Role of Bop in Cardiac Development and Function

说明（由申请人提供）：先天性心脏病和获得性心脏病分别是儿童和成人的主要非传染性死亡原因。该项目的长期目标是了解m-Bop蛋白在心肌细胞分化和心脏发育中的作用。Bop编码的m-Bop蛋白在发育早期的小鼠和鸡的心田和肌组以及胎儿和成年小鼠的心肌和骨骼肌中特异性表达。m-Bop蛋白包含MYND结构域和S-ET结构域，前者用于募集组蛋白去乙酰化酶（hdac），后者用于影响染色质结构，有时通过内在组蛋白甲基转移酶（HMT）活性。这两种活性都可以通过涉及染色质修饰的表观遗传效应抑制基因表达。Bop在小鼠体内的靶向失活可导致胚胎第10天（El0）死亡，Bop缺失的胎儿心脏缺少右心室，心肌细胞分化异常。e775 bop缺失胚胎的心脏原基中缺少转录因子Hand2，这表明m-Bop在导致右心室发育的早期基因级联表达中起作用。m-Bop在体外因募集hdac而具有抑制活性，并与hdac直接或间接发生物理相互作用。m-Bop与skNAC（一种心脏和骨骼肌特异性转录因子）相互作用，并在体外和体内心肌形成过程中与skNAC共定位。m-Bop还与MITR（一种肌肉生成的共同抑制因子）和HRT2（一种心脏心室特异性转录因子）相互作用。我们计划验证以下假设：1)m-Bop是心肌细胞发育早期染色质修饰的心脏特异性调节剂，并通过与dna结合蛋白的直接和间接相互作用发挥功能；2)m-Bop和skNAC在体外肌肉形成和体内心脏发育过程中以生理上有意义的方式相互作用。具体目的是：1)明确m-Bop的MYND、SET和其他结构域促进染色质结构改变和调控转录的机制；2)确定m-Bop/skNAC相互作用的生物学意义以及skNAC在心脏发生中的作用。这些研究可能与先天性心脏病脑室发育不全的机制有关。m-Bop似乎通过促进组蛋白修饰，从而以一种谱系特异性的方式重组染色质，从而特异性地影响心脏发育，这使它成为少数已知以这种方式运作的蛋白质之一。这使得拟议研究中要调查的机制具有更广泛的相关性。

DESCRIPTION (provided by applicant): Congenital heart disease and acquired heart disease are the leading non-infectious causes of death in children and adults, respectively. The long term objectives of this project are to understand the role of m-Bop proteins in cardiac myocyte differentiation and cardiac development. Bop encodes m-Bop proteins specifically expressed in the heart field and myotome of the mouse and chick early in development as well as in fetal and adult mouse myocardium and skeletal muscle. m-Bop proteins contain both a MYND domain, shown in other proteins to recruit histone deacetylases (HDACs), and a S-ET domain, shown elsewhere to affect chromatin structure, sometimes through intrinsic histone methyltransferase (HMT) activity. Both activities can repress gene expression through epigenetic effects involving chromatin modifications. Targeted inactivation of Bop in mice leads to death at embryonic day 10 (El0 0), and hearts of Bop-null fetuses lack a right ventricle and have abnormal cardiomyocyte differentiation. Absence of the transcription factor, Hand2, from the heart primordia of E7 75 Bop-null embryos suggests a role for m-Bop in an early gene expression cascade that leads to right ventricular development. m-Bop has repressive activity in vitro due to recruitment of HDACs, and it physically interacts directly or indirectly with HDACs. m-Bop interacts with skNAC, a heart- and skeletal muscle-specific transcription factor, and co-localizes with skNAC during myogenesis in vitro and during cardiogenesis in vivo. m-Bop also interacts with MITR, a co-repressor of myogenesis, and HRT2, a heart ventricle-specific transcription factor. We plan to test the hypotheses that 1) m-Bop is a cardiac-specific regulator of chromatin modifications early in cardiomyocyte development and functions through direct and indirect interactions with DNA-binding proteins, and 2) that m-Bop and skNAC interact in a physiologically meaningful manner during myogenesis in vitro and cardiac development in vivo. Specific Aims are 1) To define the mechanisms by which the MYND, SET and other domains of m-Bop promote alterations in chromatin structure and regulate transcription, and 2) To determine the biological significance of m-Bop/skNAC interaction and the role of skNAC during cardiogenesis. These studies are relevant to mechanisms that may underlie ventricular hypoplasia in congenital heart disease. That m-Bop appears to specifically affect heart development by promoting histone modifications and hence chromatin reorganization in a lineage-specific fashion places it among a very few proteins known to operate in this way. This gives a broader relevance to the mechanisms to be investigated in the proposed studies.