DNA sequence analysis of a chromosomal aberration in irradiation induced burnt (Bu) mutant of Bombyx mori

The radiation-induced mutations burnt (Bu) and non-preference A4 (Np-A4) map to chromosome 11 in Bombyx mori. Bu causes irregularly shaped fifth to eighth larval segments, whereas Np-A4 causes one of the polyphagous phenotypes, i.e., feeding on non-mulberry leaves. Homozygotes and trans heterozygotes of these mutations die during embryogenesis, suggesting that the lethality associated with Bu and Np-A4 is allelic. Genetic studies of the Bu and Np-A4 mutation would provide a better understanding of the embryogenesis, morphogenesis, and feeding behavior of B. mori. Here we conducted a molecular analysis of the Bu locus. In our crossing experiments, larvae carrying both the Bu and Np-A4 mutations appeared, although they were hypothesized to die during embryogenesis. A detailed analysis of the survivors resulted in the identification of a breakage event on chromosome 11. Moreover, it was revealed that the survivors exhibited partial trisomy. Using DNA sequence analysis, the breakpoint in chromosome 11 was narrowed to an intron of Bmzfh3. Embryonic lethality associated with the breakage of the chromosome 11 is discussed.