Genetic analysis of a spontaneous mutation in a rat with a novel hind limb defect

描述(申请人提供)：我们在这里描述了一个新的大鼠突变，它是由两只SpragueDawley大鼠在一个群体中交配而自发产生的，我们维持这个群体是为了研究另一个突变Nuc1。Nuc1是一种眼睛特异的表型，具有发育异常，我们已经研究了几年。新突变动物的后肢伸展和被绑架得如此严重，以至于无法有效地支撑动物的体重。由于这种不同寻常的外表和步态异常，我们将突变株命名为弗罗格腿。与正常胎鼠相比，福罗格腿鼠的大脑在大小和重量上都较小；然而，受影响的新生大鼠的体重通常较低，几个月后确实恢复到正常水平。福氏坐骨神经组织学分析显示雪旺细胞有异常改变。神经计量学研究还表明，FRogleg大鼠的坐骨神经复合肌肉动作电位显著降低。试图让弗罗格利格动物彼此交配或与表型正常的雄性和雌性交配，但都没有成功。携带该品系因缺乏杂合子表型而变得复杂。我们能够通过随机组合饲养未受影响的一窝弗罗格大鼠，直到特定的交配产生弗罗格后代，从而确定父母为杂合子，从而使弗罗格品系永久化。我们已经确定这种情况是以孟德尔方式遗传的，是一种单一的常染色体隐性性状，并使用遗传连锁分析将该基因定位到大鼠染色体1q36-37。这一发病间隔已缩小到2.7MBP的染色体区域。基于最新的大鼠基因组组装的参考序列注释数据库，有8个潜在的Fogue Leg基因候选。然而，通过与人类和小鼠基因组的同线部分对齐来增加这一数量，使该区间内的基因总数增加到大约19个。在当前的应用中，我们试图确定导致Fogue Leg表型的基因和特定的突变。此外，我们还将更好地描述福格列格大鼠的神经异常。了解基因的特性和突变的性质将有助于我们进一步了解导致这种有趣表型的分子和细胞机制。我们的工作假设是，该突变和导致Fogue Leg表型的基因的鉴定将为研究神经发育障碍的细胞和分子机制提供一个新的模型。因此，我们提出了以下目标：具体目标1：完善Fogue Leg基因座的连锁图谱。特异性目的2：鉴定Fogue Leg基因及其突变。特异目的3：研究福罗格列鼠表型的病理基础。识别与Fogue腿有关的基因将是朝着确定该模型在研究神经发育障碍机制方面的潜在价值迈出的重要一步。 与公共卫生相关：弗罗格鼠是一种新的自发突变，具有明确的后肢残疾。这种缺陷源于神经系统。随着该基因的鉴定和特异性突变的出现，福罗格鼠将成为研究神经发育障碍的一种有价值的动物模型。

DESCRIPTION (provided by applicant): We describe here a novel rat mutant that arose spontaneously from a mating of two Sprague Dawley rats in a colony that we maintain to study another mutation, Nuc1. Nuc1 is an eye-specific phenotype with developmental abnormalities that we have been investigating for several years. Hind limbs of the new mutant animals are extended and abducted so severely that they do not effectively support the animal's weight. Because of this unusual appearance and gait anomaly, we have named the mutant strain frogleg. The brain of a frogleg rat is smaller in size and weight relative to normal littermates; however body weight, which is typically lower in the affected newborn rats, does catch up to normal after several months. Histological analysis of frogleg sciatic nerve revealed some abnormal changes in Schwann cells. Neurometric studies also showed that sciatic compound muscle action potential is significantly reduced in frogleg rats. Attempts to breed frogleg animals with each other or with phenotypically normal males and females were unsuccessful. Carrying the line was complicated by the absence of a heterozygote phenotype. We were able to perpetuate the frogleg line by breeding unaffected littermates of frogleg rats in random combination until specific matings produced frogleg progeny, thereby identifying the parents as heterozygotes. We have established that the condition is inherited in a Mendelian fashion as a single autosomal recessive trait, and have used genetic linkage analysis to map the gene to rat chromosome 1q36-37. This disease interval has been reduced to a chromosomal region of 2.7 Mbp. Based on the Reference Sequence annotation database for the most current rat genome assembly, there are 8 potential frogleg gene candidates. However, augmentation of this number by alignment with syntenic portions of the human and mouse genomes increases the total number of genes in the interval to approximately 19. In the current application, we seek to identify the gene and the specific mutation responsible for the frogleg phenotype. In addition we will better characterize the neurological abnormalities of frogleg rats. Knowing the gene's identity and the nature of the mutation will help us to further understand the molecular and cellular mechanisms responsible for this interesting phenotype. Our working hypothesis is that identification of the mutation and the gene responsible for the frogleg phenotype will provide a novel model for studying cellular and molecular mechanisms of neurodevelopmental disorders. Therefore, we propose the following aims: SPECIFIC AIM 1: To refine the linkage map of the frogleg locus. SPECIFIC AIM 2: To identify the frogleg gene and mutation. SPECIFIC AIM 3: To characterize the pathology that underlies the phenotype of the frogleg rat. The identification of the gene responsible for frogleg would be a major step toward defining the potential value of the model for the study of mechanisms involved in neurodevelopmental disorders. PUBLIC HEALTH RELEVANCE: The frogleg rat is a novel spontaneous mutant with a well-defined hind limb disability. This defect is neurological in origin. With the identification of the gene and specific mutation, the frogleg rat will become a valuable animal model for the study of neurodevelopmental disorders.