Spatiotemporal expression of sonic hedgehog signaling molecules in the embryonic mesencephalic dopaminergic neurons

Abstract

<jats:title>Abstract</jats:title> <jats:p>Background Midbrain dopaminergic neurons (mDA) play an important role in controlling the voluntary motor movement, reward behavior and emotion-based behavior. Differentiation of mDA neurons from progenitors depends on a number of secreted proteins, such as sonic hedgehog (SHH), and transcription factors. Different groups from mDA neurons arise from the varied patterns of SHH expression during development. The present study attempted to elucidate 1) the possible role(s) of some SHH signaling components (Ptch1, Gli1, Gli2 and Gli3) in the spatiotemporal development of mDA neurons along the rostrocaudal axis of the midbrain and their possible roles in differentiation (E12, E14) and survival of mDA neurons (E18); 2) the main role of Boc (bioregional Cdon-binding protein), and Gas1 (growth arrest-specific 1) as novel accessory receptors for the SHH in the development of mDA neurons 3) the significance of using the primary culture and/or the dopaminergic cell line (MN9D) for studying the development of mDA neurons. Results Mice embryos from embryonic day (E)12 were used for in situ hybridization and immunohistochemistry. The primary culture and cell line MN9D were used for <jats:italic>in vitro</jats:italic> investigation. At E12 and E14, but not E18, only Ptch1 and Gli1 were expressed in ventrolateral midbrain domains. All examined SHH signaling molecules were not detected in mDA area. Whereas, in MN9D cells, many SHH signaling molecules were expressed and co-localized with dopaminergic marker; tyrosine hydroxylase (TH), and their expression were upregulated with SHH treatment of the MN9D cells. Conclusion These results suggest that mDA neurons differentiation and survival are independent of SHH. In addition, MN9D cell line is not the ideal in vitro model for investigating the differentiation of mesencephalic dopaminergic neurons, and hence, the ventral midbrain primary culture might be favored over MN9D line.</jats:p>