Figure 2.

Expression of 13 genes in 18 neocortical regions, and the three divisions of the ganglionic eminences was obtained from RNA seq data, accessed via the database at http://brainspan.org/rnaseq/search/index.html from human fetal tissue aged 8 or 9 post-conceptional weeks; see Table S1 for more details. This figure is a summary of expression patterns observed. For the genes analysed, broadly speaking, expression patterns in the cortex fell into three categories represented by three coloured rectangles; higher expression anteriorly, laterally and ventrally (blue) or higher expression posteriorly and laterally (green) or higher expression anteriorly and medially compared to laterally (turquoise). Four patterns of expression were observed in the ganglionic eminences; equal expression across the ganglionic eminences (orange) higher expression in the MGE (dark red) or higher expression in the CGE (dark yellow). The resulting Venn diagram divides the expression of 13 genes (in italics) between five points of overlap. We propose that a component of the higher expression of some GABAergic genes in the anterior/lateral/ventral cortex derives from a subset of GABAergic precursors generated in the pallium specified by antero-ventral signalling, whereas higher expression of some cortical GABAergic genes in lateral and posterior regions likely derives entirely from inwardly migrating cells (see text for more details). The expression pattern of NGN2 and SP8 is quite different from the rest reflecting their primary roles in determination of glutamatergic identity (NGN2, Wilkinson et al. 2013) and anterior/medial identity (SP8, O’Leary & Sahara, 2008) in the pallium at this stage of development.