A novel splice variant of the decapentaplegic (dpp) gene in the wild silkworm, Bombyx mandarina

BmHpo mutation induces smaller body size and late stage larval lethality in the silkworm, Bombyx mori

As a core member of the Hippo signaling pathway, Hpo plays a critical role in regulating growth and development. Previous studies reported that loss of function of Hpo results in increased proliferation, reduced apoptosis and induction of tissue overgrowth in Drosophila. In this study, we used CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats/Cas9) to study Hpo gene (BmHpo) function in the lepidopteran insect Bombyx mori, known commonly as the silkworm. Sequence analysis of BmHpo revealed an array of deletions in mutants. We found that BmHpo knockout resulted in defects in body size regulation, in developmental defects and pigment accumulation and early death. Our data show that BmHpo is essential for regulation of insect growth and development and that CRISPR/Cas9 technology can serve as a basis for functional analysis of target genes in lepidopteran insects.

Genome editing reveals the function of Yorkie during the embryonic and early larval development in silkworm, Bombyx mori

As a transcriptional coactivator, Yorkie (Yki) is a major downstream target of the Hippo signalling pathway to regulate the organ size during animal development and regeneration. Previous microarray analysis in the silkworm, Bombyx mori, has shown that genes associated with the Hippo pathway were primarily expressed in gonads and imaginal discs. The RNA-interference-mediated silencing of Yki at the early wandering stage delayed B. mori development and ovary maturation, whereas baculovirus-mediated overexpression at the late larval instar facilitated organ growth and accelerated metamorphosis. Here, we employed CRISPR/Cas9-mediated mutagenesis to investigate the function of Yki in B. mori (BmYki) at the embryonic and early larval stages. Knocking out of BmYki led to reduced body size, moulting defects and, eventually, larval lethality. Sequence analysis of CRISPR/Cas9 mutants exhibited an array of deletions in BmYki. As a critical downstream effector of the Hippo kinase cassette, silencing of BmYki at the embryonic stage is indispensable and the consequence is lethal. Given that the Hippo signalling pathway is evolutionarily conserved, Yki has the potential to be a novel molecular target for genetic-based pest management practices.

Bombyx mori hemocyte extract has anti-inflammatory effects on human phorbol myristate acetate-differentiated THP‑1 cells via TLR4-mediated suppression of the NF-κB signaling pathway

Hemolymph is the circulating fluid of insects and is a key component of their immune system. However, little is known concerning hemocyte identification, development, differentiation and related cellular immune responses. The present study aimed to determine whether a hemocyte extract prepared from Bombyx mori larvae had anti-inflammatory effects; THP-1 (a human monocytic leukemia cell line) cells that had been differentiated into macrophage-like cells by treatment with phorbol myristate acetate (PMA) were used. THP-1 cells were cultured with different concentrations of a B. mori hemocyte extract prior to exposure to lipopolysaccharide (LPS) to induce an inflammatory response. The effects of the B. mori hemocyte extract on anti-inflammatory pathways were determined using reverse transcription-quantitative polymerase chain reaction and western blotting to assess the expression of pro-inflammatory molecules. The B. mori hemocyte extract inhibited the LPS-induced mRNA expression of Toll-like receptor 4 in addition to LPS-induced interleukin (IL)-1β, IL-6, IL-8 and tumor necrosis factor-α. Treatment of PMA-differentiated THP-1 cells with B. mori hemocyte extract also inhibited inducible nitric oxide synthase and cyclooxygenase-2 transcription and translation. Nuclear factor-κB activation and phosphorylation also decreased. Further in-depth functional studies are required to understand the mechanism underlying the anti-inflammatory effects of silkworm hemocyte extract.