The mGE is the main progenitor region for interneurons with approximately 55% of cortical interneurons originating from this location in mice \cite{Kelsom_2013}. There are two main types of interneurons that are produced in the mGE based on transmembrane proteins that they uniquely express. These interneurons either express Parvalbumin (PV), which promotes prolonged rapid depolarization, or somatostatin (SST), which favors burst firing or slower depolarizations \cite{Mar_n_2015}. The expression of the Nkx2.1 gene, which is modulated by the level of of Sonic Hedgehog (Shh) signalling, is unique to the mGE and dictates whether an interneuron will express SST or PV \cite{Kelsom_2013}. The complete or even partial loss of Nkx2.1 leads to a significant decrease in the number of PV and SST interneurons. It is still unknown the "extent of the spatial segregation" of these types of interneurons within the mGE \cite{Kelsom_2013}.
Nkx2.1 expression dictates the generation of both PV- and SST expressing MGE progeniators and the maintenance of Nkx2.1 expression is activated by Shh signaling. More specifically, the level of Shh signaling within MGE interneuronal prohenitor cells seems to be determinant of what marker these neurons will express, either PV or SST: Xu et al have shown that high levels of Shh signaling preferentially give rise to SST-epxressing interneurons, which in turn results in reduced production of PV-expressing interneurons. Compete absence or conditional loss of Nkx2.1 results in reduction of PV and SST expressing interneurons, demonstrating its importance for MGE derived interneuronal specification. \cite{Kelsom_2013} The Lhx6 gene is also implicated with the specification of interneurons through a downstream interaction with Nxk2.1 \cite{Kelsom_2013}.
cGE is a bit of a hybrid between the MGE and LGE. cGE is second largest contributor of interneurons, producing approximately 30-40% of all cortical interneurons. (Marin 2015)