Figure 1. 5-HT_3AR is specifically expressed and upregulated in caudal ganglionic eminence (CGE)-derived interneurons (INs) during the phase of cortical invasion.

(a) Microdissection of cortical tissue (dotted lines) containing GAD65-GFP⁺ INs was performed at three developmental time points corresponding to the phase of tangential migration (E14.5), cortical invasion (E18.5) and termination of migration (P2.5). GAD65-GFP⁺ INs were isolated using fluorescence-assisted cell sorting (FACS) and gene expression analysis was performed using microarrays. (b) Microarrays revealed that Htr3a mRNA expression increases during cortical invasion in FACS-isolated GAD65-GFP⁺ INs (n=3 replicates at each time point). (c) Genetic fate mapping indicates that Htr3a-GFP⁺ INs only rarely (<%1) overlap with Nkx2.1-Cre; TOM⁺ cells and preferentially populate superficial cortical layers at P21 (n=4,636 Htr3a-GFP⁺ cells and 7,588 TOM⁺ cells in four brains). (d) The majority of Htr3a-GFP⁺ INs located in the mantle zone of the CGE at E14.5. CGE cells are immunolabelled for the CGE-enriched transcription factors COUP-TFII and/or SP8 (n=3,451 Htr3a-GFP⁺ cells in three brains). (e) Htr3a-GFP⁺ INs populate the CGE but not the medial ganglionic eminence (MGE) and migrate tangentially to reach the dorsal pallium through the subventricular zone (SVZ) stream (arrowheads). (f) In situ hybridization showing that the expression pattern of the Htr3a mRNA at E17.5 is similar to Htr3a-GFP⁺ mouse. Error bars are means±s.e.m. COUP-TFII, chicken ovalbumin upstream promoter transcription factor 2; Hst, Hoechst; LGE, lateral ganglionic eminence; VZ, ventricular zone. Scale bars: (a) 200 μm; (c) 50 μm; (d) 50 μm (low magnification), 10 μm (high magnification); (e,f) 200 μm.