ISOLATION AND MAPPING OF NOVEL MOUSE-BRAIN CDNA CLONES CONTAINING TRINUCLEOTIDE REPEATS, AND DEMONSTRATION OF NOVEL ALLELES IN RECOMBINANT INBRED STRAINS

Abnormal expansion of trinucleotide repeats (TRs) has now been implica ted in the pathogenesis of at least nine human genetic disorders, part icularly those in which anticipation and/or fragile sites have been de monstrated. Anticipation, the phenomenon of increasing severity of phe notype in successive generations, has never been seen in species other than man. Nevertheless, animal models for the dynamic mutation of TRs would be extremely valuable. We have screened a mouse brain cDNA libr ary in an attempt to identify clones representing each of the 10 possi ble classes of trinucleotide repeat. Thirty-seven clones were analyzed in detail. Of the 37 sequences, 18 displayed significant levels of ho mology with sequences in GenBank, 10 of them with human expressed sequ ence tags (ESTs). We then analyzed 25 of the clones by PCR of the sequ ence containing the repeat in a number of different mouse strains and species to assess levels of variability of repeat length. Of the 25 cl ones analyzed in this way, 64% showed length variation between Mus mus culus spp. and Mus spretus, and 32% showed variation between Mus muscu lus musculus-derived standard laboratory inbred strains. Where variati on was detected (17 repeat-containing clones in all), the gene was map ped by linkage analysis. None of the repeats isolated showed any signs of extreme expansion. However, two of the repeats were shown to have undergone size changes during the establishment of a number of recombi nant inbred strains, suggesting that these repeats are at least modera tely unstable.