Commitment to the myocardial phenotype

在果蝇中，同源异型盒基因tinman是心脏发育所必需的。在脊椎动物中，一个与tinman相关的同源异型盒基因小家族已经被鉴定，包括组织，它们在心脏发育调控中的确切作用尚不清楚。Nkx 2 -5基因在心脏发生中的作用的实验研究表明了这一点。尽管小鼠中Nkx 2 -5基因的消融导致胚胎由于心脏缺陷而死亡，但胚胎含有分化的表面正常的表面正常的心脏，并且主要可观察到的缺陷是成环形态发生的失败。因此，NK 2 -5的作用与果蝇中的tinman基因的作用并不明显相似。Nkx-25消融的相对较小的后果可以通过具有冗余活性的额外tinman家族基因的存在来解释，但目前候选拯救基因的表征是非常初步的。因此，tinman基因家族在脊椎动物心脏发育中的重要性是一个尚未解决的问题。为了进一步探讨tinman基因在心脏发育中的作用，我们在非洲爪蟾（Xenopus laevis）身上进行了一系列实验。首先，我们已经确定了一个新的成员，在心脏发育的早期表达的tinman家族。第二，我们已经进行了实验，在青蛙胚胎中Nkx 2 -5的显性抑制突变形式的表达导致可检测到的心肌分化的完全消除。我们认为这种效应是通过抑制tinman基因家族多个成员的功能来实现的。该研究的长期目标是了解脊椎动物中与锡人相关的基因调控心脏发育的机制。具体的实验目的如下：1）进一步研究导致心肌基因表达消除的机制。2)利用心肌细胞诱导表达系统来确定发育过程中Nkx 2 -5在心肌分化调节中发挥作用的时间。3）。确定Nkx 2 - 5与加塔-4和SRF的组合是否足以指导心肌基因表达。4)为了确定完整的库，在心肌发育过程中表达的tinman家族成员的tinman家族成员在非洲爪蟾心肌发育过程中表达。

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.