In the silkworm, Bombyx mori, there are 30 kDa proteins that are expressed in the fat body and secreted into the hemolymph. A 19G1-30 kDa protein in the membrane fraction of the late larval midgut is a probable receptor for the hemolymph chymotrypsin inhibitor CI-8. Take-up of CI-8 into the pupal perivisceral fat body suggests that the 19G1-30 kDa proteins function as a receptor in the fat body. We used biochemical assays to investigate whether the 19G1-30 kDa proteins were the receptor for CI-8 in the pupal fat body. The results of affinity purification, far western blotting, and western blotting suggested that the 19G1-30 kDa proteins are the interacting factors of the membrane fraction of the pupal fat body. Tissue surface analysis indicated that these proteins were the canonical tissue-surface proteins. Immunological analysis showed that, after the take-up of CI-8 into the fat body, dissociation of the 19G1-30 kDa protein and CI-8 occurred followed by aggregation of the 19G1-30 kDa proteins to form protein granules. The results showed that the 19G1-30 kDa protein is a receptor of CI-8.

 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.