Fig. 1. Helt is selectively expressed in GABAergic progenitors in the developing mouse mesencephalon. (A) Comparison of the expression pattern of Helt with those of transmitter markers in the mesencephalon at E11.5 and E12.5. The lower panels show the dorsal mesencephalon region at E12.5. Helt is selectively expressed in GABAergic domains and excluded from glutamatergic domains. In the dorsal m1 domain, only glutamatergic neurons are generated and Helt is not expressed in the VZ at E11.5. At later stages, both GABAergic and glutamatergic neurons are generated, and Helt is expressed by subpopulations of the dorsal progenitors. (B) Domain structure of the developing mesencephalon. The expression patterns of transcription factors in the E11.5 mesencephalon are shown. Each domain is indicated as m1 to m7 (summarized in Fig. 2). Helt is expressed in the ventricular zone (VZ) of the m2 to m7 domains. Note that some Helt⁺ cells are observed in the ventral-most region of the m1 domain at E11.5. These Helt⁺ cells in the m1 domain are not obvious in embryos at a slightly earlier stage (data not shown).