cerebellar granular layer development

Definition

Target type: biologicalprocess

The process whose specific outcome is the progression of the cerebellar granule layer over time, from its formation to the mature structure. The granular layer is the innermost layer of the cerebellar cortex. This layer contains densely packed small neurons, mostly granule cells. Some Golgi cells are found at the outer border. Granule neurons send parallel fibers to the upper molecular layer, where they synapse with Purkinje cell dendrites. Mossy fibers from the pontine nuclei in the white matter synapse with granule cell axons, Golgi cell axons and unipolar brush interneuron axons at cerebellar glomeruli in the granule cell layer. [GO_REF:0000021, GOC:cls, GOC:dgh, GOC:dph, GOC:jid, ISBN:0838580343]

The cerebellar granular layer, the largest neuronal population in the brain, undergoes a complex developmental process that begins with the generation of granule neuron precursors in the external granular layer (EGL) and culminates in the formation of a mature, densely packed granular layer. This process involves a series of intricate steps:

**1. Progenitor Proliferation and Migration:**
* The EGL is populated by proliferating granule neuron precursors, which are generated from radial glial cells in the ventricular zone.
* These precursors undergo extensive proliferation, increasing the population of granule neurons.
* As the EGL expands, granule neuron precursors migrate radially towards the internal granular layer (IGL) along Bergmann glial fibers.

**2. Differentiation and Maturation:**
* Upon reaching the IGL, granule neuron precursors undergo differentiation into mature granule neurons.
* This differentiation involves the expression of specific genes and proteins, such as calbindin, and the development of mature neuronal characteristics.
* Granule neurons establish synaptic connections with Purkinje cells, the major output neurons of the cerebellum, forming the parallel fibers.

**3. Synapse Formation and Circuit Refinement:**
* The formation of parallel fiber-Purkinje cell synapses is crucial for cerebellar function and is regulated by various factors.
* These synapses undergo refinement and plasticity during development, influenced by sensory input and activity-dependent mechanisms.
* This refinement process is essential for the fine-tuning of motor coordination and learning.

**4. EGL Elimination and Granule Layer Consolidation:**
* As the IGL matures, the EGL gradually disappears, reflecting the completion of granule neuron generation and migration.
* This elimination process is tightly regulated and involves apoptosis of the remaining EGL cells.
* The consolidation of the granular layer into a densely packed structure contributes to the highly organized architecture of the cerebellum.

The development of the cerebellar granular layer is a highly dynamic and regulated process that requires the coordinated interplay of multiple cellular and molecular events. This intricate development ensures the proper formation of the cerebellar circuitry, which is essential for motor coordination, balance, and learning.'
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