Newly ecdysed fifth instar larvae of the Bombyx mori strain N4 were divided into three groups and fed one of three different diets until they began spinning a cocoon. One group was fed the basal diet, in which carotenoids consisted mainly of lutein (53.3μg/g wet) and β-carotene (14.4μg/g wet), while the two other groups were fed the basal diet supplemented with astaxanthin from AstaREAL® or capsanthin from paprika-red®. High performance liquid chromatography was performed to identify the carotenoids in lipophorin, the middle silk glands, and the cocoons. Lutein, as well as astaxanthin and capsanthin, was accumulated in the cocoons after feeding with the astaxanthin- or capsanthin-supplemented diet. Quantitative analysis of the strain N4 and c10 demonstrated competitive accumulation in the cocoon between lutein and astaxanthin. In fifth instar larvae of the white cocoon producer, the strain c05 fed a diet containing lutein and astaxanthin, however, they produced only white cocoon. These results indicated that lutein and astaxanthin transport share common pathways, and that the delivery system in the silkworm can mediate the transfer and accumulation of carotenoids which are not derived from mulberry leaves, such as astaxanthin and capsanthin.

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The insect steroid hormone, ecdysone, initiates larval ecdysis and metamorphosis in many insects by activating a cascade of genes—beginning with early genes, most of which encode transcriptional regulators. One of the early genes, Broad-Complex (BR-C) encodes a BTB zinc-finger protein that exists as a number of isoforms generated by alternative splicing. The isoforms are categorized into 4 classes (Z1 to 4) according to the sequence of their zinc-finger domain. A BR-C Z3-isoform is expressed in the Drosophila larval salivary gland and fat body. By contrast, in Bombyx, the BR-C homologue (BmBR-C) Z3-isoform has not yet been detected, even though a Z3-type zinc-finger coding sequence is found in the genome.
In this study, cDNAs encoding the Z2-isoform, carrying a partial (Z2/3s) or a full-length (Z2/3) sequence of an additional exon (exon 13), including an out of frame Z3-type zinc-finger coding sequence were cloned. BmBR-C is transcribed from two different promoters. One is the ecdysone-inducible distal promoter (Pdist), and the other is the ecdysone-noninducible proximal promoter (Pprox). When the broad category of Z2-isoforms was abundantly expressed from either promoter, the transcripts were predominantly composed of the Z2/3-isoform. In these mRNAs, polyadenylation signals of the “variant type”, located proximal to the coding sequence were used for the Z2-isoform transcripts. Additionally, one of the canonical signals, “AUUAAA”, or the variant type signals located at the 3’-most site was used as a polyadenylation signal for the Z2/3-isoform transcripts. The different signal usage may play a role in the polyadenylation rate of the Z2 and Z2/3-isoforms.

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We previously showed that rRNA cleavage and degradation occur in Bombyx mori BM-N cells upon infection with heterologous NPVs, including Autographa californica multiple NPV (AcMNPV), Hyphantria cunea MNPV, Spodoptera exigua MNPV, and Spodoptera litura MNPV. Additionally, transient expression assay analyses suggested that viral P143s, which are baculovirus DNA helicases that are essential for viral DNA replication, are responsible for the observed rRNA cleavage and degradation. Here, we examined whether viral DNA replication is related to rRNA cleavage and degradation in AcMNPV-infected BM-N cells using an AcMNPV temperature-sensitive-mutant (ts8) defective in P143 function at non-permissive temperature. Electrophoretic analyses of total RNAs from ts8-infected BM-N cells revealed that rRNA cleavage and degradation still occurred in the absence of viral DNA replication at non-permissive temperature. In addition, transfection analysis with an ac-p143 null AcMNPV bacmid demonstrated that the p143 gene is responsible for rRNA cleavage and degradation in AcMNPV-infected BM-N cells. Taken together, these results indicate the possibility that the viral DNA replication-related function of P143 is not associated with rRNA cleavage and degradation in NPV-infected BM-N cells.

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