Identification of midbrain floor plate radial glia‐like cells as dopaminergic progenitors

Abstract

The floor plate (FP), a signaling center and a structure rich in radial glia-like cells, has been traditionally thought to be devoid of neurons and neuronal progenitors. However, in the midbrain, the FP contains neurons of the dopaminergic (DA) lineage that require contact with radial glia-like cells for their induction. We, therefore, decided to explore the interaction relationship between radial glia and neurons during DA neurogenesis. Taking advantage of a novel FP radial glia-like cell culture system and retroviruses, DA neurons were lineage traced in vitro. In utero BrdU pulse-chases extensively labeled the midbrain FP and traced DA neurons both in vivo and in FP cultures. Moreover, from E9.5 to E13.5 the midbrain FP contained dividing cells only in the most apical part of the neuroepithelium, in cells identified as radial glia-like cells. We, therefore, hypothesized that midbrain FP radial glia-like cells could be DA progenitors and tested our hypothesis in vivo. Lineage tracing of DA progenitors with EGFP in Tis21-EGFP knock-in mice, and genetic fate mapping in GLAST::CreERT2/ZEG mice identified the neuroepithelium of the midbrain FP, and specifically, GLAST+ radial glia-like cells as DA progenitors. Combined, our experiments support the concept that the midbrain FP differs from other FP regions and demonstrate that FP radial glia-like cells in the midbrain are neurogenic and give rise to midbrain DA neurons.

How to make a midbrain dopaminergic neuron

“…Fate mapping experiments have indicated that mDA neurons originate from progenitors sorted for the FP marker CORIN (Ono et al, 2007) or expressing the radial glia marker Glast/Slc1a (glial high affinity glutamate transporter) (Bonilla et al, 2008). This shows that mFP radial glial cells, unlike FP radial glia in other brain regions, can undergo neurogenesis and are mDA progenitors.…”

Human midbrain precursors activate the expected developmental genetic program and differentiate long-term to functional A9 dopamine neurons in vitro. Enhancement by Bcl-XL

“…1 and 2) must activate genes required for the development of a correct A9-DA phenotype, at a time in the mouse when the cells exit the cell cycle [21,22]. Nurrl expression in the mouse (cooperating with Pitx3) is critical for the acquisition of the correct DA phenotype (that requires co-expression of TH, AADC, VMAT2 and DAT) [17,22,73,74].…”

“…VM DAn originate from precursors residing in the mesencephalic floor plate (FP), both in rodents and humans, which show features of radial glia [9][10][11][12], reviewed by [6,[13][14][15][16][17][18][19][20][21][22][23][24]. In spite of the importance of identifying a well-characterized and reliable source of human A9-DAn, the present situation is that all neural stem/precursor cultures explored so far present numerous limitations.…”

Building authentic midbrain dopaminergic neurons from stem cells - lessons from development

“…The lack of success in generating functional DA neurons of a mesencepahlic identity was explained when it was revealed that mesDA neurons have their cellular origin from the midbrain floor plate rather than from the neuroepithelium and that the floor plate transcription factor FOXA2 is an important gene necessary for correct mesDA specification and maintenance [16][17][18][19]. In rodents and humans, The enzyme tyrosine hydroxylase (TH) is a required enzyme for DA synthesis, and is often used as a key marker of DA neurons.…”