CRISPR homing gene drives can convert heterozygous cells with one copy of the drive allele into homozygotes, thereby enabling super-Mendelian inheritance. Such a mechanism could be used, for example, to rapidly disseminate a genetic payload in a population, promising effective strategies for the control of vector-borne diseases. However, all CRISPR homing gene drives studied in insects thus far have produced significant quantities of resistance alleles that would limit their spread. In this study, we provide an experimental demonstration that multiplexing of guide RNAs can both significantly increase the drive conversion efficiency and reduce germline resistance rates of a CRISPR homing gene drive in We further show that an autosomal drive can achieve drive conversion in the male germline, with no subsequent formation of resistance alleles in embryos through paternal carryover of Cas9. Finally, we find that the promoter significantly lowers somatic Cas9 expression compared with the promoter, suggesting that provides a superior choice in drive strategies where gene disruption in somatic cells could have fitness costs. Comparison of drive parameters among the different constructs developed in this study and a previous study suggests that, while drive conversion and germline resistance rates are similar between different genomic targets, embryo resistance rates can vary significantly. Taken together, our results mark an important step toward developing effective gene drives capable of functioning in natural populations and provide several possible avenues for further control of resistance rates.

Invasive rodent populations pose a threat to biodiversity across the globe. When confronted with these invaders, native species that evolved independently are often defenseless. CRISPR gene drive systems could provide a solution to this problem by spreading transgenes among invaders that induce population collapse, and could be deployed even where traditional control methods are impractical or prohibitively expensive. Here, we develop a high-fidelity model of an island population of invasive rodents that includes three types of suppression gene drive systems. The individual-based model is spatially explicit, allows for overlapping generations and a fluctuating population size, and includes variables for drive fitness, efficiency, resistance allele formation rate, as well as a variety of ecological parameters. The computational burden of evaluating a model with such a high number of parameters presents a substantial barrier to a comprehensive understanding of its outcome space. We therefore accompany our population model with a meta-model that utilizes supervised machine learning to approximate the outcome space of the underlying model with a high degree of accuracy. This enables us to conduct an exhaustive inquiry of the population model, including variance-based sensitivity analyses using tens of millions of evaluations. Our results suggest that sufficiently capable gene drive systems have the potential to eliminate island populations of rodents under a wide range of demographic assumptions, though only if resistance can be kept to a minimal level. This study highlights the power of supervised machine learning to identify the key parameters and processes that determine the population dynamics of a complex evolutionary system.

CRISPR gene drives can efficiently convert heterozygous cells with one copy of the drive allele into homozygotes, thereby enabling super-Mendelian inheritance. This mechanism could be used, for example, to rapidly disseminate a genetic payload through a population, promising novel strategies for the control of vector-borne diseases. However, all CRISPR gene drives tested have produced significant quantities of resistance alleles that cannot be converted to drive alleles and would likely prevent these drives from spreading in a natural population. In this study, we assessed three strategies for reducing resistance allele formation. First, we directly compared drives with the nanos and vasa promoters, which showed that the vasa drive produced high levels of resistance alleles in somatic cells. This was not observed in the nanos drive. Another strategy was the addition of a second gRNA to the drive, which both significantly increased the drive conversion efficiency and reduced the formation rate of resistance alleles. Finally, to minimize maternal carryover of Cas9, we assessed the performance of an autosomal drive acting in the male germline, and found no subsequent formation of resistance alleles in embryos. Our results mark a step toward developing effective gene drives capable of functioning in natural populations and provide several possible avenues for further reduction of resistance rates.

Invasive rodent populations pose a threat to biodiversity across the globe. When confronted with these new invaders, native species that evolved independently are often defenseless. CRISPR gene drive systems could provide a solution to this problem by spreading transgenes among invaders that induce population collapse. Such systems might be deployed even where traditional control methods are impractical or prohibitively expensive. Here, we develop a high-fidelity model of an island population of invasive rodents that includes three types of suppression gene drive systems. The individual-based model is spatially explicit and allows for overlapping generations and a fluctuating population size. Our model includes variables for drive fitness, efficiency, resistance allele formation rate, as well as a variety of ecological parameters. The computational burden of evaluating a model with such a high number of parameters presents a substantial barrier to a comprehensive understanding of its outcome space. We therefore accompany our population model with a meta-model that utilizes supervised machine learning to approximate the outcome space of the underlying model with a high degree of accuracy. This enables us to conduct an exhaustive inquiry of the population model, including variance-based sensitivity analyses using tens of millions of evaluations. Our results suggest that sufficiently capable gene drive systems have the potential to eliminate island populations of rodents under a wide range of demographic assumptions, but only if resistance can be kept to a minimal level. This study highlights the power of supervised machine learning for identifying the key parameters and processes that determine the population dynamics of a complex evolutionary system.

Since its inception, surgical management of the ulnar collateral ligament (UCL) is fairly standard; however, the invasive, costly, and time-intensive nature of UCL surgery may be restrictive to some athletes. Electronic databases were searched starting from the year 2013 to September 2018. Extracted data included frequencies of (a) return to play (RTP); (b) return to same level of play (RTSP); (c) athlete’s position; (d) complete reconstitution of the UCL; and (e) the location of ligament rupture (proximal or distal). Proportions of success/failure for selected outcomes were calculated. Additionally, an odds ratio (OR) (95% confidence interval [CI]) determined the association between tear location (proximal vs. distal) and nonsurgical success. A total of 169 athletes underwent nonsurgical management of UCL injury in the seven included studies. Sports included baseball, gymnastics, softball, hockey, volleyball, and tennis. Overall, 83% (n = 140) were able to RTP and 72% (n = 121) were able to RTSP. Those with proximal UCL tears had a RTSP rate of 82% (n = 56) compared to 42% (n = 13) of those with a distal tear. Proximal tears were associated with higher rates of successful outcomes in RTP and RTSP (OR = 6.5 [2.5,16.7], p < .001). In baseball, 76% (n = 38) of pitchers were able to RTSP compared to 90% (n = 9) of position players. When visualized using MRI, 96% (n = 22) of athletes had full UCL reconstitution following nonsurgical management. Based on the pooled outcomes of included studies, nonsurgical management of a UCL injury was reasonably successful for RTP and RTSP rates in professional athletes, with a better chance of success for proximal tears compared to distal and incomplete tears compared to complete. The exploratory nature of utilizing nonsurgical management for UCL sprains in athletes, by way of the case series, appears to be fairly well established, but an upgrade in study design is warranted.