Xom Proteolysis During Early Vertebrate Embryogenesis

描述(由申请人提供)： 泛素介导的蛋白分解在早期胚胎发育的信号转导中起着重要的作用。早期发育途径蛋白分解的失调常常导致成年后肿瘤的形成。因此，探索早期胚胎发生中的蛋白分解为揭示与肿瘤发生相关的机制提供了一个独特的机会。在我的K08奖所涵盖的调查中，我们发现XOM，BMP4信号通路的同源盒转录因子，在原肠形成开始时以一种阶段特异性的方式降解。我们已经确定了XOM的破坏基序和破坏基序的关键潜在磷酸化位点(Ser140和Ser144)，这对XOM的稳定性是重要的。我们进一步证明，SCF-β-TRCP很可能是参与XOM降解的细胞内E3泛素连接酶。在非洲爪哇早期胚胎发生过程中，非降解XOM的表达干扰了背腹模式的形成，这表明了蛋白分解在早期胚胎发生中的重要性。两个重要的问题仍然存在：1)XOM在原肠前期是如何稳定的，2)是什么在原肠形成开始时启动了XOM的蛋白分解。根据我们的初步研究，我们假设XOM破坏基序的磷酸化在决定XOM早期发育的稳定性方面起着调节作用，丝氨酸/苏氨酸激酶在原肠形成开始时磷酸化XOM并触发XOM降解。我们建议解决以下具体目标来检验这一假设： 1)明确(Ser140/144)磷酸化在XOM体外降解中的作用； 2)确定(Ser140/144)磷酸化在体内XOM降解中的潜在调节作用； 3)鉴定在早期胚胎发育中使XOM的Ser140/144磷酸化的蛋白。 这些问题的答案将为同源异型盒功能的稳定性如何在发育过程中受到调控提供证据，这不仅对于理解胚胎发生的基本机制，而且对于理解广泛的疾病，如肿瘤的发病机制，都具有重要的意义。

DESCRIPTION (provided by applicant): Ubiquitin-mediated proteolysis plays important roles in governing signaling during early embryogenesis. Dysregulation of proteolysis of early developmental pathways often results in tumor formation in adult life. Exploring proteolysis during early embryogenesis, therefore, offers a unique opportunity to unveil mechanisms pertinent to tumorigenesis. During the investigation covered by my K08 award, we found that Xom, a homeobox transcriptional factor of the BMP4 signaling pathway, was degraded in a stage-specific manner at the onset of gastrulation. We have identified the destruction motif of Xom and the critical potential phosphorylation sites (Ser140 and Ser144) of the destruction motif that are important for Xom stability. We have further shown that the SCF-beta-TRCP is most likely the cellular E3 ubiquitin ligase involved in Xom degradation. Expression of non-degradable Xom disrupts dorsoventral pattern formation during early Xenopus embryogenesis, indicating the importance of regulated proteolysis during early embryogenesis. Two important questions remains: 1) how is Xom stabilized during pre-gastrulation phase and 2) what turns on Xom proteolysis at the onset of gastrulation. Based on our preliminary studies, we hypothesized that phosphorylation of the Xom destruction motif plays a regulatory role in determining Xom stability during early development, and a serine/threonine kinase phosphorylates Xom at the onset of gastrulation and triggers Xom degradation. We propose to address the following specific aims to test this hypothesis: 1) Define the function of (Ser140/144) phosphorylation in Xom degradation in vitro; 2) Determine a potential regulatory role of (Ser140/144) phosphorylation in Xom degradation in vivo; 3) Identify the kinase that phosphorylates Ser140/144 of Xom during early embryogenesis. Answers to these questions will present the evidence of how stability of homeobox function is regulated developmentally, which will bear great implications for understanding not only the basic mechanism of embryogenesis but also a broad spectrum of diseases, such as pathogenesis of neoplasm.