Ganglionic Eminence - Categorization

Categorization

Ganglionic eminences are categorized into three groups based their on location within the subventricular zone:

• Medial ganglionic eminence (MGE)
• Lateral ganglionic eminence (LGE)
• Caudal ganglionic eminence (CGE)

A sulcus separates the medial and lateral ganglionic eminences. The expression of Nkx2-1, Gsx2, and Pax6 is required to determine the independent progenitor cell populations in the LGE and MGE. Interactions between these three genes define the boundaries between the different progenitor zones and mutations of these genes can cause abnormal expansion around the MGE, LGE, ventral pallium (VP), and anterior entopeduncular region (AEP). The cells of the GEs are quite homogenous, with the MGE, LGE, and CGE all having small, dark, irregular nuclei and moderately dense cytoplasm, however, each eminence can be identified by the type of progeny that it produces. See the individual GE sections below for more information on the different types of progeny produced.

Additionally, the subventricular zone is the starting point of multiple streams of tangentially migrating interneurons that express Dlx genes. There are three main tangential migration pathways that have been identified in this region:

1. the latero-caudal migration (subpallial telencephalon to cortex)
2. the medio-rostral migration (subpallial basal telencephalon to the olfactory bulb)
3. the latero-caudal migration (basal telencephalon to the striatum)

These pathways are temporally and spatially distinct, and produce a variety of GABAergic, and non-GABAergic interneurons. One example of GABAergic interneurons that the GEs guide are parvalbumin-containing interneurons in the neocortex. Some examples of non-GABAergic interneurons that the GEs guide are dopaminergic interneurons in the olfactory bulb, and cholinergic interneurons in the striatum. Cells migrating along these pathways move at different rates. Some molecules that have been implicated in controlling the rate of the unidirectional movement of cells derived from the GEs are hepatocyte growth factor/scattered factor (HGF/SF), and variousneurotrophic factors.