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

描述（由申请人提供）：我们在此描述了一种新的大鼠突变体，该突变体自发产生于一个群体中两只Sprague道利大鼠的交配，我们维持该群体以研究另一种突变Nuc 1。Nuc 1是一种具有发育异常的眼特异性表型，我们已经研究了几年。新突变动物的后肢被严重地伸展和外展，以至于它们不能有效地支撑动物的体重。由于这种不寻常的外观和步态异常，我们命名为突变株蛙腿。蛙腿鼠的大脑相对于正常的同窝出生的大鼠在尺寸和重量上较小;然而，体重在受影响的新生大鼠中通常较低，在几个月后确实赶上正常。蛙腿坐骨神经的组织学分析显示许旺细胞有一些异常变化。神经测量学研究也显示蛙腿大鼠坐骨神经复合肌动作电位显著降低。试图繁殖蛙腿动物彼此或与表型正常的男性和女性是不成功的。携带该品系由于缺乏杂合子表型而变得复杂。我们能够通过随机组合繁殖未受影响的蛙腿大鼠的同窝仔，直到特定的交配产生蛙腿后代，从而将父母鉴定为杂合子，从而使蛙腿品系永久化。我们已经确定，这种情况是遗传在孟德尔的方式作为一个单一的常染色体隐性性状，并已使用遗传连锁分析，以地图的基因到大鼠染色体1 q36 -37。这种疾病的间隔已减少到2.7 Mbp的染色体区域。基于最新大鼠基因组组装的参考序列注释数据库，有8个潜在的蛙腿基因候选者。然而，通过与人类和小鼠基因组的同线部分进行比对来增加这个数量，使该区间内的基因总数增加到约19个。在本申请中，我们寻求鉴定负责蛙腿表型的基因和特定突变。此外，我们将更好地表征蛙腿大鼠的神经系统异常。了解基因的身份和突变的性质将有助于我们进一步了解负责这种有趣的表型的分子和细胞机制。我们的工作假设是，鉴定的突变和基因负责的青蛙腿表型将提供一个新的模型，研究神经发育障碍的细胞和分子机制。因此，我们提出以下目标：具体目标1：完善青蛙腿基因座的连锁图谱。具体目的2：鉴定蛙腿基因及其突变。特定目的3：描述蛙腿大鼠表型的病理学特征。确定引起蛙腿病的基因将是确定该模型对研究神经发育障碍机制的潜在价值的重要一步。 公共卫生相关性：蛙腿大鼠是一种新的自发突变体，具有明确的后肢残疾。这种缺陷是神经学上的。随着该基因和特异性突变的鉴定，蛙腿大鼠将成为研究神经发育障碍的有价值的动物模型。

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.