Abstract

Dopamine-synthesizing neurons located in the mammalian ventral midbrain are at the center stage of biomedical research due to their involvement in severe human neuropsychiatric and neurodegenerative disorders, most prominently Parkinson’s Disease (PD). The induction of midbrain dopaminergic (mDA) neurons depends on two important signaling centers of the mammalian embryo: the ventral midline or floor plate (FP) of the neural tube, and the isthmic organizer (IsO) at the mid-/hindbrain boundary (MHB). Cells located within and close to the FP secrete sonic hedgehog (SHH), and members of the wingless-type MMTV integration site family (WNT1/5A), as well as bone morphogenetic protein (BMP) family. The IsO cells secrete WNT1 and the fibroblast growth factor 8 (FGF8). Accordingly, the FGF8, SHH, WNT, and BMP signaling pathways play crucial roles during the development of the mDA neurons in the mammalian embryo. Moreover, these morphogens are essential for the generation of stem cell-derived mDA neurons, which are critical for the modeling, drug screening, and cell replacement therapy of PD. This review summarizes our current knowledge about the functions and crosstalk of these signaling pathways in mammalian mDA neuron development in vivo and their applications in stem cell-based paradigms for the efficient derivation of these neurons in vitro.

Highlights

  • The major dopaminergic (DA) neuronal population of the mammalian brain is located in the ventral midbrain (VM) [1]

  • Midbrain dopaminergic neurons are derived from a LMX1A/B (LIM homeobox transcription factor 1)- and FOXA1/2-positive progenitor domain that is established around day 9.5 of embryonic development (E9.5) at the ventral midline of the mesencephalon

  • We have summarized the current knowledge on the role of the four major signaling pathways and their known or putative interactions regulating the generation of midbrain dopaminergic (mDA) neurons in vivo and in vitro (Table 1)

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Summary

Introduction

The major dopaminergic (DA) neuronal population of the mammalian brain is located in the ventral midbrain (VM) [1]. Current in vitro differentiation protocols for mDA neurons are based on the activation of the three signaling pathways, FGF, SHH, and WNT, which regulate the formation of mammalian mDA neurons in vivo [12,42,43,44]. Understanding how these pathways interact is expected to critically increase the yield and quality of stem cell-derived mDA neurons. Signaling Pathways in Midbrain Dopaminergic Neuron Generation In Vivo and In Vitro

FGF Signaling Pathway in the Embryonic Midbrain
FGF-Regulated Developmental Processes in the mDA Neuron Progenitors
FGF Signaling Promotes mDA Neuron Differentiation In Vitro
The SHH Signaling Pathway
Expression of Shh Pathway Components in the Ventral Midbrain
Fate Mapping of SHH-Expressing and SHH-Responding Progenitors in the VM
In Vivo Function of the SHH Signaling Pathway
Function of SHH Signaling in the Generation of mDA Neurons from PSCs
WNT Signaling Pathways and Mechanisms
WNT Signaling in Mammalian mDA Neuron Development In Vivo
The BMP Signaling Pathway
BMPs in Stem Cell-Derived mDA Neuron Maturation
Crosstalk between SHH and WNT Pathways
Crosstalk between BMP and SHH Pathways
Findings
Conclusions
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