Abstract
We found highly unstable DNA sequences (AT-rich) during the study of genetic effects of radiation on mouse by 2D genome scanning.
Among 368 F1 mice, we found 18 mutations after screening 514 paternal BALB/c spots per mouse (32P labeled DNA at AflII (C/TTAAG) sites). Among the 18 mutations, 7 occurred at the same s754 spot as a result of three independent events, which gave the spontaneous mutation rate of 0.8% per generation. The s754 is one of the spots appearing on a same horizontal line on a 2D pattern. These spots were highly polymorphic among strains of laboratory mouse, and 40 spots differed already between the two closely related C57BL/6N and /6J strains. Three of these spots were cloned and found that the sequence was identical or almost identical to s754 sequence from BALB/c mouse. 2D Southern analysis using the s754 DNA as a probe showed spots at identical positions as we see on the 2D DNA gel in C57BL/6N, C57BL/6J, BALB/c and C3H mice. Thus, these aligned spots belong to the same family. Ordinary 1D Southern analysis using the same probe revealed the same size of bands on 17 M.mus DNA samples but no bands were detected on the samples from M.spretus, rat, or human. Although BLAST search revealed two BAC clones that contained the s754 sequences, no exactly matched sequences were found in the mouse draft sequences. This implies that the s754 sequences are in the gap of the draft sequences. The s754 sequence is specific to M.mus but the origin and the reasons for the instability remain unknown.
