GABAergic differentiation induced by Mash1 is compromised by the bHLH proteins Neurogenin2, NeuroD1, and NeuroD2.
During forebrain development, Mash1 directs gamma-aminobutyric acid (GABA)ergic neuron differentiation ventrally in the ganglionic eminences. Repression of Mash1 in the cortex is necessary to prevent the formation of GABAergic interneurons. Negative regulation of Mash1 has been attributed to members of the Neurogenin family; the genetic ablation of Neurogenin2 (Ngn2) leads to the derepression of Mash1 and the formation of ectopic GABAergic neurons in the cortex. We have developed an in vitro system to clarify the importance of NeuroD proteins in the Mash1 regulatory pathway. Using a neurosphere culture system, we show that the downstream effectors of the Ngn2 pathway NeuroD1 and NeuroD2 can abrogate GABAergic differentiation directed by Mash1. The ectopic expression of either of these genes in Mash1-expressing cells derived from the lateral ganglionic eminence, independently downregulate Mash1 expression without affecting expression of distal less homeodomain genes. This results in a complete loss of the GABAergic phenotype. Moreover, we demonstrate that ectopic expression of Mash1 in cortical progenitors is sufficient to phenocopy the loss of Ngn2 and strongly enhances ectopic GABAergic differentiation. Collectively, our results define the compensatory and cross-regulatory mechanisms that exist among basic helix-loop-helix transcription factors during neuronal fate specification.
Roybon
Laurent
L
Neuronal Survival Unit, Department of Experimental Medical Science, Wallenberg Neuroscience Center, 221 84 Lund, Sweden. lr2491@columbia.edu
Mastracci
Teresa L
TL
Ribeiro
Diogo
D
Sussel
Lori
L
Brundin
Patrik
P
Li
Jia-Yi
JY
D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects; D002454:Cell Differentiation / Q000502:physiology*; D002478:Cells, Cultured; D003857:Deoxyuridine / Q000378:metabolism; D051937:Dopamine and cAMP-Regulated Phosphoprotein 32 / Q000378:metabolism; D004622:Embryo, Mammalian; D005260:Female; D015870:Gene Expression / Q000235:genetics*; D049452:Green Fluorescent Proteins / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000502:physiology*; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism*; D011247:Pregnancy; D051381:Rats; D017207:Rats, Sprague-Dawley; D013234:Stem Cells / Q000502:physiology; D013997:Time Factors; D014161:Transduction, Genetic / Q000379:methods; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D051792:Basic Helix-Loop-Helix Proteins; D003857:Deoxyuridine; D051937:Dopamine and cAMP-Regulated Phosphoprotein 32; D049452:Green Fluorescent Proteins; D009419:Nerve Tissue Proteins; D009479:Neuropeptides; D005680:gamma-Aminobutyric Acid; C499317:Ascl1 protein, mouse; C501008:Neurod1 protein, mouse; C098995:Neurod2 protein, mouse; C102938:Neurog2 protein, mouse