Differential actions of the proneural genes encoding Mash1 and neurogenins in Nurr1-induced dopamine neuron differentiation

Abstract

The steroid receptor-type transcription factor Nurr1 has a crucial role in the development of the mesencephalic dopamine (DA) neurons. Although ectopic expression of Nurr1 in cultured neural precursor cells is sufficient in establishing the DA phenotype, Nurr1-induced DA cells are morphologically and functionally immature, suggesting the necessity of additional factor(s) for full neuronal differentiation. In this study, we demonstrate that neurogenic basic helix-loop-helix (bHLH) factors Mash1, neurogenins (Ngns) and NeuroD play contrasting roles in Nurr1-induced DA neuronal differentiation. Mash1, but not Ngn2, spatially and temporally colocalized with aldehyde dehydrogenase 2 (AHD2), a specific midbrain DA neuronal progenitor marker, in the early embryonic ventral mesencephalon. Forced expression of Mash1 caused immature Nurr1-induced DA cells to differentiate into mature and functional DA neurons as judged by electrophysiological characteristics, release of DA, and expression of presynaptic DA neuronal markers. By contrast, atonal-related bHLHs, represented by Ngn1, Ngn2 and NeuroD, repressed Nurr1-induced expression of DA neuronal markers. Domain-swapping experiments with Mash1 and NeuroD indicated that the helix-loop-helix domain, responsible for mediating dimerization of bHLH transcription factors, imparts the distinct effect. Finally, transient co-transfection of the atonal-related bHLHs with Nurr1 resulted in an E-box-independent repression of Nurr1-induced transcriptional activation of a reporter containing Nurr1-binding element (NL3) as well as a reporter driven by the native tyrosine hydroxylase gene promoter. Taken together, these findings suggest that Mash1 contributes to the generation of DA neurons in cooperation with Nurr1 in the developing midbrain whereas atonal-related bHLH genes inhibit the process.

Generation of Functional Dopamine Neurons from Neural Precursor Cells Isolated from the Subventricular Zone and White Matter of the Adult Rat Brain Using Nurr1 Overexpression

“…Nurr1 efficiently induced DA neurotransmitter identity in rat embryonic NP cells, but the Nurr1-induced DA cells were morphologically and functionally immature as presynaptic DA neurons [20,22,29]. Consistently, short or absent neurite extensions were observed from the THϩ cells differentiated from Nurr1-transduced precursor cells isolated from rat cortical tissues at E14 (Fig.…”

“…Nurr1 is an orphan nuclear receptor-type transcription factor with a critical role in midbrain DA neuron development that has been demonstrated in vivo [26 -28] and in vitro [19,20,22,29]. We retrovirally induced Nurr1 transgene expression in SVZ-and WM-derived NP cells using Nurr1-IRES-GFP or Nurr1-IRES-LacZ vector.…”

Differential and cooperative actions of Olig1 and Olig2 transcription factors on immature proliferating cells after contusive spinal cord injury

“…Recombinant retroviral vectors were constructed using the bicistronic retroviral vector pIRES-eGFP-CL, designed to express enhanced green fluorescent protein (GFP) as a marker of infected cells (Park et al, 2006). We generated Olig1 and Olig2 expression vectors by inserting the fulllengths Olig1 or Olig2 cDNAs into pIRES-eGFP-CL upstream of the IRES sequence.…”

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

“…2). Whereas Mashl is a general proneural gene, thought to act in a permissive manner (that is, dispensable, not required nor sufficient for DAn generation), Msxl and Ngn2 are essential for the correct development of VM DAn [6,17,18,23,27,[43][44][45][46][47].…”

“…[34]). MASH1 cooperates in a permissive manner in the generation of VM DAn, both in rodents and humans [23,27,46,47]. MSX1 prevents alternative cell fates through the repression of Nl<x6.1 and activates Ngn2 expression [6,24,43,45].…”