Three enhancer regions regulate gbx2 gene expression in the isthmic region during zebrafish development

Islam, M.E., Kikuta, H., Inoue, F., Kanai, M., Kawakami, A., Parvin, M.S., Takeda, H., and Yamasu, K.
Mechanisms of Development   123(12): 907-924 (Journal)
Registered Authors
Inoue, Fumitaka, Islam, Md. Ekramul, Kawakami, Atsushi, Kikuta, Hiroshi, Takeda, Hiroyuki, Yamasu, Kyo
Brain formation, DDC model, gbx2, Isthmus, Midbrain–hindbrain boundary, Promoter analysis, Transcription, Zebrafish
MeSH Terms
  • Animals
  • Base Pairing
  • Binding Sites
  • Enhancer Elements, Genetic/genetics
  • Enhancer Elements, Genetic/physiology*
  • Gene Expression Regulation, Developmental*
  • Genes, Reporter
  • Genome, Insect
  • Green Fluorescent Proteins/analysis
  • Green Fluorescent Proteins/genetics
  • Homeodomain Proteins/genetics*
  • Mesencephalon/metabolism
  • Molecular Sequence Data
  • PAX2 Transcription Factor/genetics
  • PAX2 Transcription Factor/metabolism*
  • Rhombencephalon/metabolism
  • Transcription Factors/metabolism
  • Transcription, Genetic
  • Zebrafish/embryology*
  • Zebrafish/genetics
  • Zebrafish Proteins/genetics*
17067785 Full text @ Mech. Dev.
In vertebrate embryos, positioning of the boundary between the midbrain and hindbrain (MHB) and subsequent isthmus formation are dependent upon the interaction between the Otx2 and Gbx genes. In zebrafish, sequential expression of gbx1 and gbx2 in the anterior hindbrain contributes to this process, whereas in mouse embryos, a single Gbx gene (Gbx2) is responsible for MHB development. In the present study, to investigate the regulatory mechanism of gbx2 in the MHB/isthmic region of zebrafish embryos, we cloned the gene and showed that its organization is conserved among different vertebrates. Promoter analyses revealed three enhancers that direct reporter gene expression after the end of epiboly in the anterior-most hindbrain, which is a feature of the zebrafish gbx2 gene. One of the enhancers is located upstream of gbx2 (AMH1), while the other two enhancers are located downstream of gbx2 (AMH2 and AMH3). Detailed analysis of the AMH1 enhancer showed that it directs expression in the rhombomere 1 (r1) region and the dorsal thalamus, as has been shown for gbx2, whereas no expression was induced by the AMH1 enhancer in other embryonic regions in which gbx2 is expressed. The AMH1 enhancer is composed of multiple regulatory subregions that share the same spatial specificity. The most active of the regulatory subregions is a 291-bp region that contains at least two Pax2-binding sites, both of which are necessary for the function of the main component (PB1-A region) of the AMH1 enhancer. In accordance with these results, enhancer activity in the PB1-A region, as well as gbx2 expression in r1, was missing in no isthmus mutant embryos that lacked functional pax2a. In addition, we identified an upstream conserved sequence of 227bp that suppresses the enhancer activity of AMH1. Taken together, these findings suggest that gbx2 expression during the somitogenesis stage in zebrafish is regulated by a complex mechanism involving Pax2 as well as activators and suppressors in the regions flanking the gene.
Genes / Markers
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Mutations / Transgenics
Human Disease / Model
Sequence Targeting Reagents
Engineered Foreign Genes