Neural crest patterning: autoregulatory and crest-specific elements co-operate for Krox20 transcriptional control.
Neural crest patterning constitutes an important element in the control of the morphogenesis of craniofacial structures. Krox20, a transcription factor gene that plays a critical role in the development of the segmented hindbrain, is expressed in rhombomeres (r) 3 and 5 and in a stream of neural crest cells migrating from r5 toward the third branchial arch. We have investigated the basis of the specific neural crest expression of Krox20 and identified a cis-acting enhancer element (NCE) located 26 kb upstream of the gene that is conserved between mouse, man and chick and can recapitulate the Krox20 neural crest pattern in transgenic mice. Functional dissection of the enhancer revealed the presence of two conserved Krox20 binding sites mediating direct Krox20 autoregulation in the neural crest. In addition, the enhancer included another essential element containing conserved binding sites for high mobility group (HMG) box proteins and which responded to factors expressed throughout the neural crest. Consistent with this the NCE was strongly activated in vitro by Sox10, a crest-specific HMG box protein, in synergism with Krox20, and the inactivation of Sox10 prevented the maintenance of Krox20 expression in the migrating neural crest. These results suggest that the dependency of the enhancer on both crest- (Sox10) and r5- (Krox20) specific factors limits its activity to the r5-derived neural crest. This organisation also suggests a mechanism for the transfer and maintenance of rhombomere-specific gene expression from the hindbrain neuroepithelium to the emerging neural crest and may be of more general significance for neural crest patterning.
Ghislain
Julien
J
Unité 368 de l'Institut National de la Santé et de la Recherche Médicale, Ecole Normale Supérieure, 46 rue d'Ulm, 75230 Paris Cedex 05, France.
Desmarquet-Trin-Dinh
Carole
C
Gilardi-Hebenstreit
Pascale
P
Charnay
Patrick
P
Frain
Monique
M
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D019521:Body Patterning; D002642:Chick Embryo; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D051767:Early Growth Response Protein 2; D004622:Embryo, Mammalian / Q000033:anatomy & histology / Q000502:physiology; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D018507:Gene Expression Regulation, Developmental; D017930:Genes, Reporter; D006609:High Mobility Group Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D017403:In Situ Hybridization; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D008822:Mice, Transgenic; D008957:Models, Genetic; D009024:Morphogenesis; D009432:Neural Crest / Q000033:anatomy & histology / Q000502:physiology*; D055757:SOXE Transcription Factors; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
D004268:DNA-Binding Proteins; C497326:EGR2 protein, human; D051767:Early Growth Response Protein 2; C497327:Egr2 protein, mouse; D006609:High Mobility Group Proteins; C527923:SOX10 protein, human; D055757:SOXE Transcription Factors; C527924:Sox10 protein, mouse; D014157:Transcription Factors