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Background: In Bombyx mori, the genes responsible for silk biosynthesis appear to be controlled by hormones. Results: Bmdimm is specifically expressed in silk glands and directly regulates the expression of fibroin H-chain (fib-H) by the juvenile hormone (JH)-Met-Kr-h1 pathway. Conclusion: JH is involved in synthesis of fib-H through Bmdimm. Significance: This pathway provides new insights into hormonal regulation of silk protein genes.

Silk glands are specialized in the synthesis of several secretory proteins. Expression of genes encoding the silk proteins in Bombyx mori silk glands with strict territorial and developmental specificities is regulated by many transcription factors. In this study, we have characterized B. mori sage, which is closely related to sage in the fruitfly Drosophila melanogaster. It is termed Bmsage; it encodes transcription factor Bmsage, which belongs to the Mesp subfamily, containing a basic helix–loop–helix motif. Bmsage transcripts were detected specifically in the silk glands of B. mori larvae through RT-PCR analysis. Immunoblotting analysis confirmed the Bmsage protein existed exclusively in B. mori middle and posterior silk gland cells. Bmsage has a low level of expression in the 4th instar molting stages, which increases gradually in the 5th instar feeding stages and then declines from the wandering to the pupation stages. Quantitative PCR analysis suggested the expression level of Bmsage in a high silk strain was higher compared to a lower silk strain on day 3 of the larval 5th instar. Furthermore, far western blotting and co-immunoprecipitation assays showed the Bmsage protein interacted with the fork head transcription factor silk gland factor 1 (SGF1). An electrophoretic mobility shift assay showed the complex of Bmsage and SGF1 proteins bound to the A and B elements in the promoter of fibroin H-chain gene(fib-H), respectively. Luciferase reporter gene assays confirmed the complex of Bmsage and SGF1 proteins increased the expression of fib-H. Together, these results suggest Bmsage is involved in the regulation of the expression of fib-H by being together with SGF1 in B. mori PSG cells.

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Synthetic work by several groups led to revision of the structure initially proposed for prekinamycin to 1. 1 We have achieved a brief regiospecific preparation of 1 based on use of our phthalide annelation methodology. 2 In accomplishing this preparation, we have established that the anion of the phthalide 5 readily undergoes condensations with indenones such as 4, a class of compounds not previously investigated as acceptors. 3 As indicated in Scheme 1, the indenone 4 needed for the phthalide annelation was prepared from the dihydrocoumarin 2. Intramolecular Friedel-Crafts rearrangement 4 of 2 (AlCl 3 /NaCl, 180°C, 1 h), followed by methylation (DMSO 4 , K 2 CO 3 , acetone), furnished 3 in 60% overall yield. As a class of compounds, indenones are unstable materials, 5 and attempted application of a procedure previously established to convert indanones to indenones 6 gave only a modest yield of 4 from 3. Ultimately we were able to prepare 4 in satisfactory yield (75%) via conversion of 3 to the silyl enol ether (TMSTf, Et 3 N), followed by treatment with Pd(OAc) 2 . 7