Effects of transgenic overexpression of diapause hormone and diapause hormone receptor genes on non-diapause silkworm

The endocrine disruptor, fenoxycarb modulates gut immunity and gut bacteria titer in the cotton bollworm, Helicoverpa armigera

The endocrine system modulates several physiological functions such as development and metamorphosis in insects. The normal growth and development of insects is interfered with insect growth regulators (IGRs), which act as mimics of insect hormones like juvenile hormone (JH) and ecdysone hormone. The effects of JH and its analogs on systemic immunity have been identified. However the effect of these compounds on local gut immunity is largely unknown. In this study, the effects of JH analog fenoxycarb on the local gut immunity of Helicoverpa armigera, gut bacteria population, and their role in the pathogenicity of Bacillus thuringiensis (Bt) were analyzed. The results showed that feeding fenoxycarb causes a decrease in the transcription level of IMD (Relish and PGPR-LC), ROS (DUOX and SOD) related genes and antimicrobial peptides (AMPs), followed by an overpopulation of gut bacteria. The fenoxycarb-treated larvae showed higher susceptibility to Bt compared to the control larvae. Overall, these findings collectively suggest that JH analog affects local gut immunity and gut bacteria titer.

Mutation of a lepidopteran-specific PMP-like protein, BmLSPMP-like, induces a stick body shape in silkworm, Bombyx mori

BACKGROUND

Lepidoptera is one of the largest orders of insects, some of which are major pests of crops and forests. The cuticles of lepidopteran pests play important roles in defense against insecticides and pathogens, and are indispensable for constructing and maintaining extracellular structures and locomotion during their life cycle. Lepidopteran-specific cuticular proteins could be potential targets for lepidopteran pest control. But information on this is limited. Our research aimed to screen the lepidopteran-specific cuticular proteins using the lepidopteran model, the silkworm, to explore the molecular mechanism underlying the involvement of cuticular proteins in body shape construction.

RESULTS

Positional cloning showed that BmLSPMP-like, a gene encoding a lepidopteran-specific peritrophic matrix protein (PMP) like protein which includes a peritrophin A-type chitin-binding domain (CBM_14), is responsible for the stick (sk) mutation. BmLSPMP-like is an evolutionarily conserved gene that exhibits synteny in Lepidoptera and underwent purifying selection during evolution. Expression profiles demonstrated that BmLSPMP-like is expressed in chitin-forming tissues, testis and ovary, and accumulates in the cuticle. BmLSPMP-like knockout, generated with CRISPR/Cas9, resulted in a stick-like larval body shape phenotype. Over-expression of BmLSPMP-like in the sk mutant rescued its abnormal body shape. The results showed that BmLSPMP-like may be involved in assemblage in the larval cuticle.

CONCLUSION

Our results suggested that the dysfunction of BmLSPMP-like may result in a stick body shape phenotype in silkworm, through the regulation of the arrangement of the chitinous laminae and cuticle thickness. Our study provides new evidence of the effects of LSPMP-likes on lepidopteran body shape formation, metamorphosis and mortality, which could be an eco-friendly target for lepidopteran pest management. © 2022 Society of Chemical Industry.

Transcriptional Dynamics Induced by Diapause Hormone in the Silkworm, Bombyx mori

Diapause is a form of dormancy that organisms use to adapt to extreme environments by exhibiting developmental arrest. In the silkworm, Bombyx mori, diapause is thought to be elicited by diapause hormone (DH) signaling, which consists of interactions between DH and the DH receptor (DHR). However, the steps downstream of the DH signaling pathway are largely unknown. In the present study, we directly injected synthesized DH into the female pupae of a multivoltine, non-diapausing strain at 36 h after pupation. We found that the mRNA level of DHR declined at 4 h and recovered at 12 h after the injection of DH. Thus, we sequenced the transcriptome of the ovaries at 4 h and 12 h after the injection of DH. We identified 60 and 221 differentially expressed genes at 4 h and 12 h after the injection, respectively. All DEGs were identified, relating to 20E-related genes, JH-related genes, cellular detoxification, ribosomal proteins, lipid metabolism, and epigenetic modifications. Eleven genes were selected from the above categories to verify the transcriptome data. The qRT-PCR and RNA-Seq expression patterns of the genes were consistent, which indicated the authenticity and reliability of the transcriptome data. This study dramatically expands upon our knowledge of gene expression variation at the early phase of DH release.

Circadian Clock Gene Period Contributes to Diapause via GABAeric-Diapause Hormone Pathway in Bombyx mori

Diapause is a developmental transition in insects based on seasonal adaptation to adversity; it is regulated by a circadian clock system and the endocrine system. However, the molecular node and its mechanism underlying the effects of these systems are still unclear. Here, a mutant of Bombyx mori with the circadian clock gene Period (Per) knocked out was constructed, which dramatically changed the classic diapause-destined pathway. Per-knockout silkworms powerfully attenuated, but could not completely block, the predetermined effects of temperature and photoperiod on diapause determination, and this effect depended on the diapause hormone (DH) pathway. The impaired transcription-translation feedback loop of the circadian clock system lacking the Per gene caused direct up-regulation of the expression of GRD, a receptor of γ-aminobutyric acid (GABA), by changing expression level of Cycle. The synthesis of GABA in the tissue complex of brain-suboesophageal ganglion then increased and restricted the decomposition, which continuously promoted the GABAergic signal to play a role, and finally inhibiting (delaying) the release of DH to the hemolymph, and reducing the diapause-inducing effect of DH. The results provided an example to explain the regulatory mechanism of the circadian clock on endocrine hormones in the silkworm.

The intronic promoter of Actin4 mediates high-level transgene expression mainly in the wing and epidermis of silkworms

The cytoplasmic actin gene Actin4 (A4) in silkworm (Bombyx mori) was isolated 20 years ago and has a distal promoter upstream of the first exon and a proximal promoter within the first intron; however, how the promoter regulates gene expression has yet to be fully elucidated. Here, we characterized the function and expression of the proximal promoter (named A4IP) by analyzing transgenic Gal4/UAS silkworms, A4IP-Gal4/UAS-EGFP. We demonstrated that A4IP drives the expression of Gal4 and thereby activates UAS-linked EGFP in transgenic silkworms beginning in day-3 embryos through adults. Further detection revealed that EGFP was expressed at a low level in tissues including the trachea, fat body and midgut but was highly expressed in the wing disks/wings and inner epidermis of transgenic silkworms. No EGFP signals were detected in other tissues by western blot assay. Interestingly, EGFP fluorescence had a spot-like distribution on the epidermis of transgenic larvae. These observations are quite different from those in transgenic silkworms driven by the promoter of Actin3 (A3), another cytoplasmic actin gene in B. mori. These findings reveal the expression profiles of the A4IP promoter and provide new insights into the regulatory mechanism of cytoplasmic actin genes in silkworms.

Genome-wide analysis of developmental stage-specific transcriptome in Bradysia odoriphaga

Bradysia odoriphaga is a serious pest of the Chinese chive; however, detailed information regarding the developmental stage-specific gene expression patterns of B. odoriphaga is not yet available. In this study, RNA sequencing (RNA-seq) was performed to determine the gene expression patterns of developmental stages including the eggs, second instar larvae, fourth instar larvae, pupae, and adults of B. odoriphaga. Analysis of 15 samples revealed an average of 89.56% of the clean reads could be mapped onto the assembled UniGene database. Cluster tree analysis showed that the expression patterns were stage-specific and that samples of the second and fourth instar larvae clustered in one group, while those of eggs, pupae, and adults clustered in another group. Differential expression unigenes (DEUs) for sequential developmental stages were between 3314 and 10,632. A total of 1910-7756 DEUs of sequential developmental stages were assigned into 45-56 gene ontology categories and 1165-3845 DEUs were mapped into Kyoto Encyclopedia of Genes and Genomes pathways. The expression of DEUs related to growth and development showed that hormone receptors highly expressed in the pupal stage, while chitinases were highly expressed in the larval stage. The results of quantitative real time polymerase chain reaction (qRT-PCR) and RNA-seq expression agreed well for 12 growth- and development-related unigenes. This study identified DEUs for sequential developmental stages of B. odoriphaga. Gene Ontology classifications and KEGG pathway identification of DEUs not only provide information useful for understanding insect growth and development but also for exploring novel approaches to control B. odoriphaga.