Development

Secondary neurolation refers to the development of posterior anterior( posterior, anterior ) parts. Tubes from both primary and secondary neurulation eventually connect remain separated( eventually connect, remain separated ).

BMP4 signal induces epidermal neural( epidermal, neural ) differentiation.
Inhibition Expression( Inhibition, Expression ) of BMP is necessary to allow neural development.

These processes are combined with signalling from FGF G-proteins( FGF, G-proteins ).

Sonic hedgehog is secreted by the notochord ectoderm( notochord, ectoderm ) and the floor roof( floor, roof ) plate.

Differences in the concentration of sonic hedgehog (a single protein) can determine the fate of multiple neuronal classes in the ventral dorsal caudal rostral( ventral, dorsal, caudal, rostral ) part of the neural tube.

In a first step a ventral-to-dorsal Shh gradient activates and represses activates represses( activates and represses, activates, represses ) different transcription factors.
These repress enhance( repress, enhance ) each other's expression to confer cell identity to progenitor cells unambiguously.

Five cardinal progenitor domains are established:
Four types of interneurons sensory neurons( interneurons, sensory neurons ) (V0 - V3) and motor neurons sensory neurons( motor neurons, sensory neurons ).

The dorsal neural tube is patterned by BMP FGF Shh( BMP, FGF, Shh ) and dorsalin.

Overexpression of Gbx2 shifts the midbrain-hindbrain boundary anteriorly posteriorly( anteriorly, posteriorly ).

Cells form the zona limitans intrathalamica secrete Shh BMP Wnt FGF( Shh, BMP, Wnt, FGF ) which gives rise to the nuclei of the thalamus.

Neural progenitors Stem cells Neurons Glia cells( Neural progenitors, Stem cells, Neurons, Glia cells ) can divide symmetrically to two differentiated cells or two more progenitor cells.

Or they can divide asymmetrically to one differentiated cell and one progenitor cell.

Neurogenesis is the process by which a multitude of postmitotic premitotic( postmitotic, premitotic ) neurons are generated from relatitvely few a large number of( relatitvely few, a large number of ) neural stem cells / progenitors in the neural epithelium ectoderm endoderm( epithelium, ectoderm, endoderm ).

Neural stem cells are self-renewing and multipotent unipotent( multipotent, unipotent ).

Proneural genes give each cell in a group (proneural cluster group array( cluster, group, array )) the same a different( the same, a different ) competence to become a proneuroblast.

Lateral Forward( Lateral, Forward ) inhibition by delta-notch and a basic helix-loop-helix basic loop-helix-loop( basic helix-loop-helix, basic loop-helix-loop ) transcriptional cascade:

More Delta in one cell enhances reduces( enhances, reduces ) transcription of suppressor of hairless.
Suppressor of hairless increases decreases( increases, decreases ) transcription of enhancer of split.
Enhancer of split represses enhances( represses, enhances ) achaete-scute.
Achaete-scute would increases expression of Delta but now does not.
Therefore no Notch signalling in the original cell.

In the subventricular zone stem cell niche cells transcription factors basic helix-loop-helix cascades( stem cell niche cells, transcription factors, basic helix-loop-helix cascades ) regulate whether stem cells proliferate or divide asymmetrically symmetrically( asymmetrically, symmetrically ) (with one differentiating daughter cell) .

This mechanism is regulated by signals from the blood vessels transcription factors basic helix-loop-helix cascades( signals from the blood vessels, transcription factors, basic helix-loop-helix cascades ).

A good example for intracellular regulatory proteins that guide the growth of axons and can be both attracting and repelling are Netrins Semaphorins Ephrins Cadherins( Netrins, Semaphorins, Ephrins, Cadherins ).

They occur in particular at the floor plate roof plate( floor plate, roof plate ) of the neural tube and filopodia can have different receptors for them.

Gradients of Eph Ephrin Netrin Net( Eph, Ephrin, Netrin, Net ) receptors and Ephrin Eph Netrin Net( Ephrin, Eph, Netrin, Net ) ligands are responsible for the retinotopic organization of the tectum.

Their cues are inhibitory / repelling excitatory / attracting( inhibitory / repelling, excitatory / attracting ).

The Shh pathway:

Shh inhibits induces( inhibits, induces ) patched smoothened( patched, smoothened ) protein which inhibits induces( inhibits, induces ) smoothened patched( smoothened, patched ) protein which induces inhibits( induces, inhibits ) Gli/Ci activators repressors( activators, repressors ).

With Shh there are Gli/Ci activators repressors( activators, repressors ) and without Shh there are Gli/Ci repressors activators( repressors, activators ).

The archenteron blastocoel blastopore lip( archenteron, blastocoel, blastopore lip ) roof is responsible for anterior posterior( anterior, posterior ) patterns.
If it is transplanted to different locations of the early gastrula two heads emerge more motor neurons emerge two tails emerge( two heads emerge, more motor neurons emerge, two tails emerge ).

The forebrain is patterned by absence existence( absence, existence ) of Wnt activity.
Increasing Decreasing( Increasing, Decreasing ) Wnt concentration specifies more caudal CNS domains.

Retinoic acid is responsible for the expression of Hox Cre Otx Gbx( Hox, Cre, Otx, Gbx ) genes and posterior anterior dorsal ventral( posterior, anterior, dorsal, ventral ) patterning. Its concentration increases from anterior to posterior posterior to anterior( anterior to posterior, posterior to anterior ).

A lack of Notch activity would lead to more less( more, less ) neurons.

Stem cells are proliferating very slowly very fast( very slowly, very fast ) while progenitors proliferate much faster much slower( much faster, much slower ).