The fore brain, mid brain and the hind brain are the main sections of the brain, all with unique functions. They develop from the embryonic stage to the end of the brain development process.  Concepts such as brain patterning and networking are crucial to understand in the analysis of the contribution of organizers in brain development. Each part of the brain develops independently from other areas under the influence of an organizer. This is a group of cells that have the ability to induce new fate in neighboring cells and pattern the induced and other neighboring tissues. Organizers form when one’s central nervous system develops and controls elevated patterning of various brain regions. This involves generating cellular diversity in a vertebrate brain referred to as regionalization, which involves two steps.

The first step involves an establishment of cell populations such as floor plates or isthmic organizers, which are local sources of signals within neuroectoderm. The second step involves modulation and refining initial regional patterning through secondary organizers. Under these circumstances, expression domains of newly induced genes begin subdivision of one’s neural plate. As a result, there are discrete territories that prefigure various structures of a mature central nervous system. Principal organizers or signaling centers set up at morphological boundaries between distinct brain territories. These organizers include;

• Isthmic organizer located in the basal forebrain between rostal and caudal in the Central Nervous System.
• Floor plate and roof plate located on dorsal and ventral ends of the neural tube.
• Midbrain-hindbrain boundary located in the brain’s rostral end.

Midbrain-hindbrain Boundary organizer

This organizer acts on midbrain and hindbrain primordial. Research carried out with Midbrain-Hindbrain Boundary Organizer transplanted into the caudal forebrain of the chick embryo. This shows surrounding host tissues switch fate and adopt a midbrain character. Conclusions suggest that the hindbrain and midbrain boundary organizer plays a vital organizing centre in its location.  In the early embryonic stages, several genes encoding either transcription or secreted proteins are expressed within the midbrain hindbrain. During this establishment, at least three signaling pathways are activated independently of each other. The maintenance phase follows the establishment phase, whereby genes commence to depend on each other.  Perturbation of any gene disrupts continued development of midbrain hindbrain boundary and endows cells with organizing capacity. Organizer derived signals are necessary for proper polarization of midbrain retinotectal map. They enable it to maintain its integrity and that of the cerebellum while setting anterior limit of the Hox gene in the hindbrain. As a result, they determine the development of the tectum, tegmentum and cerebellum through the release of the Fgf8 protein gene.

Zona Limitans Intrathalamica

Zona Limitans Intrathalamica is located in a border sandwiched between the prethalamus and thalamus in subsequent vertebrates. It functions as a mid-diencephalic organizer (MDO) by secreting the sonic hedgehog signaling factor. The MDO directs acquisition of cellular identity in the surrounding diencephanon (the brain region that mainly includes thalamus) through release of Sonic Hedgehog (shh) protein. Amphioxus and Ciona both have a deficieny in the hedgehog ZLI-like expression domain located in anterior nerve cord. This expression is highly evocative to the vertebrate. In zebrafish, it is arguable that the ZLI formation relies on the otx function. This demonstrates that the patterning function is present in these signaling centers.

Anterior Neural Ridge

Anterior Neural Ridge is located at a rostral end of a vertebrate’s neural plate. It induces the anterior forebrain through secretion of Fgf8 cells and Wnt inhibitors, which give rise to commissural plates. During the later stages, the Fgf8 triggers a neocortical primordium signalling recognition commencing from the commissural plate. Functionalities centered on Molecular mechanisms present a slim variation. This is regardless the fact that ANR is billed to be present in all studied vertebrates. The secreted protein compositions that include Wnt inhibitors are expressed inside the mouse ANR although the evidence is not convincing to date. It is probable that various Wnt inhibitors source inducing signals have shifted between different vertebrates. They are: ANR in zebrafish, prechordial plate in amphibians, anterior visceral endoderm and prechordal plate in amniotes.

Notorchord

Notochord is a rod of dorsal mesorderm derived from the spermann’s organizer, which regulates ventral neural patterning. The notorchord and prechordal plate are necessary for ventral CNS identity induction while Shh serves as the core signalling factor in this process mediation. Vertebrates have a broader mesendodermal tissue with different signaling properties while prechordal plate’s position is the notochord’s anterior end.

Floor Pate and Roof Plate

The Floor Plate comprise of non-neural cells stripped along the ventral midline in vertebrates. It controls the ventral neural patterning in addition to axon guidance by Shh expressions. It couples this with other factors that include Netrin. On the other hand, the roof plate patterns and develops vertebrate neural tube through sending dorsal neuron signals. However, there is no clear definition of the roof plate signaling mechanism, although experiments disrupting signals Bmps and Wnts show different results. Research indicates that this might be due to functional redundancy. There is minimal proof for a presence of roof plate Bmp and Wnt secretors in nonvertabrate embryos. Bmp signaling in amphioxus and ciona assists in peripheral sensory neurons function stipulations. A similarity is noted in vertebrates where placodes and the neural crest situated at the neural plate’s border births neurons. A neural patterning function nevertheless remains established for them.

Isthmic Organizer

The Isthmic Organizer controls development of the anterior hindbrain and midbrain, and expresses signaling molecules, which are FGF8 and Wnt1. The boundary of the brain’s anterior and posterior parts induces the FGF8 molecule, which patterns neocortex and the midbrain.  The brain is a component of the central nervous system that has networks, whose development takes place through patterning. It involves organizers in one’s brain also signaling centers, releasing proteins while establishing tegmentum and cerebellum.  In human beings, there is a correlation between brain organizers and senses such as touch, visual abilities, and audio abilities. They relate to an individual’s outward reactions, an aspect that develops right from birth.

Organizers in the brain foster development by regulating the death of cells. Two major events that enable establishment of mature brain architecture and connectivity include neuronal cell decline and axon pruning. Axon guidance cues regulate regressive events in definitive models of neural development. This occurs from early control of apoptosis of neural progenitor, to a later maintenance that is centered on the neuronal survival. Additionally, it assists in the stereotyped pruning of axonal branches. The field’s vital challenge is identifying the extent at which different guidance cues join at analogous intracellular pathways. This is aimed at checking cell death and presumed survival, in addition to axon regulation and pruning.

The pathways of PCD are not confined to a late role of destroying cells after the damage takes place, but are involved from the beginning. The molecular level of programmed cell death pathways is now understood in detail. However, there is need to explore the PCD canonical pathways and explore the axon destruction mechanism. Cell death pathways are characterized by: the mitogen-activated protein kinase signaling cascade and cyclin-dependent kinase 5-mediated phosphorylation of myocyte enhancer factor 2. In animals the pathway blockade has achieved a level of neuroprotection of neuron cell soma. In contrast, axon protection has been hard to come by. All new concepts of PCD offer opportunities for development of new approaches to neuroprotective therapeutics.

Development of nervous system involves regressive as well as progressive events. Progressive events are identified as neurite outgrowth, neural proliferation and synapse formation. Their main aim is to prep up an extensive blueprint of neural connectivity. Consequently, regressive events outlined as axon pruning, cell death and synapse elimination are fundamental in refining the pattern to a more clear-cut and established mode of circulation. Mutations occurring in the apoptotic pathway can effect a growth of brain centered morphological defects. They result in the lethal distraction of neuronal growth. Consequently, axon pruning is known to affect the neuronal network culminating to brain dysfunction at later stages.

In conclusion, the brain’s patterning principles have their basis on signals from organizers. During and after gastrulation, organizer centers and their mesodermal derivatives send signals for neural induction and anterior fate. Organizers are necessary for brain and physical development through the release of essential proteins. Differentiation, which involves segmentation and the formation of a neural tube, takes place during brain development.

 

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