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

Abstract

Background: Midbrain dopaminergic neurons (mDA) play an important role in controlling the voluntary motor movement, reward behaviour and emotion-based behaviour. Differentiation of mDA neurons from progenitors depends on several 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 in mice embryo model, through in situ hybridization and immunohistochemistry 1) the possible role(s) of some SHH signalling 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-specific1) 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: At E12 and E14, but not E18, only Ptch1 and Gli1 were expressed in ventrolateral midbrain domains. All examined SHH signalling molecules were not detected in mDA area. Whereas, in MN9D cells, many SHH signalling molecules were expressed and co-localized with the 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. Besides, 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.