Analysis of embryonic motoneuron gene regulation: derepression of general activators function in concert with enhancer factors.
The underlying transcriptional mechanisms that establish the proper spatial and temporal pattern of gene expression required for specifying neuronal fate are poorly defined. We have characterized how the Hb9 gene is expressed in developing motoneurons in order to understand how transcription is directed to specific cells within the developing CNS. We found that non-specific general-activator proteins such as E2F and Sp1 are capable of driving widespread low level transcription of Hb9 in many cell types throughout the neural tube; however, their activity is modulated by specific repressor and activator complexes. The general-activators of Hb9 are suppressed from triggering inappropriate transcription by repressor proteins Irx3 and Nkx2.2. High level motoneuron expression is achieved by assembling an enhancesome on a compact evolutionarily-conserved segment of Hb9 located from -7096 to -6896. The ensemble of LIM-HD and bHLH proteins that interact with this enhancer change as motoneuron development progresses, facilitating both the activation and maintenance of Hb9 expression in developing and mature motoneurons. These findings provide direct support for the derepression model of gene regulation and cell fate specification in the neural tube, as well as establishing a role for enhancers in targeting gene expression to a single neuronal subtype in the spinal cord.
Lee
Soo-Kyung
SK
Gene Expression Laboratory, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
Jurata
Linda W
LW
Funahashi
Junichi
J
Ruiz
Esmeralda C
EC
Pfaff
Samuel L
SL
D000818:Animals; D001483:Base Sequence; D018797:Cell Cycle Proteins; D002460:Cell Line; D019070:Cell Lineage; D002490:Central Nervous System / Q000196:embryology*; D002642:Chick Embryo; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D050684:E2F Transcription Factors; D018274:Electroporation; D004742:Enhancer Elements, Genetic; D005091:Exons; D018507:Gene Expression Regulation, Developmental; D049452:Green Fluorescent Proteins; D000090322:Homeobox Protein Nkx-2.2; D018398:Homeodomain Proteins / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D008164:Luminescent Proteins / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009046:Motor Neurons / Q000378:metabolism*; D009432:Neural Crest / Q000196:embryology; D009474:Neurons / Q000378:metabolism; D009687:Nuclear Proteins; D014176:Protein Biosynthesis; D012689:Sequence Homology, Nucleic Acid; D016329:Sp1 Transcription Factor / Q000378:metabolism; D013116:Spinal Cord / Q000196:embryology; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection; D019076:Transgenes; D029961:Zebrafish Proteins
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D000090322:Homeobox Protein Nkx-2.2; D018398:Homeodomain Proteins; C501598:IRX3 protein, human; C501599:Irx3 protein, mouse; D008164:Luminescent Proteins; C490003:MNX1 protein, human; C000715631:NKX2-2 protein, human; C000715627:Nkx2-2 protein, mouse; D009687:Nuclear Proteins; D016329:Sp1 Transcription Factor; D014157:Transcription Factors; D029961:Zebrafish Proteins; C000715630:nkx2.2b protein, zebrafish; C084059:Hb9 protein, mouse; D049452:Green Fluorescent Proteins; D004247:DNA