Commitment to the myocardial phenotype

在果蝇中，同源框基因tinman对于心脏的发育是绝对必要的。在脊椎动物中，已经发现了一个与锡曼相关的同源盒基因小家族，包括组织，它们在心脏发育调节中的确切作用尚不清楚。研究人员对Nkx2-5基因在心脏发生中的作用的实验表明了这一点。尽管去除Nkx2-5基因会导致小鼠胚胎因心脏缺陷而死亡，但胚胎包含一个分化的表面正常、表面正常的心脏，主要可观察到的缺陷是环状形态发生失败。因此，Nk2-5在果蝇中的作用与锡曼基因没有明显的相似之处。Nkx-25消融的后果相对较小，可以通过存在额外的具有多余活性的Tinman家族基因来解释，但目前对候选拯救基因的表征非常初步。因此，Tinman基因家族对脊椎动物心脏发育的重要性目前是一个悬而未决的问题。为了进一步探索锡曼基因在心脏发育中的作用，我们在非洲爪蛙身上进行了一系列实验。首先，我们已经确定了Tinman家族中一个新的成员，该成员在心脏发育早期表达。其次，我们进行了在青蛙胚胎中表达显性抑制突变形式的Nkx2-5导致完全消除可检测到的心肌分化的实验。我们提出，这种作用是通过抑制锡曼基因家族的多个成员的功能来实现的。这项拟议研究的长期目标是了解脊椎动物锡曼相关基因调节心脏发育的机制。具体的实验目的如下：-1)进一步研究心肌基因表达缺失的机制。2)利用激素诱导表达系统确定Nkx2-5在发育过程中对心肌分化的调节作用时间。3)。确定Nkx2-5联合GATA-4和SRF是否足以指导心肌基因的表达。4)确定非洲爪哇Tinman家族成员在心肌发育过程中表达的完整谱带。

In Drosophila, the homeobox gene tinman is absolutely required for development of the heart. In vertebrates, a small family of homeobox genes that are related to tinman have been identified, including tissues, their precise role in regulation of cardiac development remains unclear. This is illustrated by experiments investigators the role of the Nkx2-5 gene in cardiogenesis. Although, ablation of the Nkx2-5 gene in mouse results in embryonic death due to heart defects, the embryos contain a differentiated superficially normal , superficially normal heart and the major observable defect is a failure of looping morphogenesis. The role of Nk2-5 therefore, is not obviously similar to that of the tinman gene in the fly. The relatively minor consequences of Nkx-25 ablation, could be explained by the presence of additional tinman family genes with redundant activities, but at present the characterization of candidate rescuing genes is very preliminary. Therefore, the importance of the tinman gene family for vertebrate heart development is currently an unresolved question. In order to further explore the role of the tinman genes during heart development, we have carried out a series of experiments in the frog, Xenopus laevis. First, we have identified a novel member of the tinman family that is expressed early during heart development. Second we have carried out experiments in which expression of a dominant inhibitory mutant form of Nkx2-5 in the frog embryos results in total elimination of detectable myocardial differentiation. We proposed that this effect is achieved by inhibition of the function of multiple members of the tinman gene family. The long term objective of the proposed research is to understand the mechanism by which the vertebrate tinman-related genes regulate cardiac development. The specific experimental aims are as follows: -1) to further examine the mechanism leading to the elimination of myocardial gene expression. 2) to use a hormone-inducible expression systems to determine the time during development that Nkx2-5 plays its role in regulation of myocardial differentiation. 3). To determine whether Nkx2- 5, in combination with GATA-4 and SRF is sufficient to direct myocardial gene expression. 4) To identify the complete repertoire of tinman family members expressed during myocardial development of tinman family members expressed during myocardial development in Xenopus.