A male-biased sex-distorter gene drive for the human malaria vector Anopheles gambiae

Abstract

ex-chromosome drivers are genetic elements that interfere with chromosome segregation during meiosis and are over-represented in progeny 1. In heterogametic sex, they cause an unbalanced male-to-female ratio among offspring, which can potentially lead to population suppression or extinction. Relatively few sex-chromosome drives have been characterized, most likely because they produce an evolutionary conflict with the rest of the genome that selects for autosomal suppressors or resistant sex chromosomes 2,3. Mathematical modeling predicts that a driving sex distorter will spread in a population and, in the absence of resistance, cause eventual collapse 4,5. Population collapse using natural sex-chromosome drives has been reported in laboratory colonies of Drosophila 6,7. In the field, a population crash of the species Drosophila neotestacea was detected in Washington State due to a natural X-chromosome distorter that produced a female-only population 8. Therefore, sex-distorter drives could conceivably be harnessed for invasive pest or vector control 9,10. Although Y drives are less common than X drives, they have been described in Aedes aegypti and Culex pipiens mosquitoes 11,12. Y drives are particularly attractive for mosquito vector control because they can progressively reduce the number of females and hence disease transmission as they spread. In addition, Y drives are likely to be more effective than X drives because they can increase at a greater rate the fraction of heterogametic driving individuals 3-5. Synthetic sex distorters have been generated in A. gambiae mosquitoes by using site-specific nucleases such as I-PpoI or CRISPR-Cas9, which cleave conserved repeated sequences in the mosquito ribosomal DNA gene cluster located exclusively on the X chromosome 13,14. These nucleases, when expressed during spermatozoa development, selectively cleave the X chromosome, thereby favoring the production of Y-bearing gametes and causing a 95% male bias in the progeny 13,14. However, attempts to convert synthetic sex-ratio distorters into Y-chromosome drives have been unsuccessful so far. In most insect species, including A. gambiae, the sex chromosomes are transcriptionally shut down during gametogenesis, a process known as meiotic sex-chromosome inactivation 15,16 , which prevents the transcription of X-shredding nucleases if they are inserted into the Y chromosome (personal observation, A.C. and R.G.). Recently, a gene drive that targeted the dsx gene reached 100% frequency in 7-11 generations and crashed a caged population of 600 mosquitoes without inducing resistance 17. We hypothesized that it might be possible to circumvent meiotic sex-chromosome inactivation by developing an autosomal male-biased sex distorter and coupling sex-ratio distortion with drive. This could result in a quicker impact on disease transmission and a synergistic effect (robustness) between the sex distorter and gene-drive components. Here we report the design and validation of an SDGD to spread the X-chromosome-shredding I-PpoI endonu...

Efficient population modification gene-drive rescue system in the malaria mosquitoAnopheles stephensi

“…In population suppression systems, these alleles are positively selected over the drive allele if this causes loss-of-function of the target site resulting in a fitness disadvantage 9,13 . Therefore, choosing a functionally constrained target site should alleviate the issue of resistance and proved successful in suppression and sex-distorting strategies targeting a highly conversed region of dsx 6,7 . This strategy also can mitigate the effect of resistance in population modification systems, where the effect of functional resistant target sequences on the drive dynamics is dependent on their fitness relative to that of the drive.…”

“…The challenges faced by current programs to eliminate malaria from high-endemic areas 1 have fostered the development of novel control strategies including those based on genetically-modified mosquitoes. These genetic approaches are bolstered by the development of Cas9/guide RNA(Cas9/gRNA)-based gene-drives 2-4 , with pioneering studies demonstrating effective mosquito population suppression [5][6][7] or modification [8][9][10] , the latter aimed at impairing the ability of adult females to transmit the Plasmodium parasites causing the disease.…”

A home and rescue gene drive efficiently spreads and persists in populations

“…These challenges have fostered the development of innovative population control technologies such as Cas9/guideRNA (Cas9/gRNA) homing-based gene drives (HGDs) (Champer et al, 2016;Esvelt et al, 2014) which have been tested in the laboratory for either population modification (Adolfi et al, 2020;Carballar-Lejarazú et al, 2020;Gantz et al, 2015;Li et al, 2020;Pham et al, 2019) to spread desirable traits that can impair the mosquitoes ability to transmit pathogens (e.g. (Buchman et al, 2020(Buchman et al, , 2019Hoermann et al, 2020;Isaacs et al, 2012;Marshall et al, 2019)), or population suppression (Hammond et al, 2016;Kyrou et al, 2018;Simoni et al, 2020) to reduce and eliminate wild disease transmitting populations of mosquitoes. Despite significant progress, HGDs are still an emerging technology that can suffer from the formation of resistance alleles, hindering their efficacy (Adolfi et al, 2020;Carballar-Lejarazú et al, 2020;Gantz et al, 2015;Hammond et al, 2016;Kandul et al, 2019a;Kyrou et al, 2018;Li et al, 2020;Pham et al, 2019;Simoni et al, 2020).…”

“…(Buchman et al, 2020(Buchman et al, , 2019Hoermann et al, 2020;Isaacs et al, 2012;Marshall et al, 2019)), or population suppression (Hammond et al, 2016;Kyrou et al, 2018;Simoni et al, 2020) to reduce and eliminate wild disease transmitting populations of mosquitoes. Despite significant progress, HGDs are still an emerging technology that can suffer from the formation of resistance alleles, hindering their efficacy (Adolfi et al, 2020;Carballar-Lejarazú et al, 2020;Gantz et al, 2015;Hammond et al, 2016;Kandul et al, 2019a;Kyrou et al, 2018;Li et al, 2020;Pham et al, 2019;Simoni et al, 2020).…”

“…This enables the HGD to home, or copy, itself into the recipient allele (Champer et al, 2016;Esvelt et al, 2014) (referred to as homing from hereon). This general design for HGD was quickly adopted, and many HGDs were developed in several insect species (Gantz et al, 2015;Hammond et al, 2016;Kandul et al, 2019a;Kyrou et al, 2018;Li et al, 2020;Simoni et al, 2020). However, it soon became apparent that HGDs unintentionally promote the formation of resistance alleles through mutagenic repair.…”