Combining two genetic sexing strains allows sorting of non-transgenic males for Aedes genetic control

Techniques for Identifying and Sorting Transgenic Mosquito Larvae

Transgenic mosquitoes are used in many aspects of mosquito research. First, they can help answer biological questions to advance scientific knowledge-for example, in the fields of mosquito-pathogen interactions, insect immunity, or olfaction. Second, transgenic technologies may be used to develop much needed novel vector control strategies, such as mosquitoes that are unable to transmit disease or transgenes that sterilize mosquito females to suppress vector populations. Here, we introduce how researchers use various selection markers to screen for transgenic mosquito larvae following a transgenesis experiment. Common procedures include using a binocular fluorescence microscope for initial screening. For higher-throughput screening, a flow cytometer known as Complex Object Parametric Analyzer and Sorter (COPAS) can be used to stabilize transgenic lines through the purification of homozygous individuals or to manage transgene frequency in established transgenic lines. In particular, COPAS sorting allows the production of mosquito larval cultures composed of a mixture of genotypes (control and genetically modified larvae) with the goal of raising both groups of mosquitoes under the same environmental conditions in preparation for a controlled phenotype assessment. It can also be used to produce large populations of male mosquitoes, which should facilitate the development of mosquito control intervention strategies similar to the sterile insect technique (SIT), which aims to release large numbers of sterile males that will mate with and sterilize wild females to suppress mosquito populations. Finally, the utilization of a puromycin resistance marker cassette to screen for transgenic Anopheles larvae is also introduced.

Efficiency assessment of a novel automatic mosquito pupae sex separation system in support of area-wide male-based release strategies

This study provides a comparative analysis of two state-of-the-art automatic mosquito pupae sex sorters currently available: the ORINNO and the WOLBAKI Biotech pupae sex separation systems, which both exploit the sexual size dimorphism of pupae. In Aedes aegypti, the WOLBAKI sex sorter and the ORINNO with a sieve mesh size of 1.050 mm achieved sex separation with female contamination rates below 1%, low pupae mortality rates and high male flight capacity. However, in Ae. albopictus, there was more variability, with female contamination rates above the 1% threshold and pupae mortality reaching 27% when using the ORINNO sorter. On the other hand, the WOLBAKI sorter achieved a male pupae recovery of 47.99 ± 8.81% and 50.91 ± 11.77% in Ae. aegypti and Ae. albopictus, respectively, while the ORINNO sorter with a smaller sieve size achieved male pupae recoveries of 38.08 ± 9.69% and 40.16 ± 2.73% in Ae. aegypti and Ae. albopictus, respectively. This study provides valuable information for researchers and practitioners in the field, assisting in the selection of the most suitable system for mosquito control, management and research programs depending on their specific requirements.

Neofunctionalization driven by positive selection led to the retention of the loqs2 gene encoding an Aedes specific dsRNA binding protein

BACKGROUND

Mosquito borne viruses, such as dengue, Zika, yellow fever and Chikungunya, cause millions of infections every year. These viruses are mostly transmitted by two urban-adapted mosquito species, Aedes aegypti and Aedes albopictus. Although mechanistic understanding remains largely unknown, Aedes mosquitoes may have unique adaptations that lower the impact of viral infection. Recently, we reported the identification of an Aedes specific double-stranded RNA binding protein (dsRBP), named Loqs2, that is involved in the control of infection by dengue and Zika viruses in mosquitoes. Preliminary analyses suggested that the loqs2 gene is a paralog of loquacious (loqs) and r2d2, two co-factors of the RNA interference (RNAi) pathway, a major antiviral mechanism in insects.

RESULTS

Here we analyzed the origin and evolution of loqs2. Our data suggest that loqs2 originated from two independent duplications of the first double-stranded RNA binding domain of loqs that occurred before the origin of the Aedes Stegomyia subgenus, around 31 million years ago. We show that the loqs2 gene is evolving under relaxed purifying selection at a faster pace than loqs, with evidence of neofunctionalization driven by positive selection. Accordingly, we observed that Loqs2 is localized mainly in the nucleus, different from R2D2 and both isoforms of Loqs that are cytoplasmic. In contrast to r2d2 and loqs, loqs2 expression is stage- and tissue-specific, restricted mostly to reproductive tissues in adult Ae. aegypti and Ae. albopictus. Transgenic mosquitoes engineered to express loqs2 ubiquitously undergo developmental arrest at larval stages that correlates with massive dysregulation of gene expression without major effects on microRNAs or other endogenous small RNAs, classically associated with RNA interference.

CONCLUSIONS

Our results uncover the peculiar origin and neofunctionalization of loqs2 driven by positive selection. This study shows an example of unique adaptations in Aedes mosquitoes that could ultimately help explain their effectiveness as virus vectors.