Expression analysis and characteristics of profilin gene from silkworm, Bombyx mori

BmCBP Catalyzes the Acetylation of BmApoLp-II Protein and Regulates Its Stability in Silkworm, Bombyx mori

Acetylation is an important and reversible post-translational modification (PTM) of protein, which is involved in many cellular physiological processes. In previous studies, lots of nutrient storage proteins were found to be highly acetylated in silkworms, and acetylation can improve the stability of these proteins. However, the related acetyltransferase was not involved. In the present work, a Bombyx mori nutrient storage protein, apolipophorin II (BmApoLp-II), was further confirmed to be acetylated, and the acetylation could improve its protein expression. Furthermore, RNAi and Co-IP showed that the acetyltransferase BmCBP was found to catalyze the acetylation modification of BmApoLp-II, and thus affect its protein expression. Meanwhile, it was proved that acetylation could improve the stability of the BmApoLp-II protein by completing its ubiquitination. These results lay a foundation for further study on the mechanism of regulating nutrition storage and hydrolysis utilization of storage proteins by BmCBP and the acetylation in the silkworm Bombyx mori.

Cloning and expression characteristics of the notch-associated gene BmE(spl)mγ from silkworm, Bombyx mori

The E(spl)mγ gene in Drosophila is a regulatory target gene downstream of the Notch pathway. BmE(spl)mγ (Bombyx mori, E(spl)mγ) is an ortholog of the Drosophila E(spl)mγ gene, and the gene encodes a protein with 248 amino acid residues. This gene was cloned and overexpressed in Escherichia coli BL21(DE3). The recombinant protein was purified and subsequently used to generate a rabbit polyclonal antibody. Western blotting analyses showed that BmE(spl)mγ expression is high in pupa and egg, and low in larva and moth. In the fifth instar larva, the protein levels are high in head, epidermis, sexual gland, trachea, and the fatbody and low in the Malpighian tubule, hemolymph, gut, and silk gland. The further immunohistochemical analyses also showed higher BmE(spl)mγ expression in the head of fifth instar larva and pupa. Of the four moth parts studied, the thorax had the highest expression level. Thus, BmE(spl)mγ might be associated with neurogenesis in silkworm. Furthermore, DAPT (a γ-secretase inhibitor and an indirect inhibitor of Notch) blocking experiments showed that higher concentrations of the blocking agent and a longer processing time reduce the transcription levels of the BmE(spl)mγ gene, demonstrating that the silkworm BmE(spl)mγ gene is associated with the Notch signal pathway. These findings suggest that the function of BmE(spl)mγ may be similar to that of its Drosophila homolog.

RIP-seq of BmAgo2-associated small RNAs reveal various types of small non-coding RNAs in the silkworm, Bombyx mori

Background

Small non-coding RNAs (ncRNAs) are important regulators of gene expression in eukaryotes. Previously, only microRNAs (miRNAs) and piRNAs have been identified in the silkworm, Bombyx mori. Furthermore, only ncRNAs (50-500nt) of intermediate size have been systematically identified in the silkworm.

Results

Here, we performed a systematic identification and analysis of small RNAs (18-50nt) associated with the Bombyx mori argonaute2 (BmAgo2) protein. Using RIP-seq, we identified various types of small ncRNAs associated with BmAGO2. These ncRNAs showed a multimodal length distribution, with three peaks at ~20nt, ~27nt and ~33nt, which included tRNA-, transposable element (TE)-, rRNA-, snoRNA- and snRNA-derived small RNAs as well as miRNAs and piRNAs. The tRNA-derived fragments (tRFs) were found at an extremely high abundance and accounted for 69.90% of the BmAgo2-associated small RNAs. Northern blotting confirmed that many tRFs were expressed or up-regulated only in the BmNPV-infected cells, implying that the tRFs play a prominent role by binding to BmAgo2 during BmNPV infection. Additional evidence suggested that there are potential cleavage sites on the D, anti-codon and TψC loops of the tRNAs. TE-derived small RNAs and piRNAs also accounted for a significant proportion of the BmAgo2-associated small RNAs, suggesting that BmAgo2 could be involved in the maintenance of genome stability by suppressing the activities of transposons guided by these small RNAs. Finally, Northern blotting was also used to confirm the Bombyx 5.8 s rRNA-derived small RNAs, demonstrating that various novel small RNAs exist in the silkworm.

Conclusions

Using an RIP-seq method in combination with Northern blotting, we identified various types of small RNAs associated with the BmAgo2 protein, including tRNA-, TE-, rRNA-, snoRNA- and snRNA-derived small RNAs as well as miRNAs and piRNAs. Our findings provide new clues for future functional studies of the role of small RNAs in insect development and evolution.

Construction of the ie1-Bacmid expression system and its use to express EGFP and BmAGO2 in BmN cells

The presently available expression tools and vectors (e.g., eukaryotic expression vectors and the adenovirus expression system) for studying the functional genes in Bombyx mori are insufficient. The baculovirus expression system is only used as a protein production tool; therefore, recombinant proteins expressed by B. mori using the baculovirus expression system equipped with a polyhedrin promoter cannot be used for in vivo research applications. In this work, we constructed and screened a eukaryotic expression vector for silkworm cells The EGFP and B. mori Argonaute2 proteins were found to be efficiently expressed using the screened pIEx-1 vector with the FuGENE 6 transfection reagent. Additionally, we constructed a novel nucleopolyhedrovirus ie1-Bacmid expression system for the production of recombinant protein; we then used the system to highly express the EGFP and B. mori Argonaute2 proteins. In this system, the protein of interest can be efficiently expressed 13 h after infection by controlling the B. mori nucleopolyhedrovirus immediate early ie1 promoter. The ie1-Bacmid system provides a powerful "adenovirus-like" expression tool; not only can the tool be used to study baculovirus molecular biology for the silkworm but it is also useful in other research applications as well, such as the study of gene functions involved in cellular physiological processes.

Profilin is associated with transcriptionally active genes

We have raised antibodies against the profilin of Chironomus tentans to study the location of profilin relative to chromatin and to active genes in salivary gland polytene chromosomes. We show that a fraction of profilin is located in the nucleus, where profilin is highly concentrated in the nucleoplasm and at the nuclear periphery. Moreover, profilin is associated with multiple bands in the polytene chromosomes. By staining salivary glands with propidium iodide, we show that profilin does not co-localize with dense chromatin. Profilin associates instead with protein-coding genes that are transcriptionally active, as revealed by co-localization with hnRNP and snRNP proteins. We have performed experiments of transcription inhibition with actinomycin D and we show that the association of profilin with the chromosomes requires ongoing transcription. However, the interaction of profilin with the gene loci does not depend on RNA. Our results are compatible with profilin regulating actin polymerization in the cell nucleus. However, the association of actin with the polytene chromosomes of C. tentans is sensitive to RNase, whereas the association of profilin is not, and we propose therefore that the chromosomal location of profilin is independent of actin.

Molecular characterization, tissue distribution, subcellular localization and actin-sequestering function of a thymosin protein from silkworm

We identified a novel gene encoding a Bombyx mori thymosin (BmTHY) protein from a cDNA library of silkworm pupae, which has an open reading frame (ORF) of 399 bp encoding 132 amino acids. It was found by bioinformatics that BmTHY gene consisted of three exons and two introns and BmTHY was highly homologous to thymosin betas (Tβ). BmTHY has a conserved motif LKHTET with only one amino acid difference from LKKTET, which is involved in Tβ binding to actin. A His-tagged BmTHY fusion protein (rBmTHY) with a molecular weight of approximately 18.4 kDa was expressed and purified to homogeneity. The purified fusion protein was used to produce anti-rBmTHY polyclonal antibodies in a New Zealand rabbit. Subcellular localization revealed that BmTHY can be found in both Bm5 cell (a silkworm ovary cell line) nucleus and cytoplasm but is primarily located in the nucleus. Western blotting and real-time RT-PCR showed that during silkworm developmental stages, BmTHY expression levels are highest in moth, followed by instar larvae, and are lowest in pupa and egg. BmTHY mRNA was universally distributed in most of fifth-instar larvae tissues (except testis). However, BmTHY was expressed in the head, ovary and epidermis during the larvae stage. BmTHY formed complexes with actin monomer, inhibited actin polymerization and cross-linked to actin. All the results indicated BmTHY might be an actin-sequestering protein and participate in silkworm development.

Molecular cloning and expression characterization of translationally controlled tumor protein in silkworm pupae

A Bombyx mori (B. mori) cDNA was isolated from silkworm pupae cDNA library encoding a homologue of translationally controlled tumor protein (BmTCTPk). BmTCTPk was expressed in E. coli; SDS-PAGE and Western blot showed the molecular weight of recombinant and native BmTCTPk is approximately 28 and 25 kDa, respectively; they are larger than the theoretical molecular weight. Immunohistochemical studies showed that BmTCTPk is uniformly distributed throughout the cytoplasm of BmN cells. In silkworm pupae, BmTCTPk is expressed in the midgut wall, the midgut cavity, and some fat body tissues lying between the midgut wall and body wall. Western blot and ELISAs performed on total protein extracts isolated from silkworm pupae at different development stages showed that, although BmTCTPk is expressed during all pupae stages, its expression level increases dramatically during late pupae stages, suggesting that BmTCTPk may play an important role during the developmental transition from pupa to imago.