brain region, the processes governing its formation remain uncertain. Research has now uncovered how feedback between cells, as well as molecular factors, helps shape cortical development during mouse embryogenesis.

The cortex is made up of layers of interconnecting cells that are produced in a particular order from progenitor cells. The relatively cell-sparse outer layer is formed first, then the dense deep layer, and finally the tightly packed upper layer.

The team was interested to discover exactly how the various layers form, so they created a mouse model that enabled them to control the expression of a particular protein, Foxg1, known to be involved in cortical development.

The Foxg1 gene, if switched on toward the end of embryogenesis after the outer layer of neurons has formed, triggers the production of deep-layer neurons, followed by upper-layer neurons. The researchers found that it does this by repressing the activity of another gene, called Tbr1, in the outer-layer neurons.

Genetics, however, is not the only factor that influences the development of this complicated laminar structure. In a separate experiment, the researchers let natural embryonic development run its course until the deep-layer neurons had formed, after which they selectively killed off these cells. At a point in time when the production of deep-layer cells would normally have ceased, it instead continued.

Fluorescence microscopy image of a mouse cortex during brain development. Blue cells are deep-layer neurons, green cells are Foxg1 active cells and red cells are upper-layer neurons. This image shows that the onset of Foxg1 activity instructs the production of both deep- and upper-layer neurons. Photo credit goes to: K. Toma et al. Reproduced from  "Ref. 1"

Fluorescence microscopy image of a mouse cortex during brain development. Blue cells are deep-layer neurons, green cells are Foxg1 active cells and red cells are upper-layer neurons. This image shows that the onset of Foxg1 activity instructs the production of both deep- and upper-layer neurons.
Photo credit goes to: K. Toma et al. Reproduced from
“Ref. 1”

The absence of the ‘production stop’ signal from deep-layer neurons caused the progenitor cells to continue to make deep-layer neurons.

“Before this study, there was no evidence for any feedback between post-mitotic neurons and progenitors,” says Carina Hanashima from the RIKEN Center for Developmental Biology, “but we’ve shown that the two cell types do communicate.”

Extrinsic, cellular factors as well as intrinsic, genetic cues help to guide cortical development. This mechanism allows the developing brain to balance the various different cell types found in the neocortex: it gives the brain flexibility to adjust if too few of one cell type are produced.

Although the numbers of cells and embryonic and gestational periods differ significantly between mice and humans, both species are endowed with almost identical genetic toolkits, and consequently the researchers think it is likely that the human neocortex is generated in much the same way.

Sources
Toma K. & C. Hanashima (2014). The Timing of Upper-Layer Neurogenesis Is Conferred by Sequential Derepression and Negative Feedback from Deep-Layer Neurons, Journal of Neuroscience, 34 (39) 13259-13276. DOI: http://dx.doi.org/10.1523/jneurosci.2334-14.2014

Advertisements

2 responses

  1. Jordan

    I think this is very interesting. I have always found the development of the brain and learning about the different parts of the brain to be intriguing. This article mentions the cerebral cortex being the most complex structure in the central nervous system of mammals. This is exactly what I have been reading about in class. The organization of the cerebral cortex is very complex and contains six distinct laminae. These laminae have control over various parts of our body. For example, Laminae V, sends long axons to the spinal cord and has the greatest control of muscles.

    February 13, 2015 at 11:40 am

    • Awesome, I’m glad you liked the article and that it fit into your studies!

      February 13, 2015 at 12:45 pm

But enough about us, what about you?

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s