Lens induction is a classical developmental model allowing investigation of cell specification, spatiotemporal control of gene expression, as well as how transcription factors are integrated into highly complex gene regulatory networks (GRNs). Pax6 represents a key node in the gene regulatory network governing mammalian lens induction. Meis1 and Meis2 homeoproteins are considered as essential upstream regulators of Pax6 during lens morphogenesis based on their interaction with the ectoderm enhancer (EE) located upstream of Pax6 transcription start site. Despite this generally accepted regulatory pathway, Meis1-, Meis2- and EE-deficient mice have surprisingly mild eye phenotypes at placodal stage of lens development. Here, we show that simultaneous deletion of Meis1 and Meis2 in presumptive lens ectoderm results in arrested lens development in the pre-placodal stage, and neither lens placode nor lens is formed. We found that in the presumptive lens ectoderm of Meis1/Meis2 deficient embryos Pax6 expression is absent. We demonstrate using chromatin immunoprecipitation (ChIP) that in addition to EE, Meis homeoproteins bind to a remote, ultraconserved SIMO enhancer of Pax6. We further show, using in vivo gene reporter analyses, that the lens-specific activity of SIMO enhancer is dependent on the presence of three Meis binding sites, phylogenetically conserved from man to zebrafish. Genetic ablation of EE and SIMO enhancers demostrates their requirement for lens induction and uncovers an apparent redundancy at early stages of lens development. These findings identify a genetic requirement for Meis1 and Meis2 during the early steps of mammalian eye development. Moreover, they reveal an apparent robustness in the gene regulatory mechanism whereby two independent "shadow enhancers" maintain critical levels of a dosage-sensitive gene, Pax6, during lens induction.
- MeSH
- dánio pruhované genetika MeSH
- ektoderm růst a vývoj patologie MeSH
- genové regulační sítě genetika MeSH
- homeodoménové proteiny genetika metabolismus MeSH
- lidé MeSH
- myši MeSH
- nádorové proteiny genetika metabolismus MeSH
- oči růst a vývoj metabolismus patologie MeSH
- oční čočka růst a vývoj metabolismus patologie MeSH
- transkripční faktor PAX6 genetika metabolismus MeSH
- vazebná místa MeSH
- vývojová regulace genové exprese MeSH
- zesilovače transkripce genetika MeSH
- zvířata MeSH
- Check Tag
- lidé MeSH
- myši MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
The Wnt/β-catenin signaling pathway controls many processes during development, including cell proliferation, cell differentiation and tissue homeostasis, and its aberrant regulation has been linked to various pathologies. In this study we investigated the effect of ectopic activation of Wnt/β-catenin signaling during lens fiber cell differentiation. To activate Wnt/β-catenin signaling in lens fiber cells, the transgenic mouse referred to as αA-CLEF was generated, in which the transactivation domain of β-catenin was fused to the DNA-binding protein LEF1, and expression of the transgene was controlled by αA-crystallin promoter. Constitutive activation of Wnt/β-catenin signaling in lens fiber cells of αA-CLEF mice resulted in abnormal and delayed fiber cell differentiation. Moreover, adult αA-CLEF mice developed cataract, microphthalmia and manifested downregulated levels of γ-crystallins in lenses. We provide evidence of aberrant expression of cell cycle regulators in embryonic lenses of αA-CLEF transgenic mice resulting in the delay in cell cycle exit and in the shift of fiber cell differentiation to the central fiber cell compartment. Our results indicate that precise regulation of the Wnt/β-catenin signaling activity during later stages of lens development is essential for proper lens fiber cell differentiation and lens transparency.
- MeSH
- beta-katenin genetika metabolismus MeSH
- buněčná diferenciace genetika MeSH
- buněčný cyklus genetika MeSH
- DNA vazebné proteiny genetika metabolismus MeSH
- epitelové buňky metabolismus MeSH
- katarakta genetika metabolismus MeSH
- krystaliny genetika metabolismus MeSH
- lidé MeSH
- mikroftalmie genetika metabolismus MeSH
- myši inbrední C57BL MeSH
- myši transgenní genetika metabolismus MeSH
- myši MeSH
- oční čočka metabolismus MeSH
- promotorové oblasti (genetika) genetika MeSH
- signální dráha Wnt genetika MeSH
- signální transdukce genetika MeSH
- transkripční faktor LEF-1 MeSH
- vývojová regulace genové exprese MeSH
- zvířata MeSH
- Check Tag
- lidé MeSH
- mužské pohlaví MeSH
- myši MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- MeSH
- finanční podpora výzkumu jako téma MeSH
- Publikační typ
- abstrakty MeSH
