Ser1遺伝子の短縮による繭層セリシンタンパク質の改変

抄録

The highly efficient genome-editing tool transcription activator-like effector nuclease (TALEN) was used to modify a Bombyx endogenous gene, Ser1, to create silkworm strains that secrete sericins of different sizes and properties. Double-stranded breaks were introduced by two pairs of TALENs that targeted the 5th and 7th exons of Ser1 to eliminate the intervening exon 6. Two mutant strains were selected, and it was confirmed that they carried truncated Ser1 genes that lacked exon 6. The cocoon sericin components of the truncated Ser1 strains were characterized using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The approximately 300-kDa sericin components, sericins M, were not detected in the homozygous Ser1 mutant cocoons, whereas they were the most abundant sericin components in the wild-type cocoons. Instead, two or three novel sericin components with lower molecular masses were observed. The truncated Ser1 cocoon shells were found to have lower sericin contents than the wild-type cocoon shells, probably because the efficiency of Ser1 production decreased in the truncated Ser1 mutants with the decrease in molecular size. The cocoon sericins were extracted more efficiently in water at 60°C and 80°C from the truncated Ser1 cocoons than from the wild-type cocoons. This is consistent with the prediction that the mutant Ser1 proteins would show higher solubility in water because of less amount of the β-sheet structure. The truncated Ser1 mutant silkworms tended to fail in spinning and often made coarse cocoons. However, they excreted silk proteins by reduced feeding in the last larval instar stage.