Li X, Wikramanayake A H, Klein W H
Department of Biochemistry and Molecular Biology, University of Texas M. D. Anderson Cancer Center, Houston, Texas, 77030, USA.
Dev Biol. 1999 Aug 15;212(2):425-39. doi: 10.1006/dbio.1999.9360.
We show here that the homeodomain transcription factor SpOtx is required for endoderm and aboral ectoderm formation during sea urchin embryogenesis. SpOtx target genes were repressed by fusing the SpOtx homeodomain to an active repression domain of Drosophila Engrailed. The Engrailed-SpOtx fusion protein reduced the expression of endoderm- and aboral ectoderm-specific genes and inhibited the formation of endoderm and aboral ectoderm cell types. Coexpressing activated beta-catenin with Engrailed-SpOtx did not overcome the inhibition of endoderm and aboral ectoderm formation, suggesting that SpOtx functioned either downstream of or parallel to nuclear beta-catenin. Embryos expressing C-cadherin, which blocks nuclear translocation of beta-catenin, have defects in endoderm and aboral ectoderm formation. Coexpressing SpOtx with C-cadherin restored aboral ectoderm-specific gene expression and aboral ectoderm morphology, but with C-cadherin present, SpOtx was not sufficient for endoderm formation. Our results show that SpOtx plays a key role in the activation of aboral ectoderm- and endoderm-specific gene expression and, in addition, suggest that SpOtx mediates some of beta-catenin's functions in endoderm and aboral ectoderm formation.
我们在此表明，同源异型域转录因子SpOtx是海胆胚胎发育过程中内胚层和反口外胚层形成所必需的。通过将SpOtx同源异型域与果蝇Engrailed的活性抑制结构域融合，抑制了SpOtx靶基因。Engrailed-SpOtx融合蛋白降低了内胚层和反口外胚层特异性基因的表达，并抑制了内胚层和反口外胚层细胞类型的形成。将活化的β-连环蛋白与Engrailed-SpOtx共表达并不能克服对内胚层和反口外胚层形成的抑制作用，这表明SpOtx在核β-连环蛋白的下游发挥作用或与之平行发挥作用。表达C-钙黏蛋白（其可阻止β-连环蛋白的核转位）的胚胎在内胚层和反口外胚层形成方面存在缺陷。将SpOtx与C-钙黏蛋白共表达可恢复反口外胚层特异性基因的表达和反口外胚层形态，但在存在C-钙黏蛋白的情况下，SpOtx不足以促进内胚层的形成。我们的结果表明，SpOtx在反口外胚层和内胚层特异性基因表达的激活中起关键作用，此外，还表明SpOtx在内胚层和反口外胚层形成过程中介导了β-连环蛋白的一些功能。
