Yu Cai

The widespread prevalence of the endosymbiotic bacterium Wolbachia among insect species relies on its ability to invade and manipulate host reproduction via several ways, among which cytoplasmic incompatibility (CI) is most studied. Two non-mutually exclusive models, the Host-Modification (HM) and the Toxin-Antidote (TA), have been proposed to explain the molecular basis of CI. Here, we investigate the CI-inducing activity of the Type III CI factors ( cifs ) from w AlbB, a strain currently being deployed to combat mosquito-borne diseases. This set of Cifs displays conserved subcellular localization dynamics in various insect cells. Both cifA and cifB are required for the induction of DNA damage in cultured cells, and transgenic Drosophila . Moreover, these cifs induce CI in Drosophila through the two-by-one manner, meaning cifA and cifB act together during spermatogenesis to induce CI, and maternal cifA can reverse the effect. Mechanistically, genetic, biochemical, cellular, and proteomic analyses reveal that this pair of cifs acts during the early stage of spermatogenesis but is dispensable in late-stage germline cells for CI induction. Collectively, our findings support the notion that w AlbB Type III cifs induce CI via a HM-based mechanism. Additional analyses suggest that different Wolbachia strains may employ distinct molecular mechanisms to induce CI.

Blood-feeding is crucial for the reproductive cycle of the mosquito Aedes aegypti, as well as for the transmission of arboviruses to hosts. It is postulated that blood meals may influence the mosquito microbiome but shifts in microbial diversity and function during digestion remain elusive. We used whole-genome shotgun metagenomics to monitor the midgut microbiome in 60 individual females of A. aegypti throughout digestion, after 12, 24, and 48 h following blood or sugar meals. Additionally, ten individual larvae were sequenced, showing microbiomes dominated by Microbacterium sp. The high metagenomic coverage allowed for microbial assignments at the species taxonomic level, also providing functional profiling. Females in the post-digestive period and larvae displayed low microbiome diversities. A striking proliferation of Enterobacterales was observed during digestion in blood-fed mosquitoes. The compositional shift was concomitant with enrichment in genes associated with carbohydrate and protein metabolism, as well as virulence factors for antimicrobial resistance and scavenging. The bacterium Elizabethkingia anophelis (Flavobacteriales), a known human pathogen, was the dominant species at the end of blood digestion. Phylogenomics suggests that its association with hematophagous mosquitoes occurred several times. We consider evidence of mutually beneficial host-microbe interactions raised from this association, potentially pivotal for the mosquito's resistance to arbovirus infection. After digestion, the observed shifts in blood-fed females’ midguts shifted to a sugar-fed-like microbial profile. This study provides insights into how the microbiome of A. aegypti is modulated to fulfil digestive roles following blood meals, emphasizing proliferation of potential symbionts in response to the dynamic midgut environment.

Background: Aedes aegypti (Ae. aegypti) is the major vector that transmits many diseases including dengue, Zika, and filariasis in tropical and subtropical regions. Due to the growing resistance to chemical-based insecticides, biological control methods have become an emerging direction to control mosquito populations. The sterile insect technique (SIT) deploys high doses of ionizing radiation to sterilize male mosquitoes before the release. The Wolbachia-based population suppression method of the incompatible insect technique (IIT) involves the release of Wolbachia-infected males to sterilize uninfected field females. Due to the lack of perfect sex separation tools, a low percentage of female contamination is detected in the male population. To prevent the unintentional release of these Wolbachia-infected females which might result in population replacement, a low dose of X-ray irradiation is deployed to sterilize any female escapees. However, it remains unclear whether these irradiation-induced male and female sterilizations share common mechanisms. Results: In this work, we set out to define the minimum dose of X-ray radiation required for complete female sterilization in Ae. aegypti (NEA-EHI strain). Further results showed that this minimum dose of X-ray irradiation for female sterilization significantly reduced male fertility. Similar results have been reported previously in several operational trials. By addressing the underlying causes of the sterility, our results showed that male sterility is likely due to chromosomal damage in the germ cells induced by irradiation. In contrast, female sterility appears to differ and is likely initiated by the elimination of the somatic supporting cells, which results in the blockage of the ovariole maturation. Building upon these findings, we identified the minimum dose of X-ray irradiation on the Wolbachia-infected NEA-EHI (wAlbB-SG) strain, which is currently being used in the IIT-SIT field trial. Compared to the uninfected parental strain, a lower irradiation dose could fully sterilize wAlbB-SG females. This suggests that Wolbachia-carrying mosquitoes are more sensitive to irradiation, consistent with a previous report showing that a lower irradiation dose fully sterilized Wolbachia-infected Ae. aegypti females (Brazil and Mexican strains) compared to those uninfected controls. Conclusions: Our findings thus reveal the distinct mechanisms of ionizing X-ray irradiation-induced male or female sterility in Ae. aegypti mosquitoes, which may help the design of X-ray irradiation-based vector control methods.

Editorial: Novel strategies for controlling mosquito-borne diseases

Background: Insects live in almost every habitat on earth. To adapt to their diverse environments, insects have developed a myriad of different strategies for reproduction reflected in diverse anatomical and behavioral features that the reproductive systems of females exhibit. Yet, ovarian development remains largely uncharacterized in most species exceptDrosophila melanogaster(D. melanogaster), a high Diptera model. In this study, we investigated the detailed developmental process of the ovary inAedes aegypti(Ae. aegypti), a major vector of various disease-causing pathogens that inhabits tropical and subtropical regions.Results: Compared withDrosophila melanogaster, a model of higher Diptera, the processes of pole cell formation and gonad establishment during embryonic stage are highly conserved inAe. aegypti. However,Ae. aegyptiutilizes a distinct strategy to form functional ovaries during larval/pupal development. First, during larval stage,Ae. aegyptiprimordial germ cells (PGCs) undergo a cyst-like proliferation with synchronized divisions and incomplete cytokinesis, leading to the formation of one tightly packed “PGC mass” containing several interconnected cysts, different fromD. melanogasterPGCs that divide individually. This cyst-like proliferation is regulated by the target of rapamycin (TOR) pathway upon nutritional status. Second, ecdysone-triggered ovariole formation during metamorphosis exhibits distinct events, including “PGC mass” breakdown, terminal filament cell degeneration, and pre-ovariole migration. These unique developmental features might explain the structural and behavioral differences betweenAedesandDrosophilaovaries. Importantly, both cyst-like proliferation and distinct ovariole formation are also observed inCulex quinquefasciatusandAnopheles sinensis, suggesting a conserved mode of ovarian development among mosquito species. In comparison withDrosophila, the ovarian development inAedesand other mosquitoes might represent a primitive mode in the lower Diptera.Conclusions: Our study reveals a new mode of ovarian development in mosquitoes, providing insights into a better understanding of the reproductive system and evolutionary relationship among insects.

Camptothecin (CPT), first isolated from Chinese tree Camptotheca acuminate, produces rapid and prolonged inhibition of DNA synthesis and induction of DNA damage by targeting topoisomerase I (top1), which is highly activated in cancer cells. CPT thus exhibits remarkable anticancer activities in various cancer types, and is a promising therapeutic agent for the treatment of cancers. However, it remains to be uncovered underlying its cytotoxicity toward germ cells. In this study we found that CPT, a cell cycle-specific anticancer agent, reduced fecundity and exhibited significant cytotoxicity toward GSCs and two-cell cysts. We showed that CPT induced GSC loss and retarded two-cell cysts differentiation in a niche- or apoptosis-independent manner. Instead, CPT induced ectopic expression of a differentiation factor, bag of marbles (Bam), and regulated the expression of cyclin A, which contributed to GSC loss. In addition, CPT compromised two-cell cysts differentiation by decreasing the expression of Bam and inducing cell arrest at G1/S phase via cyclin A, eventually resulting in two-cell accumulation. Collectively, this study demonstrates, for the first time in vivo, that the Bam–cyclin A axis is involved in CPT-mediated germline stem cell loss and two-cell cysts differentiation defects via inducing cell cycle arrest, which could provide information underlying toxicological effects of CPT in the productive system, and feature its potential to develop as a pharmacology-based germline stem cell regulation agent.

The apoptosis of granulosa cells can result in follicular atresia, a key process in follicle selection and development. The related molecular mechanisms were explored to study the effects of liver receptor homolog-1 (Lrh-1) on apoptosis, sodium-titanium system, and steroid synthesis of granulosa cells from Hu sheep in vitro. After constructing, designing, and synthesizing the Lrh-1 overexpression vector, liposomes were used to transfect Hu sheep granulosa cells. Thereafter, qRT-PCR and Western blot were used to detect the mechanism of Lrh-1 on the titanium system and steroid synthesis of Hu sheep granulosa cells. The overexpression efficiency was determined by fluorescence 48 h after liposome transfection into the Hu sheep granulosa cells in vitro culture. The transfection efficiency was higher, hence providing a basis for subsequent experiments. However, the protein level and transcriptional level of Lrh-1 significantly increased after transfection with Lrh-1 overexpression vector in Hu sheep granulosa cells. We further revealed that after Lrh-1 overexpression in Hu sheep granulosa cells, the expression of the pro-apoptotic gene Bax decreased significantly, while that of the anti-apoptotic gene Bcl-2 increased significantly, as well as the sodium peptide system. Moreover, the expression levels of natriuretic peptide precursor A, B, and C (NPPA, NPPB, NPPC) all showed an upward trend, while the expression levels of steroid synthesis-related genes (P450arom and P450scc) decreased. The above results showed that Lrh-1 overexpression influenced the apoptosis, sodium peptide system, and steroid synthesis.

Stem cells have the potential to maintain undifferentiated state and differentiate into specialized cell types. Despite numerous progress has been achieved in understanding stem cell self-renewal and differentiation, many fundamental questions remain unanswered. In this study, we identify dRTEL1, theDrosophilahomolog of Regulator of Telomere Elongation Helicase 1, as a novel regulator of male germline stem cells (GSCs). Our genome-wide transcriptome analysis and ChIP-Seq results suggest that dRTEL1 affects a set of candidate genes required for GSC maintenance, likely independent of its role in DNA repair. Furthermore, dRTEL1 prevents DNA damage-induced checkpoint activation in GSCs. Finally, dRTEL1 functions to sustain Stat92E protein levels, the key player in GSC maintenance. Together, our findings reveal an intrinsic role of the DNA helicase dRTEL1 in maintaining male GSC and provide insight into the function of dRTEL1.

Aedes aegypti (Linnaeus, 1762) is the insect vector that transmits several deadly human diseases. Although the egg stage is an important phase of its life cycle, the biology of mosquito egg remains poorly understood. Here, we report our investigations on the chemical factors that induced hatching of Ae. aegypti eggs. Commercial yeast extracts were able to increase egg hatching rate in a dose-dependent manner, with a hatching rate that ranged from approximately 10% with 1 g/liter to 80% with 20 g/liter of yeast extract. Notably, the addition of glutathione, a reducing agent that showed no significant effect on egg hatching by itself, enhanced and stabilized the activity of yeast extract for at least 70 h. Because dissolved oxygen in different treatments was maintained at high levels in a narrow range (92–95%), we proposed that yeast extract contains hatching inducing compound (HIC) which is able to trigger egg hatching independent of dissolved oxygen level. The HIC in yeast extract could prove to be a potential starting point to design an effective tool to forcefully induce mosquito eggs to hatch under unfavorable conditions, functioning as a novel method for vector control.