Department of Biology, Indiana University, Bloomington, IN 47405, USA.
Dev Biol. 2011 Dec 15;360(2):391-402. doi: 10.1016/j.ydbio.2011.09.030. Epub 2011 Oct 8.
In the Drosophila eye the retinal determination (RD) network controls both tissue specification and cell proliferation. Mutations in network members result in severe reductions in the size of the eye primordium and the transformation of the eye field into head cuticle. The zinc-finger transcription factor Teashirt (Tsh) plays a role in promoting cell proliferation in the anterior most portions of the eye field as well as in inducing ectopic eye formation in forced expression assays. Tiptop (Tio) is a recently discovered paralog of Tsh. It is distributed in an identical pattern to Tsh within the retina and can also promote ectopic eye development. In a previous study we demonstrated that Tio can induce ectopic eye formation in a broader range of cell populations than Tsh and is also a more potent inducer of cell proliferation. Here we have focused on understanding the molecular and biochemical basis that underlies these differences. The two paralogs are structurally similar but differ in one significant aspect: Tsh contains three zinc finger motifs while Tio has four such domains. We used a series of deletion and chimeric proteins to identify the zinc finger domains that are selectively used for either promoting cell proliferation or inducing eye formation. Our results indicate that for both proteins the second zinc finger is essential to the proper functioning of the protein while the remaining zinc finger domains appear to contribute but are not absolutely required. Interestingly, these domains antagonize each other to balance the overall activity of the protein. This appears to be a novel internal mechanism for regulating the activity of a transcription factor. We also demonstrate that both Tsh and Tio bind to C-terminal Binding Protein (CtBP) and that this interaction is important for promoting both cell proliferation and eye development. And finally we report that the physical interaction that has been described for Tsh and Homothorax (Hth) do not occur through the zinc finger domains.
在果蝇眼中，视网膜决定（RD）网络控制着组织特化和细胞增殖。网络成员的突变会导致眼原基大小严重减小，并将眼域转化为头部表皮。锌指转录因子 Tea 衣（Tsh）在促进眼域最前部的细胞增殖以及在强制表达分析中诱导异位眼形成方面发挥作用。Tiptop（Tio）是 Tsh 的最近发现的同源物。它在视网膜中的分布与 Tsh 相同，也可以促进异位眼发育。在之前的研究中，我们证明了 Tio 可以在比 Tsh 更广泛的细胞群体中诱导异位眼形成，并且也是更有效的细胞增殖诱导剂。在这里，我们专注于理解这些差异的分子和生化基础。这两个同源物在结构上相似，但在一个重要方面存在差异：Tsh 包含三个锌指基序，而 Tio 有四个这样的结构域。我们使用一系列缺失和嵌合蛋白来鉴定选择性促进细胞增殖或诱导眼形成的锌指结构域。我们的结果表明，对于这两种蛋白质，第二个锌指对于蛋白质的正常功能是必需的，而其余的锌指结构域似乎有贡献，但不是绝对必需的。有趣的是，这些结构域相互拮抗，以平衡蛋白质的整体活性。这似乎是一种调节转录因子活性的新的内部机制。我们还证明 Tsh 和 Tio 都与 C 端结合蛋白（CtBP）结合，并且这种相互作用对于促进细胞增殖和眼发育都很重要。最后，我们报告了已描述的 Tsh 和 Homothorax（Hth）之间的物理相互作用不会通过锌指结构域发生。
