Expression analyzes of early factors in midbrain differentiation programs.

Mesodiencephalic dopaminergic (mdDA) neurons are born in the ventricular zone (VZ) of the midbrain between E10 and E12. Although these neurons all express specific DA markers like Th and Pitx3, they are subdivided into distinct subsets, each depending on a unique set of transcription factors and signaling cascades for their differentiation. How a neural progenitor commits to an mdDA neuronal cell-fate and how the specification into the different subsets is determined remains unclear. To gain more insight into the development and specification of these neurons we have previously conducted a genome-wide expression analysis, in which dissected midbrain material (E10.5-E13.5) was compared to the adult mdDA region (Chakrabarty et al., 2012). In the present study, we have compared the genome-wide expression analysis including PITX3-GFP sorted (E12.5-E15.5) neurons to available expression data to search for genes specifically expressed in the midbrain during early stages of mdDA differentiation. We have divided these genes into 3 groups: (I) genes upregulated throughout differentiation (Mest, NeuroD1, and Tcf12), (II) genes upregulated during early stages of differentiation (Hes5, and Tcf3), and (III) genes upregulated during late stages of differentiation (Enc1). Here, we show the expression profile of these genes in the embryonic midbrain during development and adult stage and compared that to the appearance of mdDA neurons via co-staining for TH. With this analysis we have identified 6 novel factors that may play a role during cell-fate commitment of neural progenitors or later during differentiation of the mdDA group of neurons.