.
The GE may initiate migration because it expresses molecules that repulse interneurons. Semaphorins sema3a and sema3f in the lGE that affect interneurons through the neuropilins and plexin coreceptors. Chondrotin-4-sulfate work in coordination with semaphorins to propel interneurons through the lGE \cite{Kelsom_2013}. The downregulation of Nkx2.1 appears to be important for the normal migration of interneurons from the MGE because ectopic Nkx2.1 appears to lead in a disfunction in Sema3a and Sema3f (CITATION).
Slit1 also acts as a chemorepellent through the Roundabout (robo1) receptor on cortical interneurons \cite{Kelsom_2013}. Finally, ephrin and the ephrin receptor tyrosine kinases on interneurons also act as repulsive signal for MGE derived interneurons. CHECK SENTENCE ephrin 5a in the ventricular zone of the GE and receptor Epha4 is expressed by calbindin-expressing MGE-derived interneurons. \cite{Kelsom_2013}
Neuregulin 1 (Nrg1) is a protein (?) produced in the cortex that can guide mGE interneurons through the lGE and to the cerebral cortex. It has an epidermal growth-factor (EGF) domain that can activate the tyrosine kinase receptor ErB4 in interneurons \cite{Mar_n_2015}. Multiple types of Nrg1 can be expressed by the cortex and can have various effects \cite{Mar_n_2015} by modifying how interneurons extend neurites to produce their migration.
Another chemoattractant in the cortex is chenokine CXCL12 which changes over the course of embryonic development \cite{Kelsom_2013} . While it starts off high in the marginal zone and subventricular zone, it decreases in the subventricular zone. Interneurons from the mGE express CXCR4 and CXCR7 receptors \cite{Kelsom_2013} and are guided by CXCL12 to the cortex.
While interneurons have highly segregated distribution patterns in cortical layers, it is not yet clear how interneurons determine their terminal emplacement. Interneurons from the MGE do appear to form the cortex in an inside-out manner. One hypotheis suggests that early interneurons follow cues from infragranular pyramidal layers (V-VI), whereas interneurons that are born later are signalled by cues from supragranular layers (II-IV) (Marin 2015)