Dual hindlimb control elements in the Tbx4 gene and region-specific control of bone size in vertebrate limbs
Dual hindlimb control elements in the Tbx4 gene and region-specific control of bone size in vertebrate limbs
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DOI：
10.1242/dev.017384
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发表时间：
2008-08-01
期刊：
影响因子：
4.6
通讯作者：
Kingsley, David M.
中科院分区：
文献类型：
--
作者：
Menke, Douglas B.;Guenther, Catherine;Kingsley, David M.
Tbx4转录因子对正常后肢和血管发育至关重要，但对其高度保守的表达模式是如何产生的知之甚少。我们已经使用比较基因组学和功能扫描在转基因小鼠中，以确定一个分散组的增强控制Tbx4在不同组织中的表达。两个独立的增强子控制后肢表达，一个位于Tbx4编码外显子的上游，一个位于Tbx4编码外显子的下游。这两种增强子，后肢增强子A和后肢增强子B（HLEA和HLE B），在它们的一级序列、它们在后肢内的精确活性模式以及它们在动物间的序列保守程度上不同。HLEB从鱼类到哺乳动物高度保守。尽管Tbx4表达和后肢发育在鱼和哺乳动物中发生在不同的轴向水平，但从鱼或小鼠克隆的HLEB能够在小鼠胚胎中后肢发育的适当位置驱动表达。HLEA仅在哺乳动物中高度保守。从内源性小鼠基因座中删除HLEA减少了胚胎发生期间后肢中Tbx4的表达，绕过了Tbx4无效突变的胚胎致死性，并产生了可存活的、可生育的小鼠，其后肢而非前肢的骨骼大小发生了特征性变化。我们推测，双后肢增强子提供了一个灵活的基因组机制，在正常发育过程中改变Tbx4表达的强度和位置，使得有可能分别修改的大小前肢和后肢骨脊椎动物进化过程中。发展
The Tbx4 transcription factor is crucial for normal hindlimb and vascular development, yet little is known about how its highly conserved expression patterns are generated. We have used comparative genomics and functional scanning in transgenic mice to identify a dispersed group of enhancers controlling Tbx4 expression in different tissues. Two independent enhancers control hindlimb expression, one located upstream and one downstream of the Tbx4 coding exons. These two enhancers, hindlimb enhancer A and hindlimb enhancer B ( HLEA and HLEB), differ in their primary sequence, in their precise patterns of activity within the hindlimb, and in their degree of sequence conservation across animals. HLEB is highly conserved from fish to mammals. Although Tbx4 expression and hindlimb development occur at different axial levels in fish and mammals, HLEB cloned from either fish or mouse is capable of driving expression at the appropriate position of hindlimb development in mouse embryos. HLEA is highly conserved only in mammals. Deletion of HLEA from the endogenous mouse locus reduces expression of Tbx4 in the hindlimb during embryogenesis, bypasses the embryonic lethality of Tbx4-null mutations, and produces viable, fertile mice with characteristic changes in the size of bones in the hindlimb but not the forelimb. We speculate that dual hindlimb enhancers provide a flexible genomic mechanism for altering the strength and location of Tbx4 expression during normal development, making it possible to separately modify the size of forelimb and hindlimb bones during vertebrate evolution. DEVELOPMENT