A CCCH zinc finger gene regulates doublesex alternative splicing and male development in Bombyx mori

Knockout of nuclear receptor HR38 gene impairs pupal-adult development in silkworm Bombyx mori

Nuclear receptors are ligand-regulated transcription factors that play important role in regulating insect metamorphosis through the ecdysone signalling pathway. In this study, we investigated the nuclear receptor HR38 gene in Bombyx mori (BmHR38), belonging to the NR4A subfamily. BmHR38 mRNA was highly expressed in the head and epidermis at the pupal stage. The expression of the BmHR38 gene was influenced by different doses of 20E at different times. A BmHR38 deletion mutant silkworm was generated using the clustered regularly interspaced short palindromic repeat (CRISPR)/Cas9 system. Compared with the wild-type B. mori, the BmHR38 deletion mutant resulted in abnormal development during the pupal stage, leading to either failed eclosion or the formation of abnormal adult wings. After silencing of BmHR38 in the pupal stage, the phenotype of pupa or moth had no significant change, but it did result in reduced egg production. The mRNA levels of USP, E75 and E74 were significantly increased, while the transcript levels of FTZ-F1 were suppressed after RNA interference. Furthermore, interference with BmHR38 also inhibited the expressions of chitin metabolism genes, including Chs1, Chs2, Chi, Chi-h and CDA. Our results suggest that BmHR38 is essential for pupal development and pupa-adult metamorphosis in B. mori by regulating the expression of NRs and chitin metabolism genes.

A Protein Asteroid with PIN Domain in Silkworm Bombyx mori Is Involved in Anti-BmNPV Infection

Nuclease is a type of protein that degrades nucleic acids, which plays an important role in biological processes, including RNA interference efficiency and antiviral immunity. However, no evidence of a link between nuclease and Bombyx mori nucleopolyhedrovirus (BmNPV) infection in silkworm B. mori has been found. In this study, a protein asteroid (BmAst) containing the PIN domain and XPG domain was identified in silkworm B. mori. BmAst gene was highest expressed in hemocytes and fat body of the 5th instar larvae, and high expression in the pupa stage. The transcriptional levels of the BmAst gene in 5th instar larvae were significantly induced by BmNPV or dsRNA. After knocking down BmAst gene expression by specific dsRNA, the proliferation of BmNPV in B. mori was increased significantly, whereas the survival rate of larvae was significantly lower when compared with the control. Our findings indicate that BmAst is involved in silkworm resistance to BmNPV infection.

Cell-based analysis reveals that sex-determining gene signals in Ostrinia are pivotally changed by male-killing Wolbachia

Wolbachia, a maternally transmitted bacterium, shows male-killing, an adaptive phenotype for cytoplasmic elements, in various arthropod species during the early developmental stages. In lepidopteran insects, lethality of males is accounted for by improper dosage compensation in sex-linked genes owing to Wolbachia-induced feminization. Herein, we established Ostrinia scapulalis cell lines that retained sex specificity per the splicing pattern of the sex-determining gene doublesex (Osdsx). We found that Wolbachia transinfection in male cell lines enhanced the female-specific splice variant of Osdsx (Osdsx^F ) while suppressing the male-specific variant (Osdsx^M ), indicating that Wolbachia affects sex-determining gene signals even in vitro. Comparative transcriptome analysis isolated only two genes that behave differently upon Wolbachia infection. The two genes were respectively homologous to Masculinizer (BmMasc) and zinc finger-2 (Bmznf-2), male-specifically expressed sex-determining genes of the silkworm Bombyx mori that encode CCCH-type zinc finger motif proteins. By using cultured cells and organismal samples, OsMasc and Osznf-2 were found to be sex-determining genes of O. scapulalis that are subjected to sex-specific alternative splicing depending upon the chromosomal sex, developmental stage, and infection status. Overall, our findings expound the cellular autonomy in insect sex determination and the mechanism through which sex is manipulated by intracellular selfish microbes.

Assessment of a zinc finger protein gene (MPZC3H10) as potential RNAi target for green peach aphid Myzus persicae control

BACKGROUND

RNA interference (RNAi) has potential application in pest control, and selection of the specific target gene is one of the key steps in RNAi. As an important effector, the zinc finger protein (ZFP) gene has high similarity among aphid species, and may have potential use in an RNAi-based pest control strategy. This study assessed the control efficiency of an RNAi target, MPZC3H10, a CCCH-type ZFP gene, against green peach aphid.

RESULTS

ZC3H10 amino acid sequence similarity is more than 97.71% among the five tested aphid species: Myzus persicae, Aphis citricidus, Acyrthosiphon pisum, Diuraphis noxia and Rhopalosiphum maidis. However, no homologous sequence was found in the transcriptome of their ladybeetle predator, Propylaea japonica. Spatial expression patterns revealed that MPZC3H10 showed high expression in the muscle and fat body of M. persicae. The RNAi bioassay revealed that silencing of MPZC3H10 resulted in high mortality (53.33%) in M. persicae. By contrast, there were no observed negative effects on the growth and development of P. japonica when fed on aphids treated with double-stranded RNA (dsRNA) or injected with a "high dose" of dsRNA.

CONCLUSION

Targeting MPZC3H10 showed promising efficiency for green peach aphid control via artificially designed dsRNA, and was safe for the predatory ladybeetle. © 2022 Society of Chemical Industry.

Identification and Characterization of the Masculinizing Function of the Helicoverpa armigera Masc Gene

The Masculinizer (Masc) gene has been known to control sex development and dosage compensation in lepidopterans. However, it remains unclear whether its ortholog exists and plays the same roles in distantly related lepidopterans such as Helicoverpa armigera. To address this question, we cloned Masc from H. armigera (HaMasc), which contains all essential functional domains of BmMasc, albeit with less than 30% amino acid sequence identity with BmMasc. Genomic PCR and qPCR analyses showed that HaMasc is a Z chromosome-linked gene since its genomic content in males (ZZ) was two times greater than that in females (ZW). RT-PCR and RT-qPCR analyses revealed that HaMasc expression was sex- and stage-biased, with significantly more transcripts in males and eggs than in females and other stages. Transfection of a mixture of three siRNAs of HaMasc into a male embryonic cell line of H. armigera led to the appearance of female-specific mRNA splicing isoforms of H. armigeradoublesex (Hadsx), a downstream target gene of HaMasc in the H. armigera sex determination pathway. The knockdown of HaMasc, starting from the third instar larvae resulted in a shift of Hadsx splicing from male to female isoforms, smaller male pupa and testes, fewer but larger/longer spermatocytes and sperm bundles, delayed pupation and internal fusion of the testes and follicles. These data demonstrate that HaMasc functions as a masculinizing gene in the H. armigera sex-determination cascade.