Cross-regulation in the mouse HoxB complex: the expression of Hoxb2 in rhombomere 4 is regulated by Hoxb1
Cross-regulation in the mouse HoxB complex: the expression of Hoxb2 in rhombomere 4 is regulated by Hoxb1
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DOI：
10.1101/gad.11.14.1885
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发表时间：
1997-07-15
影响因子：
10.5
通讯作者：
Krumlauf, R
中科院分区：
文献类型：
--
作者：
Maconochie, MK;Nonchev, S;Krumlauf, R
Hox基因表达的片段限制模式的正确调节对于脊椎动物后脑的正确模式化是必不可少的。我们已经研究了限制性表达的Hoxb 2的菱形4（R4）的分子基础，通过使用在转基因小鼠中的缺失分析，以确定从小鼠基因的R4增强子。一个二分的Hox/Pbx结合基序位于该增强子内，体外DNA结合实验表明，脊椎动物唇相关蛋白Hoxb 1将以Pbx/Exd依赖的方式协同结合到该位点。Hoxb 2 r4增强子可以通过转基因小鼠中Hoxb 1、Hoxa 1和果蝇唇的异位表达在体内被反式激活。相比之下，异位Hoxb 2和Hoxb 4无法诱导表达，这表明在体内该增强子优先响应阴唇家族成员。突变分析表明，二分的Hox/Pbx基序是必需的r4增强子活性和类维生素A和异位Hox表达的反应。此外，Hoxb 2基序的三个拷贝足以介导转基因小鼠胚胎中的r4表达和果蝇胚胎中的唇图案。果蝇胚胎中的报告基因表达依赖于内源性唇和exd，这表明Hox/Pbx位点与唇相关蛋白相互作用的能力在进化上是保守的。内源性Hoxb 2基因在Hoxb 1纯合突变胚胎中的r4中不再上调。在这些实验的基础上，我们得出结论，在后脑Hoxb 2的R4-限制性结构域是由Hoxb 1涉及脊椎动物Pbx蛋白作为辅因子的直接交叉调节相互作用的结果。这表明Hoxb 1在维持r4身份中的部分功能作用可能是由Hoxb 2基因介导的。
Correct regulation of the segment-restricted patterns of Hox gene expression is essential for proper patterning of the vertebrate hindbrain. We have examined the molecular basis of restricted expression of Hoxb2 in rhombomere 4 (r4), by using deletion analysis in transgenic mice to identify an r4 enhancer from the mouse gene. A bipartite Hox/Pbx binding motif is located within this enhancer, and in vitro DNA binding experiments showed that the vertebrate labial-related protein Hoxb1 will cooperatively bind to this site in a Pbx/Exd-dependent manner. The Hoxb2 r4 enhancer can be transactivated in vivo by the ectopic expression of Hoxb1, Hoxa1, and Drosophila labial in transgenic mice. In contrast, ectopic Hoxb2 and Hoxb4 are unable to induce expression, indicating that in vivo this enhancer preferentially responds to labial family members. Mutational analysis demonstrated that the bipartite Hox/Pbx motif is required for r4 enhancer activity and the responses to retinoids and ectopic Hox expression. Furthermore, three copies of the Hoxb2 motif are sufficient to mediate r4 expression in transgenic mouse embryos and a labial pattern in Drosophila embryos. This reporter expression in Drosophila embryos is dependent upon endogenous labial and exd, suggesting that the ability of this Hox/Pbx site to interact with labial-related proteins has been evolutionarily conserved. The endogenous Hoxb2 gene is no longer upregulated in r4 in Hoxb1 homozygous mutant embryos. On the basis of these experiments we conclude that the r4-restricted domain of Hoxb2 in the hindbrain is the result of a direct cross-regulatory interaction by Hoxb1 involving vertebrate Pbx proteins as cofactors. This suggests that part of the functional role of Hoxb1 in maintaining r4 identity may be mediated by the Hoxb2 gene.