Comprehensive characterization of a transgene insertion in a highly repetitive, centromeric region of Anopheles mosquitoes

The availability of the genomic sequence of the malaria mosquito Anopheles gambiae has in recent years sparked the development of transgenic technologies with the potential to be used as novel vector control tools. These technologies rely on genome editing that confer traits able to affect vectorial capacity. This can be achieved by either reducing the mosquito population or by making mosquitoes refractory to the parasite infection. For any genetically modified organism that is regarded for release, molecular characterization of the transgene and flanking sites are essential for their safety assessment and post-release monitoring. Despite great advancements, Whole-Genome Sequencing data are still subject to limitations due to the presence of repetitive and unannotated DNA sequences. Faced with this challenge, we describe a number of techniques that were used to identify the genomic location of a transgene in the male bias mosquito strain Ag(PMB)1 considered for potential field application. While the initial inverse PCR identified the most likely insertion site on Chromosome 3 R 36D, reassessment of the data showed a high repetitiveness in those sequences and multiple genomic locations as potential insertion sites of the transgene. Here we used a combination of DNA sequencing analysis and in-situ hybridization to clearly identify the integration of the transgene in a poorly annotated centromeric region of Chromosome 2 R 19D. This study emphasizes the need for accuracy in sequencing data for the genome of organisms of medical importance such as Anopheles mosquitoes and other tools available that can support genomic locations of transgenes.

Resistance to a CRISPR-based gene drive at an evolutionarily conserved site is revealed by mimicking genotype fixation

CRISPR-based homing gene drives can be designed to disrupt essential genes whilst biasing their own inheritance, leading to suppression of mosquito populations in the laboratory. This class of gene drives relies on CRISPR-Cas9 cleavage of a target sequence and copying ('homing') therein of the gene drive element from the homologous chromosome. However, target site mutations that are resistant to cleavage yet maintain the function of the essential gene are expected to be strongly selected for. Targeting functionally constrained regions where mutations are not easily tolerated should lower the probability of resistance. Evolutionary conservation at the sequence level is often a reliable indicator of functional constraint, though the actual level of underlying constraint between one conserved sequence and another can vary widely. Here we generated a novel adult lethal gene drive (ALGD) in the malaria vector Anopheles gambiae, targeting an ultra-conserved target site in a haplosufficient essential gene (AGAP029113) required during mosquito development, which fulfils many of the criteria for the target of a population suppression gene drive. We then designed a selection regime to experimentally assess the likelihood of generation and subsequent selection of gene drive resistant mutations at its target site. We simulated, in a caged population, a scenario where the gene drive was approaching fixation, where selection for resistance is expected to be strongest. Continuous sampling of the target locus revealed that a single, restorative, in-frame nucleotide substitution was selected. Our findings show that ultra-conservation alone need not be predictive of a site that is refractory to target site resistance. Our strategy to evaluate resistance in vivo could help to validate candidate gene drive targets for their resilience to resistance and help to improve predictions of the invasion dynamics of gene drives in field populations.

Cellular mechanisms regulating synthetic sex ratio distortion in the Anopheles gambiae germline

Genetic control strategies aimed to bias the sex of progenies towards males present a promising new paradigm to eliminate malaria-transmitting mosquitoes. A synthetic sex-ratio distortion (SD) system was successfully engineered in Anopheles gambiae by exploiting the meiotic activity of the I-PpoI endonuclease targeting ribosomal DNA (rDNA) repeats, exclusively located on the X chromosome. Males carrying the SD construct produce highly male-biased progenies without evident reduction in fertility. In this study, we investigated the fate of X and Y chromosomes in these SD males and found that ratios of mature X:Y-bearing sperm were comparable to wild-type insects, indicating absence of selection mechanisms during sperm maturation. We therefore tested the effect of meiotic cleavage of both X and Y chromosomes in a lab-generated SD strain carrying rDNA on both sex chromosomes, showing fertility comparable to wild-type and a reduced male-bias compared to SD males in which only the X is targeted. Exposure of Y-linked rDNA to I-PpoI cleavage for consecutive generations rapidly restored the male-bias to typical high frequencies, indicating a correlation between the number of cleavable targets in each sex chromosome and the sex-ratios found in the progeny. Altogether our results indicate that meiotic cleavage of rDNA repeats, located in the sex chromosomes of A. gambiae SD males, affects the competitiveness of mature sperm to fertilize the female oocyte, thereby generating sex-biased progenies. We also show that the presence of rDNA copies on the Y chromosome does not impair the effectiveness of engineered synthetic SD systems for the control of human malaria mosquitoes.

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

Only female insects transmit diseases such as malaria, dengue and Zika; therefore, control methods that bias the sex ratio of insect offspring have long been sought. Genetic elements such as sex-chromosome drives can distort sex ratios to produce unisex populations that eventually collapse, but the underlying molecular mechanisms are unknown. We report a male-biased sex-distorter gene drive (SDGD) in the human malaria vector Anopheles gambiae. We induced super-Mendelian inheritance of the X-chromosome-shredding I-PpoI nuclease by coupling this to a CRISPR-based gene drive inserted into a conserved sequence of the doublesex (dsx) gene. In modeling of invasion dynamics, SDGD was predicted to have a quicker impact on female mosquito populations than previously developed gene drives targeting female fertility. The SDGD at the dsx locus led to a male-only population from a 2.5% starting allelic frequency in 10–14 generations, with population collapse and no selection for resistance. Our results support the use of SDGD for malaria vector control.

A sex-distorter gene drive causes population collapse in the malaria mosquito.

[Initial epidemiological data on the clinical effects in health workers employed in the manual lifting of patients in wards]

An investigation was carried out by teams from various centres coordinated by the EPM (Ergonomics of Posture and Movement) Research Unit on 54 different hospitals in various regions of northern and central Italy. The teams examined a total of 3341 health workers whose job involved manual handling of patients (553 male and 2788 females, 1568 working in hospitals and 1773 in geriatric residences). Numerous meetings were held to ensure that the methods of assessing the exposure indexes and spinal impairment were identical in the various teams. The final data were processed centrally at the EPM Research Unit. The sample analyzed may be considered as representative of the situation in hospitals in Italy, at least for northern and central Italy. The mean age was 36 years, mean length of service in the department 6 years and mean length of job duration not exceeding 10 years; staff turnover was high. Physical examination revealed that 8.4% of the workers had had at least one episode of acute low back pain in the previous 12 months: i.e., 4 times the values of the reference groups. Also in the case of clinical-functional spondyloarthropathies of the lumbosacral spine, in the females there was a significantly higher prevalence than in the reference groups. All disorders were more severe in sectors more at risk, i.e., old peoples homes, rehabilitation centres, orthopaedic and surgical departments, and in any case higher in old peoples homes and geriatric residences. The initial data concerning the ratio between presence of spinal disease and risk index were also positive.

[The prevention of risk due to the manual lifting of patients: the psychosocial component]

A high percentage of musculoskeletal disorders in nursing staff with the task of patient lifting is reported in the literature. These disorders are considered to be of multiple etiology and attempts have been made not only to assess the physical load but also to identify the direct or indirect influence of organisational and psychosocial factors so that preventive measures be more appropriate and effective (Law 626/94). In this context, in a recent publication NIOSH recalled that psychosocial factors can alter the relationship between exposure to physical loads and the development or the prognosis of these disorders, and stresses that understanding these relationships is the crucial factor in assessment of exposure that can be addressed with preventive and therapeutic measures. A study was carried out on the staff (113 subjects) of a large hospital in northern Italy with departments recognised by certified occupational physicians as at risk for the musculoskeletal apparatus. In order to quantify the working conditions and the disorders of the spine, a protocol proposed by the Ergonomics of Posture and Movement Research Unit of Milan University was further developed and validated. For assessment of psychosocial factors an Italian version of R. A. Karasek's "Job Content Questionnaire" was drawn up and validated by the Centre for Study and Research of Chronic Degenerative Diseases in Working Environments of Milan University. In addition, Borg's Scale was used for perception of physical load, Kurimori and Kakizaki's Scale for mental fatigue, Kjellberg and Iwanowski's Scale for states of stress, plus the Maslach burnout inventory. Nonparametric statistical analysis was applied to determine the influence of physical and organisational and psychosocial factors on disorders of the musculoskeletal apparatus. The results confirm a good agreement between the objective and subjective assessments of "manual patient handling" risk (Kendall p from 0.26 to 0.37, p > 0.001) and the significant relationships between psychosocial factors and disorders of the lumbar region of the spine: past history of episodes of acute low back pain is associated with limited possibility of making independent decisions (U-Mann Whitney z = 2.81, p 0.004) and job insecurity (U-Mann Whitney z = -2.36, p 0.01); episodes of acute low back pain above the threshold in the previous year were associated with low discretionary powers at work. The results will be discussed on the basis of the possible prevention measures.

Hemimegalencephaly, hemihypertrophy and vascular lesions

We report on two children with hemihypertrophy and ipsilateral hemimegalencephaly. Vascular lesions in one were consistent with a diagnosis of the Klippel-Trénaunay-Weber Syndrome. MRI performed in the first days of life and at 1 month of age revealed the presence of the neuronal anomaly.

CONCLUSION

The occurrence of hemimegalencephaly in our patients indicates that hemihypertrophy and vascular dysplasia are pathogenetically related phenomena of a continuous spectrum in which this brain disorder may appear.