Medial ganglionic eminence (MGE)
The primary purpose of the MGE during development is to produce GABAergic stellate cells and direct their migration to the neocortex.[6] The precursors of most GABAergic interneurons in the cerebral cortex migrate from the subcortical progenitor zone. More specifically, performing a mechanical transection of the migratory route from the MGE to the neocortex causes a 33% decrease in GABAergic interneurons in the neocortex.[6] The MGE also produces some of the neurons and glia of the basal ganglia and hippocampus.[6][7] The MGE may also be a source of Cajal-Retzius cells, but this remains controversial.[6] Early in embryonic development, the interneurons in the cortex stem primarily from the MGE (mouse evidence!) [8] and the AEP. In vitro experiments show that MGE cells migrate more than 300 μm per day, three times faster than the migration of LGE cells.[2] See more about the time frame and function of MGE in comparison to the LGE in the following section.
Lateral ganglionic eminence (LGE)
Compared to the early temporal frame of development in the MGE, the LGE aids in the tangential migration of cells later in the mid-embryogenic stage. Unlike the MGE, which guides most cell migration into the cortex during this stage, the LGE contributes less to cell migration to the cortex, and instead guides many cells to the olfactory bulbs. In fact, the migration to the olfactory bulb is led by the LGE into adulthood. The route that newly generated neurons take from the anterior subventricular zone to the olfactory bulb is called the rostral migratory stream. During the late stages of embryonic development, both the LGE and MGE guide cell migration to the cortex, specifically the proliferative regions of the cortex.[2] Some studies have found that the LGE also contributes cells to the neocortex, but this remains an issue of debate.[6] In vitro, cells migrating from the LGE travel at a rate of 100 μm per day, slower than the MGE cells.[2]
Caudal ganglionic eminence (CGE)
The caudal ganglionic eminence is another subcortical structure that is essential to the generation of cortical interneurons. It is located next to the lateral ventricle, posterior to where the LGE and MGE fuse. The CGE is a fusion of the rostral medial and lateral ganglionic eminence, which begins at the mid to caudal thalamus. There are two molecular domains that exist within the CGE and closely resemble extensions of the caudal MGE and LGE.[9] The CGE is distinct from the LGE and MGE in gene expression patterns and progeny produced. Unlike the cells from the MGE, the cells from the CGE were rarely parvalbumin-containing neurons. It seems that the majority of cells from the CGE were GABAergic interneurons, but depending on where they are located, CGE-derived cells are very diverse. CGE-derived cells include GABAergic interneurons, spiny interneurons, mossy cells, pyramidal and granule neurons, and even oligodendrocyte and astrocyte glial cells.[6]
