Résumé
The subgranular zone (SGZ) is a brain region in the hippocampus where adult neurogenesis occurs. The other major site of adult neurogenesis is the subventricular zone (SVZ) in the brain. The subgranular zone is a narrow layer of cells located between the granule cell layer and hilus of the dentate gyrus. This layer is characterized by several types of cells, the most prominent type being neural stem cells (NSCs) in various stages of development. However, in addition to NSCs, there are also astrocytes, endothelial cells, blood vessels, and other components, which form a microenvironment that supports the NSCs and regulates their proliferation, migration, and differentiation. The discovery of this complex microenvironment and its crucial role in NSC development has led some to label it as a neurogenic “niche”. It is also frequently referred to as a vascular, or angiogenic, niche due to the importance and pervasiveness of the blood vessels in the SGZ. The brain comprises many different types of neurons, but the SGZ generates only one type: granule cells—the primary excitatory neurons in the dentate gyrus (DG)--which are thought to contribute to cognitive functions such as memory and learning. The progression from neural stem cell to granule cell in the SGZ can be described by tracing the following lineage of cell types: Radial glial cells. Radial glial cells are a subset of astrocytes, which are typically thought of as non-neuronal support cells. The radial glial cells in the SGZ have cell bodies that reside in the SGZ and vertical (or radial) processes that extend into the molecular layer of the DG. These processes act as a scaffold upon which newly formed neurons can migrate the short distance from the SGZ to the granule cell layer. Radial glia are astrocytic in their morphology, their expression of glial markers such as GFAP, and their function in regulating the NSC microenvironment. However, unlike most astrocytes, they also act as neurogenic progenitors; in fact, they are widely considered to be the neural stem cells that give rise to subsequent neuronal precursor cells.
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Concepts associés (5)
Neurogenèse
La neurogenèse désigne l'ensemble du processus de formation d'un neurone fonctionnel du système nerveux à partir d'une cellule souche neurale. Elle a principalement lieu lors du développement neuronal du cerveau chez l'embryon et l'enfant (« neurogenèse primaire »). Certaines structures cérébrales des mammifères continuent cependant à produire des neurones chez l'individu adulte (). Issues du neuroectoderme, provenant lui-même de l'ectoderme, ces cellules migrent pendant la formation des structures du système nerveux central (tube neural puis vésicules cérébrales primitives : prosencéphale, mésencéphale et rhombencéphale).
Rostral migratory stream
The rostral migratory stream (RMS) is a specialized migratory route found in the brain of some animals along which neuronal precursors that originated in the subventricular zone (SVZ) of the brain migrate to reach the main olfactory bulb (OB). The importance of the RMS lies in its ability to refine and even change an animal's sensitivity to smells, which explains its importance and larger size in the rodent brain as compared to the human brain, as our olfactory sense is not as developed.
Reeline
La reeline est une protéine qui se trouve principalement dans le cerveau, mais aussi dans la moelle épinière, dans le sang et dans d'autres organes et tissus. Son gène est RELN, situé sur le chromosome 7 humain. Le nom est dû à la démarche titubante (reeling gait) des souris , dont on a découvert par la suite qu'elles présentaient une déficience en cette protéine cérébrale et étaient homozygotes pour la mutation du gène RELN, codant sa synthèse. Le principal phénotype associé à la perte de fonction reeline est une grossière inversion des couches corticales.
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