Scholarly Literature

This is a database of scholarly literature that concentrates currently on natural and engineered selfish genetic elements (gene drives).  The latest are shown here.
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Gene drives in malaria control: what we need to know

19289
R. Mudziwapasi, M. C. Changara, A. Ndudzo, T. Kaseke, F. Godobo, F. L. Mtemeli, R. Shoko, F. Songwe, S. Ndlovu and S. Sandra Mlambo,  Biotechnology and Biotechnological Equipment,  35:1623-1631. 2021-11-15 13:42:40.
Gene drives are being used to enhance a DNA sequence?s likelihood of passing between generations via sexual reproduction. Gene drives can be deployed to manipulate natural populations. They can be used to suppress populations by reducing the number of individuals in a population or to modify populations. There are more than 3000 mosquito species in the world, some of which are vectors of diseases. Malaria is a typical disease whose vectors are mosquitoes. It affects mostly tropical countries. It kills many people annually, many of whom are children. Interventions currently in use, such as indoor residual spraying and mosquito nets, are proving insufficient to eradicate malaria. Gene drives can be used in different ways to control mosquito populations or to eliminate mosquito species, thereby reducing malaria cases and deaths. This can occur through population replacement or suppression. However, before the elimination of any mosquito species for malaria control, it is necessary to consider the effects of such an action. Additionally, there is a need to review the options available for the control of mosquitoes and to create awareness of the benefits and risks of such an action. This paper, therefore, looks at the role of mosquitoes in the environment, the methods of controlling mosquitoes and malaria and necessary considerations when using gene drives inter alia.

New developments in the field of genomic technologies and their relevance to conservation management

19273
G. Segelbacher, M. Bosse, P. Burger, P. Galbusera, J. A. Godoy, P. Helsen, C. Hvilsom, L. Iacolina, A. Kahric, C. Manfrin, M. Nonic, D. Thizy, I. Tsvetkov, N. Veličković, C. Vilà, S. M. Wisely and E. Buzan,  Conservation Genetics,  2021-11-11 16:22:03.
Recent technological advances in the field of genomics offer conservation managers and practitioners new tools to explore for conservation applications. Many of these tools are well developed and used by other life science fields, while others are still in development. Considering these technological possibilities, choosing the right tool(s) from the toolbox is crucial and can pose a challenging task. With this in mind, we strive to inspire, inform and illuminate managers and practitioners on how conservation efforts can benefit from the current genomic and biotechnological revolution. With inspirational case studies we show how new technologies can help resolve some of the main conservation challenges, while also informing how implementable the different technologies are. We here focus specifically on small population management, highlight the potential for genetic rescue, and discuss the opportunities in the field of gene editing to help with adaptation to changing environments. In addition, we delineate potential applications of gene drives for controlling invasive species. We illuminate that the genomic toolbox offers added benefit to conservation efforts, but also comes with limitations for the use of these novel emerging techniques.

Molecular Mechanisms and Evolutionary Consequences of Spore Killers in Ascomycetes

19237
S. Zanders and H. Johannesson,  Microbiology and Molecular Biology Reviews,  2021-11-10 22:05:58.
In this review, we examine the fungal spore killers. These are meiotic drive elements that cheat during sexual reproduction to increase their transmission into the next generation. Spore killing has been detected in a number of ascomycete genera, including Podospora, Neurospora, Schizosaccharomyces, Bipolaris, and Fusarium. There have been major recent advances in spore killer research that have increased our understanding of the molecular identity, function, and evolutionary history of the known killers. The spore killers vary in the mechanism by which they kill and are divided into killer-target and poison-antidote drivers. In killer-target systems, the drive locus encodes an element that can be described as a killer, while the target is an allele found tightly linked to the drive locus but on the nondriving haplotype. The poison-antidote drive systems encode both a poison and an antidote element within the drive locus. The key to drive in this system is the restricted distribution of the antidote: only the spores that inherit the drive locus receive the antidote and are rescued from the toxicity of the poison. Spore killers also vary in their genome architecture and can consist of a single gene or multiple linked genes. Due to their ability to distort meiosis, spore killers gain a selective advantage at the gene level that allows them to increase in frequency in a population over time, even if they reduce host fitness, and they may have significant impact on genome architecture and macroevolutionary processes such as speciation.

High Temperature Cycles Result in Maternal Transmission and Dengue Infection Differences Between Wolbachia Strains in Aedes aegypti

19221
M. V. Mancini, T. H. Ant, C. S. Herd, J. Martinez, S. M. Murdochy, D. D. Gingell, E. Mararo, P. C. D. Johnson and S. P. Sinkins,  mBio,  e0025021. 2021-11-10 21:39:39.
Environmental factors play a crucial role in the population dynamics of arthropod endosymbionts, and therefore in the deployment of Wolbachia symbionts for the control of dengue arboviruses. The potential of Wolbachia to invade, persist, and block virus transmission depends in part on its intracellular density. Several recent studies have highlighted the importance of larval rearing temperature in modulating Wolbachia densities in adults, suggesting that elevated temperatures can severely impact some strains, while having little effect on others. The effect of a replicated tropical heat cycle on Wolbachia density and levels of virus blocking was assessed using Aedes aegypti lines carrying strains wMel and wAlbB, two Wolbachia strains currently used for dengue control. Impacts on intracellular density, maternal transmission fidelity, and dengue inhibition capacity were observed for wMel. In contrast, wAlbB-carrying Ae. aegypti maintained a relatively constant intracellular density at high temperatures and conserved its capacity to inhibit dengue. Following larval heat treatment, wMel showed a degree of density recovery in aging adults, although this was compromised by elevated air temperatures. IMPORTANCE In the past decades, dengue incidence has dramatically increased all over the world. An emerging dengue control strategy utilizes Aedes aegypti mosquitoes artificially transinfected with the bacterial symbiont Wolbachia, with the ultimate aim of replacing wild mosquito populations. However, the rearing temperature of mosquito larvae is known to impact on some Wolbachia strains. In this study, we compared the effects of a temperature cycle mimicking natural breeding sites in tropical climates on two Wolbachia strains, currently used for open field trials. When choosing the Wolbachia strain to be used in a dengue control program it is important to consider the effects of environmental temperatures on invasiveness and virus inhibition. These results underline the significance of understanding the impact of environmental factors on released mosquitoes, in order to ensure the most efficient strategy for dengue control.

Genetic control of invasive sea lamprey in the Great Lakes

19270
D. Ferreira-Martins, J. Champer, D. W. McCauley, Z. Zhang and M. F. Docker,  Journal of Great Lakes Research,  2021-11-08 16:16:20.
The invasive sea lamprey was a significant factor in the collapse of fish stocks in the Great Lakes, and it continues to threaten the multi-billion-dollar fishing industry. Thus, substantial resources are invested annually on sea lamprey control. Current control strategies have reduced sea lamprey populations by up to 90%, but they are expensive and have some limitations, e.g., lamprey-specific biocides applied to larval habitat impact native lampreys, and physical barriers that block adult lamprey access to spawning habitat impede migration of other fishes. Therefore, genetic control options which offer a theoretically powerful and effective pest control tool are being explored, although they have uncertain sociopolitical support, especially given the need to protect sea lamprey in their native range in Atlantic drainages. Here, we present an overview of genetic approaches with potential for application to sea lamprey control in the Great Lakes. We classify these approaches into two major categories: self-limiting (heritable sex ratio ratchet, Trojan gene, split gene drive) and self-sustaining (gene drive-based sex ratio distortion, homing suppression gene drive, toxin-antidote gene drives, and modification-type gene drives to aid suppression). We describe the technical aspects, challenges, and potential application of each method, focusing on gene drives, a fast-evolving research area that was only a distant option for sea lamprey control in previous reviews. We conclude that, given the risk of undesired spread of deleterious alleles from the Great Lakes, self-limiting genetic control options and confined gene drives will likely be preferred over unconfined gene drive options for sea lamprey control.

Malaria modeling and optimal control using sterile insect technique and insecticide-treated net

19230
L. Cai, L. Bao, L. Rose, J. Summers and W. Ding,  Applicable Analysis,  2021-11-05 21:55:36.
We investigate a malaria transmission model with SEIR (susceptible-exposed-infected-recovered) classes for the human population, SEI (susceptible-exposed-infected) classes for the wild mosquitoes and an additional class for the sterile mosquitoes. The basic reproduction number of the disease transmission is obtained, and a release threshold of the sterile mosquitoes is provided. We formulate an optimal control problem in which the goal is to minimize both the infected human populations and the cost to implement two control strategies: the release of sterile mosquitoes and the usage of insecticide-treated nets to reduce the malaria transmission. Adjoint equations are derived, and the characterization of the optimal controls is established. Finally, we quantify the effectiveness of the two interventions aimed at limiting the spread of malaria transmission. A combination of both strategies leads to more rapid elimination of the wild mosquito population that can suppress malaria transmission. Numerical simulations are provided to illustrate the results.

The supernumerary B chromosome of maize: drive and genomic conflict

19136
J. A. Birchler and H. Yang,  Open Biol,  11:210197. 2021-11-04 14:47:43.
The supernumerary B chromosome of maize is dispensable, containing no vital genes, and thus is variable in number and presence in lines of maize. In order to be maintained in populations, it has a drive mechanism consisting of nondisjunction at the pollen mitosis that produces the two sperm cells, and then the sperm with the two B chromosomes has a preference for fertilizing the egg as opposed to the central cell in the process of double fertilization. The sequence of the B chromosome coupled with B chromosomal aberrations has localized features involved with nondisjunction and preferential fertilization, which are present at the centromeric region. The predicted genes from the sequence have paralogues dispersed across all A chromosomes and have widely different divergence times suggesting that they have transposed to the B chromosome over evolutionary time followed by degradation or have been co-opted for the selfish functions of the supernumerary chromosome.

Temperature-Inducible Precision-Guided Sterile Insect Technique

19268
N. P. Kandul, J. R. Liu and O. S. Akbari,  CRISPR Journal,  14. 2021-11-03 16:11:04.
Releases of sterile males are the gold standard for many insect population control programs, and precise sex sorting to remove females prior to male releases is essential to the success of these operations. To advance traditional methods for scaling the generation of sterile males, we previously described a CRISPR-mediated precision-guided sterile insect technique (pgSIT), in which Cas9 and gRNA strains are genetically crossed to generate sterile males for mass release. While effective at generating F-1 sterile males, pgSIT requires a genetic cross between the two parental strains, which requires maintenance and sexing of two strains in a factory. Therefore, to advance pgSIT further by removing this crossing step, here we describe a next-generation temperature-inducible pgSIT (TI-pgSIT) technology and demonstrate its proof-of-concept in Drosophila melanogaster. Importantly, we were able to develop a true breeding strain for TI-pgSIT that eliminates the requirement for sex sorting-a feature that may help further automate production at scale.

Population replacement gene drive characteristics for malaria elimination in a range of seasonal transmission settings: a modeling study

19134
S. Leung, N. Windbichler, E. Wenger, C. Bever and P. Selvaraj,  bioRxiv,  2021.11.01.466856. 2021-11-03 14:42:23.
Genetically engineering mosquitoes is a promising new vector control strategy to reinvigorate the fight against malaria in Sub-Saharan Africa. Using an agent-based model of malaria transmission with vector genetics, we examine the impacts of releasing population-replacement gene drive mosquitoes on malaria transmission and quantify the gene drive system parameters required to achieve local elimination within a spatially-resolved, seasonal Sahelian setting. We evaluate the performance of two different gene drive systems: "classic" and "integral". Various transmission regimes (low, moderate, and high - corresponding to annual entomological inoculation rates of 10, 30, and 80 infectious bites per person) and other simultaneous interventions, including deployment of insecticide-treated nets (ITNs) and passive healthcare seeking, are also simulated. Local elimination probabilities decreased with pre-existing population target site resistance frequency, increased with transmission-blocking effectiveness of the introduced antiparasitic gene and drive efficiency, and were context dependent with respect to fitness costs associated with the introduced gene. Of the four parameters, transmission-blocking effectiveness may be the most important to focus on for improvements to future gene drive strains because a single release of classic gene drive mosquitoes is likely to locally eliminate malaria in low to moderate transmission settings only when transmission-blocking effectiveness is very high (above approximately 80-90‰). However, simultaneously deploying ITNs and releasing integral rather than classic gene drive mosquitoes significantly boosts elimination probabilities, such that elimination remains highly likely in low to moderate transmission regimes down to transmission-blocking effectiveness values as low as approximately 50‰ and in high transmission regimes with transmission-blocking effectiveness values above approximately 80-90‰. Thus, a single release of currently achievable population replacement gene drive mosquitoes, in combination with traditional forms of vector control, can likely locally eliminate malaria in low to moderate transmission regimes within the Sahel. In a high transmission regime, higher levels of transmission-blocking effectiveness than are currently available may be required.Competing Interest StatementThe authors have declared no competing interest.

Centromere function in asymmetric cell division in Drosophila female and male germline stem cells

19322
A. M. Kochendoerfer, F. Modafferi and E. M. Dunleavy,  Open Biology,  11:210107. 2021-11-03 14:14:53.
The centromere is the constricted chromosomal region required for the correct separation of the genetic material at cell division. The kinetochore protein complex assembles at the centromere and captures microtubules emanating from the centrosome to orchestrate chromosome segregation in mitosis and meiosis. Asymmetric cell division (ACD) is a special type of mitosis that generates two daughter cells with different fates. Epigenetic mechanisms operating at the centromere have been proposed to contribute to ACD. Recent studies have shown that an asymmetric distribution of CENP-A—the centromere-specific histone H3 variant—between sister chromatids can bias chromosome segregation in ACD. In stem cells, this leads to non-random sister chromatid segregation, which can affect cell fate. These findings support the ‘silent sister' hypothesis, according to which the mechanisms of ACD are epigenetically regulated through centromeres. Here, we review the recent data implicating centromeres in ACDs and cell fate in Drosophila melanogaster female and male germline stem cells.

Modeling the efficacy of CRISPR gene drive for schistosomiasis control

19109
R. E. Grewelle, J. Perez-Saez, J. Tycko, E. K. O. Namigai, C. G. Rickards and G. A. De Leo,  bioRxiv,  2021.10.29.466423. 2021-11-01 14:51:40.
CRISPR gene drives could revolutionize the control of infectious diseases by accelerating the spread of engineered traits that limit parasite transmission in wild populations. While much effort has been spent developing gene drives in mosquitoes, gene drive technology in molluscs has received little attention despite the role of freshwater snails as obligate, intermediate hosts of parasitic flukes causing schistosomiasis -- a disease of poverty affecting more than 200 million people worldwide. A successful drive in snails must overcome self-fertilization, which prevents a drive's spread. Simultaneous hermaphroditism is a feature of snails -- distinct from gene drive model organisms -- and is not yet incorporated in gene drive models of disease control. Here we developed a novel population genetic model accounting for snails' sexual and asexual reproduction, susceptibility to parasite infection regulated by multiple alleles, fitness differences between genotypes, and a range of drive characteristics. We then integrated this model with an epidemiological model of schistosomiasis transmission and snail population dynamics. Simulations showed that gene drive establishment can be hindered by a variety of biological and ecological factors, including selfing. However, our model suggests that, under a range of conditions, gene drive mediated immunity in snails could maintain rapid disease reduction achieved by annual chemotherapy treatment of the human population, leading to long-term elimination. These results indicate that gene drives, in coordination with existing public health measures, may become a useful tool to reduce schistosomiasis burden in selected transmission settings with effective CRISPR construct design and close evaluation of the genetic and ecological landscape.Competing Interest StatementJT and EKON were seed funded by the Merck Innovation Cup 2016 for research on schistosomiasis, and previously employed as external consultants to the Global Health Institute of Merck (KGaA) which produces treatments for schistosomiasis. REG and GADL were partially supported by the National Science Foundation's grants DEB-2011179 and ICER-2024383.

Prevalence and molecular characterization of Wolbachia in field-collected Aedes albopictus, Anopheles sinensis, Armigeres subalbatus, Culex pipiens and Cx. tritaeniorhynchus in China

19078
Y. Yang, Y. He, G. Zhu, J. Zhang, Z. Gong, S. Huang, G. Lu, Y. Peng, Y. Meng, X. Hao, C. Wang, J. Sun and S. Shang,  PLOS Neglected Tropical Diseases,  15:e0009911. 2021-10-29 20:41:21.
Wolbachia are maternally transmitted intracellular bacteria that can naturally and artificially infect arthropods and nematodes. Recently, they were applied to control the spread of mosquito-borne pathogens by causing cytoplasmic incompatibility (CI) between germ cells of females and males. The ability of Wolbachia to induce CI is based on the prevalence and polymorphism of Wolbachia in natural populations of mosquitoes. In this study, we screened the natural infection level and diversity of Wolbachia in field-collected mosquitoes from 25 provinces of China based on partial sequence of Wolbachia surface protein (wsp) gene and multilocus sequence typing (MLST). Among the samples, 2489 mosquitoes were captured from 24 provinces between July and September, 2014 and the remaining 1025 mosquitoes were collected month-by-month in Yangzhou, Jiangsu province between September 2013 and August 2014. Our results showed that the presence of Wolbachia was observed in mosquitoes of Aedes albopictus (97.1%, 331/341), Armigeres subalbatus (95.8%, 481/502), Culex pipiens (87.0%, 1525/1752), Cx. tritaeniorhynchus (17.1%, 14/82), but not Anopheles sinensis (n = 88). Phylogenetic analysis indicated that high polymorphism of wsp and MLST loci was observed in Ae. albopictus mosquitoes, while no or low polymorphisms were in Ar. subalbatus and Cx. pipiens mosquitoes. A total of 12 unique mutations of deduced amino acid were identified in the wsp sequences obtained in this study, including four mutations in Wolbachia supergroup A and eight mutations in supergroup B. This study revealed the prevalence and polymorphism of Wolbachia in mosquitoes in large-scale regions of China and will provide some useful information when performing Wolbachia-based mosquito biocontrol strategies in China.

Wolbachia goes to work in the war on mosquitoes

19076
S. Ong,  Nature,  598:S32-s34. 2021-10-29 20:37:48.
There are two approaches to tackling dengue with Wolbachia. The first involves releasing only modified male mosquitoes. Since 2015, this strategy has been successfully adopted in Singapore and Guangzhou, China, and in parts of the United States, such as Miami, Texas and California. Because eggs produced from unmodified females that mate with modified males do not hatch, the number of mosquitoes in the community is greatly reduced. The second approach, used by some cities in Vietnam, Indonesia, Malaysia, Brazil and Australia, among others, involves releasing modified mosquitoes of both sexes. The infected females pass the bacteria to their offspring. Over time (several months to years, depending on characteristics of the release site), the modified mosquitoes replace the native population.

Alternatives for mammal pest control in New Zealand in the context of concerns about 1080 toxicant (sodium fluoroacetate)

19067
B. Warburton, C. Eason, P. Fisher, N. Hancox, B. Hopkins, G. Nugent, S. Ogilvie, T. A. A. Prowse, J. Ross and P. E. Cowan,  New Zealand Journal of Zoology,  43. 2021-10-29 20:19:18.
The ongoing use of 1080 toxin for the control of mammal pests in New Zealand remains highly contentious. Several reviews over the last 25 years identified information gaps and areas of concern, both social and scientific. In this paper these areas of concern are discussed and the extensive scientific and social research that has been undertaken to clarify and address them is reviewed. Although there has been a major national investment in research aimed at finding an alternative to 1080, that has not yet been fully achieved because of low or inconsistent efficacy and/or low cost-effectiveness of alternatives, regulatory difficulties in obtaining approval for aerial delivery of any alternative, and toxic residue concerns. Finding an alternative that has similar efficacy while satisfying the demands for species-selectivity, no residues, and humaneness is a continuing challenge. The most promising prospect appears to be through understanding the genome of the target animals and opportunities for genetic manipulation, either by developing species-specific designer lethal toxicants based on genome mining, or by gene editing to develop non-lethal technologies. Both will require considerable time and funding for research, and considerable effort and engagement to address social and regulatory hurdles.

A decade of stability for wMel Wolbachia in natural Aedes aegypti populations

19080
P. A. Ross, K. L. Robinson, Q. Yang, A. G. Callahan, T. L. Schmidt, J. K. Axford, M. P. Coquilleau, K. M. Staunton, M. Townsend, S. A. Ritchie, M.-J. Lau, X. Gu and A. A. Hoffmann,  bioRxiv,  2021.10.27.466190. 2021-10-28 20:41:44.
Mosquitoes carrying Wolbachia endosymbionts are being released in many countries for arbovirus control. The wMel strain of Wolbachia blocks Aedes-borne virus transmission and can spread throughout mosquito populations by inducing cytoplasmic incompatibility. Aedes aegypti mosquitoes carrying wMel were first released into the field in Cairns, Australia, over a decade ago, and with wider releases have resulted in the near elimination of local dengue transmission. The long-term stability of Wolbachia effects is critical for ongoing disease suppression, requiring tracking of phenotypic and genomic changes in Wolbachia infections following releases. We used a combination of field surveys, phenotypic assessments, and Wolbachia genome sequencing to show that wMel has remained stable in its effects for up to a decade in Australian Ae. aegypti populations. Phenotypic comparisons of wMel-infected and uninfected mosquitoes from near-field and long-term laboratory populations suggest limited changes in the effects of wMel on mosquito fitness. Treating mosquitoes with antibiotics used to cure the wMel infection had limited effects on fitness in the next generation, supporting the use of tetracycline for generating uninfected mosquitoes without off-target effects. wMel has a temporally stable within-host density and continues to induce complete cytoplasmic incompatibility. A comparison of wMel genomes from pre-release (2010) and nine years post-release (2020) populations show few genomic differences and little divergence between release locations, consistent with the lack of phenotypic changes. These results indicate that releases of Wolbachia-infected mosquitoes for population replacement are likely to be effective for many years, but ongoing monitoring remains important to track potential evolutionary changes.Competing Interest StatementThe authors have declared no competing interest.

RNA virome diversity and Wolbachia infection in individual Drosophila simulans flies

19073
A. S. Ortiz-Baez, M. Shi, A. A. Hoffmann and E. C. Holmes,  Journal of General Virology,  102. 2021-10-28 20:29:18.
The endosymbiont bacteria of the genus Wolbachia are associated with multiple mutualistic effects on insect biology, including nutritional and antiviral properties. Members of the genus Wolbachia naturally occur in fly species of the genus Drosophila, providing an operational model host for studying how virome composition may be affected by its presence. Drosophila simulans populations can carry a variety of strains of members of the genus Wolbachia, with the wAu strain associated with strong antiviral protection under experimental conditions. We used D. simulans sampled from the Perth Hills, Western Australia, to investigate the potential virus protective effect of the wAu strain of Wolbachia on individual wild-caught flies. Our data revealed no appreciable variation in virus composition and abundance between individuals infected or uninfected with Wolbachia associated with the presence or absence of wAu. However, it remains unclear whether wAu might affect viral infection and host survival by increasing tolerance rather than inducing complete resistance. These data also provide new insights into the natural virome diversity of D. simulans. Despite the small number of individuals sampled, we identified a repertoire of RNA viruses, including nora virus, galbut virus, thika virus and La Jolla virus, that have been identified in other species of the genus Drosophila. Chaq virus-like sequences associated with galbut virus were also detected. In addition, we identified five novel viruses from the families Reoviridae, Tombusviridae, Mitoviridae and Bunyaviridae. Overall, this study highlights the complex interaction between Wolbachia and RNA virus infections and provides a baseline description of the natural virome of D. simulans.

Containment Practices for Arthropods Modified with Engineered Transgenes Capable of Gene Drive Addendum 1 to the Arthropod Containment Guidelines, Version 3.2

19069
American Committee of Medical Entomology,  Vector-Borne and Zoonotic Diseases,  2021-10-28 20:19:33.
Responsible conduct of research is a cornerstone of rigorous scientific discovery. Institutional committees, independent advisory panels, and expert steering groups are among the frameworks in academia meant to provide guidance and assurances that research activities do not result in harm to the environment, research staff, or public safety. For research involving arthropods of public health importance, several documents currently exist to guide investigators in methodologies to consider for reducing risks from arthropod escape. However, to date, there has been no standardized set of recommendations on containment practices for arthropods modified with engineered transgenes capable of gene drive. This document is meant to serve as a practical reference to fill that gap. Recommendations outlined here address containment considerations when a risk assessment indicates a possibility of establishment of a new arthropod vector species or genetically modified arthropods in the local environment.

Genome Editing Tools and Gene Drives: A Brief Overview (1st ed.).

19295
R. Mudziwapasi, R. Chekera, C. Z. Ncube, I. Shoko, B. Ncube, T. Moyo, J. G. Chimbo, J. Dube, F. F. Mashiri, M. A. Mubani, D. Maruta, C. Chimbo, M. Masuku, R. Shoko, R. P. Nyamusamba and F. N. Jomane,  CRC Press,  2021-10-21 14:20:34.
Genome-editing methods are becoming routine tools for molecular and cell biologists. Such tools include ZFNs, CRISPR, megaTALs and TALENs. These tools are revolutionizing the creation of precisely manipulated genomes to modify the characteristics of organisms or cells. Additionally, gene drives have altered the way we understand inheritance laws. They give us the ability to have total control of the inheritance of traits of choice and importance. This succinct volume summarizes the history, principles and applications – as well as the advantages and disadvantages – of each of these tools and various kinds of gene drives. The book is part of a program to produce books helpful to students and faculties of science at colleges and universities. This volume in the Pocket Guides to Biomedical Sciences series will help demystify these technologies. The book fills the gap between established conventional methods and the novel and exciting newly introduced tools of genome editing and gene drives. It will help young scientists understand the emerging genome-editing tools and gene drives, thereby promoting related research and adoption.

Positive selection and horizontal gene transfer in the genome of a male-killing Wolbachia

19006
T. Hill, R. L. Unckless and J. I. Perlmutter,  Molecular Biology and Evolution,  2021-10-18 15:21:59.
Wolbachia are a genus of widespread bacterial endosymbionts in which some strains can hijack or manipulate arthropod host reproduction. Male killing is one such manipulation in which these maternally transmitted bacteria benefit surviving daughters in part by removing competition with the sons for scarce resources. Despite previous findings of interesting genome features of microbial sex ratio distorters, the population genomics of male-killers remain largely uncharacterized. Here, we uncover several unique features of the genome and population genomics of four Arizonan populations of a male-killing Wolbachia strain, wInn, that infects mushroom-feeding Drosophila innubila. We first compared the wInn genome to other closely related Wolbachia genomes of Drosophila hosts in terms of genome content and confirm that the wInn genome is largely similar in overall gene content to the wMel strain infecting D. melanogaster. However, it also contains many unique genes and repetitive genetic elements that indicate lateral gene transfers between wInn and non-Drosophila eukaryotes. We also find that, in line with literature precedent, genes in the Wolbachia prophage and Octomom regions are under positive selection. Of all the genes under positive selection, many also show evidence of recent horizontal transfer among Wolbachia symbiont genomes. These dynamics of selection and horizontal gene transfer across the genomes of several Wolbachia strains and diverse host species may be important underlying factors in Wolbachia’s success as a male-killer of divergent host species.

Conditional knockdown of transformer in sheep blow fly suggests a role in repression of dosage compensation and potential for population suppression

19004
M. E. Williamson, Y. Yan and M. J. Scott,  PLOS Genetics,  17:e1009792. 2021-10-18 15:15:17.
In the fruit fly Drosophila melanogaster and in the mosquito Anopheles gambiae, a single gene (Sxl in D. melanogaster, fle in A. gambiae) controls the development of female-specific tissues and X chromosome dosage compensation, which is the equalization of X-linked gene products in males and females. In this study we find evidence that the transformer gene is essential for somatic sex differentiation and repression of X chromosome dosage compensation in female sheep blow fly, Lucilia cuprina. In several of the transgenic strains developed, females are transformed into males on diet that lacks tetracycline. Consequently, these strains could be part of a genetic control program of this major pest of sheep in Australia.

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