Craniofacial Defects in the Manta-Ray Line: A Novel Model for Ribosomopathies

描述（由申请人提供）：唇腭裂是最常见的出生缺陷之一，大约每700名活产婴儿中就有一例。虽然可以通过重建手术治疗，但口腔裂会在生命早期引起并发症，从喂养问题到听力和语言缺陷。此外，这些患者中的许多人还表现出精神发育迟滞或其他神经发育问题。在对小鼠进行的正向遗传筛选中，我们发现了一个名为manta-ray（mray）的新品系，它表现出严重的发育缺陷，包括上颌正中裂和继发性腭以及异常的大脑发育。我们确定了Pak 1 ip 1基因的致病性隐性突变，该基因编码核糖体生物合成所需的前核糖体因子。Pak 1 ip 1的缺失激活肿瘤抑制因子和细胞周期控制因子Tp 53，导致细胞周期停滞和细胞死亡。这一途径似乎是核糖体病的许多临床特征，包括其颅面异常的关键介质。我们目前对Pak 1 ip 1功能的理解强烈支持这样的假设，即纯合mray突变体中Pak 1 ip 1缺陷激活了TP 53通路，并导致TP 53介导的颅神经嵴细胞丢失，从而导致中线分裂。我们在此提出的实验，将通过对神经上皮细胞死亡、增殖和神经嵴衍生组织的特化的详细分析，揭示引起纯合子mray突变体颅面畸形的机制。在 在第二组实验中，我们将尝试通过药理学或遗传学手段抑制Tp 53反应来改善或甚至挽救受影响突变体中的中线裂缝。最后，我们将研究mray突变影响核糖体生物合成过程的方式，特别是通过分析中面特异性 生长因子总之，我们的研究将为核糖体生物合成缺陷导致颅面出生缺陷的机制提供实质性的新见解，这是常见的和临床上重要的，并将通过干扰TP 53途径探索治疗方案。

DESCRIPTION (provided by applicant): Clefts of lip and palate are among the most common birth defects, occurring in approximately every 700 live births. Although treatable by reconstructive surgery, oral clefts cause complications early in life ranging from feeding problems to hearing and speech defects. In addition, many of these patients also show mental retardation or other neurodevelopmental problems. In a forward genetic screen carried out in mice we recovered a novel line named manta-ray (mray), which displays severe developmental defects including a median cleft of the upper jaw and secondary palate as well as abnormal brain development. We identified the causative recessive mutation in the Pak1ip1 gene, which encodes a preribosomal factor required for ribosome biogenesis. Loss of Pak1ip1 activates the tumor suppressor and cell cycle control factor Tp53, which leads to cell cycle arrest and cell death. This pathway appears to be a critical mediator of many of the clinical features of ribosomopathies including their craniofacial anomalies. Our current understanding of Pak1ip1 function strongly supports the hypothesis that Pak1ip1- deficiency in homozygous mray mutants activates the Tp53 pathway and leads to Tp53-mediated loss of cranial neural crest cells, which results in midline clefting. The experiments we propose here, will uncover the mechanisms that cause the craniofacial anomalies of homozygous mray mutants by providing a detailed analysis of neuroepithelial cell death, proliferation, and specification of neural crest-derived tissues. In second set of experiments, we will attempt to ameliorate or even rescue the midline cleft in affected mutants by inhibiting Tp53 response either through pharmacological or genetic means. Finally, we will examine the way the mray mutation affects the process of ribosome biogenesis in general and in particular, by analyzing specific deficits in the translation of midface-specific growth factors. In summary, our study will provide substantial new insight into the mechanisms by which defects in ribosome biogenesis can lead to craniofacial birth defects, which are common and clinically important and will explore treatment options by interfering with the Tp53 pathway.