Neural Development Unit, UCL Institute of Child Health, 30 Guilford Street, London WC1N 1EH, UK.
Development. 2011 Nov;138(22):4931-42. doi: 10.1242/dev.066597. Epub 2011 Oct 17.
The Wnt/β-catenin pathway plays an essential role during regionalisation of the vertebrate neural plate and its inhibition in the most anterior neural ectoderm is required for normal forebrain development. Hesx1 is a conserved vertebrate-specific transcription factor that is required for forebrain development in Xenopus, mice and humans. Mouse embryos deficient for Hesx1 exhibit a variable degree of forebrain defects, but the molecular mechanisms underlying these defects are not fully understood. Here, we show that injection of a hesx1 morpholino into a 'sensitised' zygotic headless (tcf3) mutant background leads to severe forebrain and eye defects, suggesting an interaction between Hesx1 and the Wnt pathway during zebrafish forebrain development. Consistent with a requirement for Wnt signalling repression, we highlight a synergistic gene dosage-dependent interaction between Hesx1 and Tcf3, a transcriptional repressor of Wnt target genes, to maintain anterior forebrain identity during mouse embryogenesis. In addition, we reveal that Tcf3 is essential within the neural ectoderm to maintain anterior character and that its interaction with Hesx1 ensures the repression of Wnt targets in the developing forebrain. By employing a conditional loss-of-function approach in mouse, we demonstrate that deletion of β-catenin, and concomitant reduction of Wnt signalling in the developing anterior forebrain of Hesx1-deficient embryos, leads to a significant rescue of the forebrain defects. Finally, transcriptional profiling of anterior forebrain precursors from mouse embryos expressing eGFP from the Hesx1 locus provides molecular evidence supporting a novel function of Hesx1 in mediating repression of Wnt/β-catenin target activation in the developing forebrain.
Wnt/β-catenin 通路在脊椎动物神经板的区域化过程中发挥着重要作用，其在前脑神经外胚层中的抑制作用是正常前脑发育所必需的。Hesx1 是一种保守的脊椎动物特异性转录因子，对于非洲爪蟾、小鼠和人类的前脑发育是必需的。缺乏 Hesx1 的小鼠胚胎表现出不同程度的前脑缺陷，但这些缺陷的分子机制尚不完全清楚。在这里，我们表明，在“敏感”无头（tcf3）突变体背景下注射 hesx1 形态发生素会导致严重的前脑和眼睛缺陷，这表明 Hesx1 和 Wnt 通路在斑马鱼前脑发育过程中存在相互作用。与 Wnt 信号抑制的需求一致，我们强调了 Hesx1 和 Tcf3 之间协同的基因剂量依赖性相互作用，Tcf3 是 Wnt 靶基因的转录抑制剂，在小鼠胚胎发生过程中维持前脑的身份。此外，我们揭示了 Tcf3 在神经外胚层中对于维持前脑特征是必需的，并且它与 Hesx1 的相互作用确保了在发育中的前脑中 Wnt 靶基因的抑制。通过在小鼠中采用条件性缺失功能的方法，我们证明了β-catenin 的缺失以及 Hesx1 缺失胚胎中前脑前部 Wnt 信号的减少，导致前脑缺陷的显著挽救。最后，通过对表达 Hesx1 基因座的 eGFP 的小鼠胚胎前脑前体进行转录谱分析，提供了分子证据，支持 Hesx1 在介导发育中的前脑中 Wnt/β-catenin 靶激活的抑制作用的新功能。
