Mice heterozygous for the trembler-Jackson spontaneous mutation (Pmp22Tr-J) are similar to heterozygotes carrying the original trembler mutation (Pmp22Tr). However, the behavior and neuropathology of trembler-Jackson heterozygotes is less severe. The tremor phenotype cannot be reliably recognized before 20 to 25 days. There are no obvious seizures and only a mild gait abnormality. In the PNS, the myelin deficiency is considerably less severe than that of trembler mice. Homozygous trembler-Jackson mice are recognizable by 8 days of age after which they become progressively disabled. Homozygous mutant mice are unable to walk normally and can right themselves only with great difficulty; most are dead by 18 days. It should be noted that although trembler homozygotes are more severely demyelinated than trembler-Jackson homozygotes, the trembler mice live a normal lifespan while trembler-Jackson mice die prior to weaning. Survival of trembler homozygotes suggests that peripheral myelin is not essential for survival. The PNS is nearly devoid of myelin with myelinogenesis blocked in the promyelin stage. Schwann cells ensheathe individual axons but without formation of compact myelin. This C57BL/6 congenic strain is also carrying the dominant rex spontaneous mutation (Krt25Re) that is also located on Chromosome 11.

These mice carry two linked, spontaneous mutations, trembler-Jackson (Pmp22Tr-J) and rex (Krt25Re). They are characterized by becoming progressively disabled with inability to walk and right themselves. The rex mutation is characterized by curly whiskers and wavy coats.

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