Expression profiles of the genes for nine transcription factors and their isoforms in the posterior silk gland of the silkworm Bombyx mori during the last and penultimate instars

抄録

We analyzed expression patterns in nine transcription factor genes and their isoforms in the posterior silk gland (PSG) of the silkworm Bombyx mori during the fourth and fifth instars. Two subtypes (-A and -B1) of EcR mRNA were expressed as almost corresponding to the change in ecdysone levels, but two subtypes (-1 and -2) of usp mRNA were controlled differently. The expression of usp-1 mRNA was suppressed at the peak of the ecdysone level and also at the expression peaks of EcR-A and usp-2 RNAs during the fourth instar. The β-isoform-specific region of the FTZ-F1 gene was identified, and distinct temporal expression patterns of the α-and β-isoforms of FTZ-F1 mRNA were detected using isoform-specific probes. The β-isoform peaked in the fourth molting stage, while the α-isoform was increased after the fourth ecdysis. The expression patterns of the βFTZ-F1 and BR-C genes showed the best reversed images relative to those of the silk protein genes. The genes for transcription factors (Fkh/SGF-1, FMBP-1, Awh and Ubx) predicted to be involved in the activation of the fibroin gene were expressed not only in the feeding stages but also in the fourth molting stage when the fibroin gene is suppressed. In addition, we found that the Bombyx Arrowhead (Awh) gene generated a male-specific splice variant in the PSG and gonad. These findings provide new insights into regulatory mechanisms for the silk protein genes.