Figure 2. Gene expression patterns in the subpallium.

Drawings of medial (A), caudal-intermediate (B) and caudal (C) coronal sections of E13.5 mouse brain showing the expression of different genes in the subpallial domain which give rise to distinct interneuron subpopulations. Broken lines delineate the VZ. Sub-domains that express two or more genes are marked with stripes. (A and B) Pax6 is expressed at high levels in the pallial proliferative zone and thalamic territory, and at a lower level in the subpallial proliferative zone of the LGE. Nkx2.1 is specifically expressed in the VZ and mantle layer of the MGE. It is also expressed in the proliferative zone of the AEP/POA. Nkx6.2 expression is confined to the LGE/MGE border and overlaps with the expression of Pax6/Dlx2 in the LGE, and Nkx2.1/Dlx2 in the MGE. CR+ (CR-positive) and SST+ (SST-positive) interneuron precursors arise specifically from this Nkx6.2/Nkx2.1-expressing territory. Lhx6 expression is confined to the subventricular zone and the mantle layer of the MGE, and it specifies PV+ (PV-positive) interneurons. Its expression does not overlap with Nkx6.2 expression. AEP/POA, thought to give rise to NPY+ (NPY-positive) interneurons, expresses Nkx2.1, Dlx2 and Nkx5.1, as well as Nkx6.2 in its ventral domain. (C) The CGE is anatomically positioned at the most caudal part of the telencephalon where the LGE and MGE fuse. It remains a matter of debate which genes are specifically expressed in this territory. However, abundant evidence indicates that the CGE generates CR+ interneurons. Shown here is the expression of Dlx2, which characterizes all subpallial domains, Pax6 confined to the proliferative zone, and Lhx6. (D) A summary of the expression of different genes in the LGE, MGE, CGE and POA. ++, High level of expression: +, lower level of expression; -, lack of expression. Abbreviations: Gp, globus pallidus; H, hippocampus; NCx, neocortex; St, striatum; Th, thalamus.