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Targeted DNA sequencing approaches will improve how the size of short tandem repeats is measured for diagnostic tests and preclinical studies. The expansion of these sequences causes dozens of disorders, with longer tracts generally leading to a more severe disease. Interrupted alleles are sometimes present within repeats and can alter disease manifestation. Determining repeat size mosaicism and identifying interruptions in targeted sequencing datasets remains a major challenge. This is in part because standard alignment tools are ill-suited for repetitive and unstable sequences. To address this, we have developed Repeat Detector (RD), a deterministic profile weighting algorithm for counting repeats in targeted sequencing data. We tested RD using blood-derived DNA samples from Huntington’s disease and Fuchs endothelial corneal dystrophy patients sequenced using either Illumina MiSeq or Pacific Biosciences single-molecule, real-time sequencing platforms. RD was highly accurate in determining repeat sizes of 609 blood-derived samples from Huntington’s disease individuals and did not require prior knowledge of the flanking sequences. Furthermore, RD can be used to identify alleles with interruptions and provide a measure of repeat instability within an individual. RD is therefore highly versatile and may find applications in the diagnosis of expanded repeat disorders and in the development of novel therapies.

Background:\ud Huntington’s disease (HD) is an autosomal dominant neurodegenerative disorder caused by the expansion of the HTT CAG repeat. Affected individuals inherit ≥36 repeats and longer alleles cause earlier onset, greater disease severity and faster disease progression. The HTT CAG repeat is genetically unstable in the soma in a process that preferentially generates somatic expansions, the proportion of which is associated with disease onset, severity and progression. Somatic mosaicism of the HTT CAG repeat has traditionally been assessed by semi-quantitative PCR-electrophoresis approaches that have limitations (e.g., no information about sequence variants). Genotyping-by-sequencing could allow for some of these limitations to be overcome.\ud \ud Objective:\ud To investigate the utility of PCR sequencing to genotype large (>50 CAGs) HD alleles and to quantify the associated somatic mosaicism.\ud \ud Methods:\ud We have applied MiSeq and PacBio sequencing to PCR products of the HTT CAG repeat in transgenic R6/2 mice carrying ∼55, ∼110, ∼255 and ∼470 CAGs. For each of these alleles, we compared the repeat length distributions generated for different tissues at two ages.\ud \ud Results:\ud We were able to sequence the CAG repeat full length in all samples. However, the repeat length distributions for samples with ∼470 CAGs were biased towards shorter repeat lengths.\ud \ud Conclusion:\ud PCR sequencing can be used to sequence all the HD alleles considered, but this approach cannot be used to estimate modal allele size or quantify somatic expansions for alleles ⪢250 CAGs. We review the limitations of PCR sequencing and alternative approaches that may allow the quantification of somatic contractions and very large somatic expansions.

We aimed to determine the genetic diversity and molecular characteristics of the Huntington disease (HD) gene (HTT) in Spain. We performed an extended haplotype and exon one deep sequencing analysis of the HTT gene in a nationwide cohort of population-based controls (n = 520) and families with symptomatic individuals referred for HD genetic testing. This group included 331 HD cases and 140 carriers of intermediate alleles. Clinical and family history data were obtained when available. Spanish normal alleles are enriched in C haplotypes (40.1%), whereas A1 (39.8%) and A2 (31.6%) prevail among intermediate and expanded alleles, respectively. Alleles ≥ 50 CAG repeats are primarily associated with haplotypes A2 (38.9%) and C (32%), which are also present in 50% and 21.4%, respectively, of HD families with large intergenerational expansions. Non-canonical variants of exon one sequence are less frequent, but much more diverse, in alleles of ≥27 CAG repeats. The deletion of CAACAG, one of the six rare variants not observed among smaller normal alleles, is associated with haplotype C and appears to correlate with larger intergenerational expansions and early onset of symptoms. Spanish HD haplotypes are characterized by a high genetic diversity, potentially admixed with other non-Caucasian populations, with a higher representation of A2 and C haplotypes than most European populations. Differences in haplotype distributions across the CAG length range support differential germline expansion dynamics, with A2 and C showing the largest intergenerational expansions. This haplotype-dependent germline instability may be driven by specific cis-elements, such as the CAACAG deletion. This study was funded by the Instituto de Salud Carlos III (grant no. FIS PI15/02227), and the CHDI Foundation (Enroll -HD study). A. Ruiz de Sabando was supported by a Fellowship of Departamento de Salud, Gobierno de Navarra (ref. 0011-4809-2018-000001).

Huntington’s disease (HD) is an inherited neurodegenerative disorder caused by an expanded CAG repeat in the HTT gene. It is diagnosed following a standardized exam of motor control and often presents with cognitive decline and psychiatric symptoms. Recent studies have detected genetic loci modifying the age at onset of motor symptoms in HD, but genetic factors influencing cognitive and psychiatric presentations are unknown. We tested the hypothesis that psychiatric and cognitive symptoms in HD are influenced by the same common genetic variation as in the general population by constructing polygenic risk scores from large genome-wide association studies of psychiatric and neurodegenerative disorders, and of intelligence, and testing for correlation with the presence of psychiatric and cognitive symptoms in a large sample (n=5160) of HD patients. Polygenic risk score for major depression was associated specifically with increased risk of depression in HD, as was schizophrenia risk score with psychosis and irritability. Cognitive impairment and apathy were associated with reduced polygenic risk score for intelligence. In general, polygenic risk scores for psychiatric disorders, particularly depression and schizophrenia, are associated with increased risk of the corresponding psychiatric symptoms in HD, suggesting a common genetic liability. However, the genetic liability to cognitive impairment and apathy appears to be distinct from other psychiatric symptoms in HD. No associations were observed between HD symptoms and risk scores for other neurodegenerative disorders. These data provide a rationale for treatments effective in depression and schizophrenia to be used to treat depression and psychotic symptoms in HD.

Genome-wide association studies (GWAS) of Huntington’s disease (HD) have identified six DNA maintenance gene loci (among others) as modifiers and implicated a two step-mechanism of pathogenesis: somatic instability of the causative HTT CAG repeat with subsequent triggering of neuronal damage. The largest studies have been limited to HD individuals with a rater-estimated age at motor onset. To capitalize on the wealth of phenotypic data in several large HD natural history studies, we have performed algorithmic prediction using common motor and cognitive measures to predict age at other disease landmarks as additional phenotypes for GWAS. Combined with imputation using the Trans-Omics for Precision Medicine reference panel, predictions using integrated measures provided objective landmark phenotypes with greater power to detect most modifier loci. Importantly, substantial differences in the relative modifier signal across loci, highlighted by comparing common modifiers at MSH3 and FAN1, revealed that individual modifier effects can act preferentially in the motor or cognitive domains. Individual components of the DNA maintenance modifier mechanisms may therefore act differentially on the neuronal circuits underlying the corresponding clinical measures. In addition, we identified new modifier effects at the PMS1 and PMS2 loci and implicated a potential new locus on chromosome 7. These findings indicate that broadened discovery and characterization of HD genetic modifiers based on additional quantitative or qualitative phenotypes offers not only the promise of in-human validated therapeutic targets, but also a route to dissecting the mechanisms and cell types involved in both the somatic instability and toxicity components of HD pathogenesis.

Huntington disease (HD)is a dominantly inherited neurodegenerative disorder caused by the expansion of a polyglutamine encoding CAG repeat in the huntingtin gene. Recently, it has been established that disease severity in HD is best predicted by the number of pure CAG repeats rather than total glutamines encoded. Along with uncovering DNA repair gene variants as

SummaryThe age at onset of motor symptoms in Huntington’s disease (HD) is driven by HTT CAG repeat length but modified by other genes. We used exome sequencing of 683 HD patients with extremes of onset or phenotype relative to CAG length to identify rare variants associated with clinical effect. We identified damaging coding variants in candidate modifier genes from prior genome-wide association studies associated with altered HD onset or severity. Variants in FAN1 clustered in its DNA-binding and nuclease domains and were associated predominantly with earlier onset HD. Nuclease activities of these variants correlated with residual age at motor onset of HD. Mutating endogenous FAN1 to a nuclease-inactive form in an induced pluripotent stem cell model of HD led to rates of CAG expansion comparable to those observed with complete FAN1 knock out. Together, these data implicate FAN1 nuclease activity in slowing somatic repeat expansion and hence onset of HD.

Background: Huntington’s disease (HD) is caused by an expanded (>35) CAG trinucleotide repeat in huntingtin (HTT). Age-at-onset of motor symptoms is inversely correlated with the size of the inherited CAG repeat, which expands further in brain regions due to somatic repeat instability. Our recent genetic investigation focusing on autosomal SNPs revealed that age-at-onset is also influenced by genetic variation at many loci, the majority of which encode genes involved in DNA maintenance/repair processes and repeat instability. Objective: We performed a complementary association analysis to determine whether variants in the X chromosome modify HD. Methods: We imputed SNPs on chromosome X for ∼9,000 HD subjects of European ancestry and performed an X chromosome-wide association study (XWAS) to test for association with age-at-onset corrected for inherited CAG repeat length. Results: In a mixed effects model XWAS analysis of all subjects (males and females), assuming random X-inactivation in females, no genome-wide significant onset modification signal was found. However, suggestive significant association signals were detected at Xq12 (top SNP, rs59098970; p-value, 1.4E-6), near moesin (MSN), in a region devoid of DNA maintenance genes. Additional suggestive signals not involving DNA repair genes were observed in male- and female-only analyses at other locations. Conclusion: Although not genome-wide significant, potentially due to small effect size compared to the power of the current study, our data leave open the possibility of modification of HD by a non-DNA repair process. Our XWAS results are publicly available at the updated GEM EURO 9K website hosted at https://www.hdinhd.org/ for browsing, pathway analysis, and data download.

Although Huntington’s disease (HD) is a well studied Mendelian genetic disorder, less is known about its associated epigenetic changes. Here, we characterize DNA methylation levels in six different tissues from 3 species: a mouse huntingtin (Htt) gene knock-in model, a transgenic HTT sheep model, and humans. Our epigenome-wide association study (EWAS) of human blood reveals that HD mutation status is significantly (p, Although Huntington’s disease (HD) is a well-studied genetic disorder, less is known about the epigenetic changes underlying it. Here, the authors characterize DNA methylation levels in tissues from patients, a mouse huntingtin (Htt) gene knock-in model, and a transgenic HTT sheep model, and provide evidence that HD is accompanied by DNA methylation changes in these three species.

Background: Changes in climate and land use can alter risk of transmission of parasites between domestic hosts and wildlife, particularly when mediated by vectors that can travel between populations. Here we focused on tsetse flies (genus Glossina), the cyclical vectors for both Human African Trypanosomiasis (HAT) and Animal African Trypanosomiasis (AAT). The aims of this study were to investigate three issues related to G. palldipes from Kenya: 1) the diversity of vertebrate hosts that flies fed on; 2) whether host feeding patterns varied in relation to type of hosts, tsetse feeding behaviour, site or tsetse age and sex; and 3) if there was a relationship between trypanosome detection and host feeding behaviours or host types. Methods: Sources of blood meals of Glossina pallidipes were identified by sequencing of the mitochondrial cytochrome b gene and analyzed in relationship with previously determined trypanosome detection in the same flies. Results: In an area dominated by wildlife but with seasonal presence of livestock (Nguruman), 98% of tsetse fed on single wild host species, whereas in an area including a mixture of resident domesticated animals, humans and wildlife (Shimba Hills), 52% of flies fed on more than one host species. Multiple Correspondence Analysis revealed strong correlations between feeding pattern, host type and site but these were resolved along a different dimension than trypanosome status, sex and age of the flies. Conclusions: Our results suggest that individual G. pallidipes in interface areas may show higher feeding success on wild hosts when available but often feed on both wild and domesticated hosts. This illustrates the importance of G. pallidipes as a vector connecting the sylvatic and domestic cycles of African trypanosomes.

Stingless bees are important pollinators of wild plants and crops. The identity of stingless bee species in Africa has not been fully documented. The present study explored the utility of morphometrics and DNA barcoding for identification of African stingless bee populations, and to further employ these tools to identify potential cryptic variation within species. Stingless bee samples were collected from three ecological zones, namely Kakamega Forest, Mwingi and Arabuko-Sokoke Forest, which are geographically distant and cover high, medium and low altitudes, respectively. Forewing and hind leg morphometric characters were measured to determine the extent of morphological variation between the populations. DNA barcodes were generated from the mitochondrial cytochrome c-oxidase I (COI) gene. Principal Component Analysis (PCA) on the morphometric measurements separated the bee samples into three clusters: (1) Meliponula bocandei; (2) Meliponula lendliana + Plebeina hildebrandti; (3) Dactylurina schmidti + Meliponula ferruginea black + Meliponula ferruginea reddish brown, but Canonical Variate Analysis (CVA) separated all the species except the two morphospecies (M. ferruginea reddish brown and black). The analysis of the COI sequences showed that DNA barcoding can be used to identify all the species studied and revealed remarkable genetic distance (7.3%) between the two M. ferruginea morphs. This is the first genetic evidence that M. ferruginea black and M. ferruginea reddish brown are separate species.

Huntington disease \(HD) is an autosomal dominant neurodegenerative disorder caused by the expansion of a CAG repeat in the first exon of the _HTT_ gene. Affected individuals inherit more than 40 repeats and the CAG repeat is genetically unstable in both the germline and soma. Molecular diagnosis and genotyping of the CAG repeat is traditionally performed by estimation of PCR fragment size. However, this approach is complicated by the presence of an adjacent polymorphic CCG repeat and provides no information on the presence of variant repeats, flanking sequence variants or on the degree of somatic mosaicism. To overcome these limitations, we have developed an amplicon-sequencing protocol that allows the sequencing of hundreds of samples in a single MiSeq run. The composition of the _HTT_ exon one trinucleotide repeat locus can be determined from the MiSeq sequencing reads generated. With sufficient sequencing depth, such MiSeq data can also be used to quantify the degree of somatic mosaicism of the _HTT_ CAG repeat in the tissue analysed.

SUMMARYThe effects of variable, glutamine-encoding, CAA interruptions indicate that a property of the uninterrupted HTT CAG repeat sequence, distinct from huntingtin’s polyglutamine segment, dictates the rate at which HD develops. The timing of onset shows no significant association with HTT cis-eQTLs but is influenced, sometimes in a sex-specific manner, by polymorphic variation at multiple DNA maintenance genes, suggesting that the special onset-determining property of the uninterrupted CAG repeat is a propensity for length instability that leads to its somatic expansion. Additional naturally-occurring genetic modifier loci, defined by GWAS, may influence HD pathogenesis through other mechanisms. These findings have profound implications for the pathogenesis of HD and other repeat diseases and question a fundamental premise of the “polyglutamine disorders”.

Background: Huntington disease (HD) is a dominantly inherited neurodegenerative disorder, presenting with a movement disorder, cognitive decline and psychiatric complications. HD is caused by the expansion of a CAG repeat tract in exon 1 of the huntingtin gene (HTT). In other repeat expansion disorders, variants within the associated repeat tracts may affect stability, which in turn modifies disease severity. Although sequence variation has been reported within the sequence encoding the HTT polyglutamine and polyproline tract, little is known about its effect on disease. Aim: To determine the sequence diversity precisely within the HTT exon 1 trinucleotide repeat in black South African individuals and assess the effect of sequence variation in modifying disease. Methods/techniques: A sample of black South African individuals (59 patients and 153 controls) was analysed using a specialised high-throughput DNA sequencing assay and data analysis pipeline, specific for the HTT exon 1 repeat. Results/outcomes: Significant diversity was observed in comparison to a European sample of patients, with novel African alleles defined by the description of allele sub-structures. The most common disease allele structure in our patients was associated with the absence of the CCGCCA cassette that precedes the polyproline CCG repeat in typical HD-causing alleles. Regression analysis determined that age at diagnosis was approximately 6 to 13 years earlier in patients carrying HD-causing alleles lacking the CCGCCA cassette. Conclusion: This is the first study to describe allele sequence diversity within the HTT exon 1 repeat in an African population. The absence of the CCGCCA cassette, which appears to be African-specific and associated with an earlier age at diagnosis in African HD patients, is a potential cis-acting modifier of HD onset.

Background Huntington disease (HD) is caused by the expansion of a polyglutamine encoding CAG repeat in exon 1 of the HTT gene. Affected individuals inherit ≥40 repeats and longer alleles are associated with earlier onset and higher HD severity. The HTT CAG repeat is genetically unstable in both the germline and soma. Somatic mosaicism is dependent on the number of CAG repeats and age, and is expansion biased and cell-type specific. Recent genome-wide association studies (GWAS) have identified components of the DNA repair system as trans¬-acting modifiers of HD severity, some of which are known to modify somatic instability of the HTT CAG repeat in HD mouse models. We thus hypothesise that the trans¬-acting modifiers identified by GWAS affect HD severity by their direct effect on HTT CAG somatic instability. Aims Determine the exact trinucleotide structure of the HTT exon 1 repeat and quantify its somatic mosaicism to investigate their association with HD severity. Methods/techniques Using genotyping-by-sequencing, we determined the exact genotype of the polyglutamine and polyproline encoding repeats in HTT exon 1 and quantified the somatic mosaicism associated with the CAG repeat in blood DNA from 807 HD expansion carriers. Results/outcome The sequence encoding the HTT polyglutamine and polyproline tract has an atypical structure in ˜8% of the non-HD-causing alleles and ˜3% of the HD-causing alleles, differing from the typical structure by the number of glutamine encoding CAA codons and/or the number of proline encoding CCA and CCT codons. Multiple linear regression analysis revealed that the number of CAA codons is negatively correlated with HD severity and that the number of CAG repeats is a better predictor of HD severity (r2=0.559) than the number of glutamines (r2=0.537). Moreover, somatic mosaicism in blood correlates with HD severity (r2 ≥0.014, p≤2.5 × 10–3) and some of the polymorphisms associated with HD severity (p=1.5 × 10–5 for FAN1 rs3512, p=1.8 × 10–4 for MLH3 rs175080, p=3.6 × 10–3 for MLH1 rs1799977 and p=0.016 for MSH3 rs1382539). Conclusion Our data show that atypical HD-causing alleles have major implications for genetic diagnosis and counselling and confirm the correlation of somatic expansion with HD severity. The latter further supports the therapeutic potential of targeting expansion causing components of the DNA repair system.

Background Huntington’s Disease (HD) is fully penetrant when ≥40 CAG repeats are present in the Huntingtin gene. CAG repeat length is inconsistent both between and within germline and somatic tissues, and this instability is most evident in the brain. Such somatic expansions are suggested to contribute to HD progression and neurodegeneration. It has been determined in a small number of Vonsattel grade 0 HD cases that neuronal CAG repeat expansions are more prominent in the striatum than in the cortex. As the disease progresses, this association is reversed. However, the very large expansions previously reported have not been replicated. Aims To determine the exact CAG repeat sequence and length in six post-mortem human HD brains and corresponding blood, and examine the tissue-specific pattern of somatic mosaicism. Methods DNA was extracted from brain and blood, sized by fragment analysis, cloned and sequenced by Sanger sequencing, Illumina MiSeq, and PacBio SMRT sequencing. Small-pool PCR was used for repeat length quantification. Results Large expansions up to 620 CAG repeats are present in end-stage HD human post-mortem brains. The association between the striatum and cortex in relation to the degree of mosaicism is dependent on patient phenotype. With the exception of one sample, the cerebellum and blood are consistently stable. Conclusions Repeat expansions up to 15x the diagnostically sized expanded allele are present in the post-mortem human HD brain, substantiating the extent of the tissue-specific instability observed and consistent with a major role in driving disease pathology.

Background: Huntington’s disease (HD) and myotonic dystrophy type 1 (DM1) are dominantly inherited diseases caused respectively by CAG and CTG repeat expansions. In both, inherited repeat length correlates positively with severity and negatively with onset. Expanded repeats are unstable through the germline, and somatically, likely contributing to onset and progression. Genetic: variation in MSH3, a DNA mismatch repair protein, is associated with slower HD progression and a lower rate of somatic expansion in DM1. The lead SNP in a GWAS of HD progression, rs557874766, is located in a polymorphic 9 bp tandem repeat in MSH3 exon 1. Msh3 inactivation in animal models of HD and DM1 is known to prevent repeat expansion and ameliorate disease phenotype. Aim: Determine the exact genotype of the MSH3 exon 1 repeat and conduct genotype-phenotype analysis in HD and DM1. Methods/techniques: We conducted next-generation sequencing of the MSH3 repeat region in cohorts of 218 HD and 200 DM1 patients. RNA-Seq was used to quantify whole blood MSH3 expression in HD subjects. In a transcriptome-wide association study (TWAS), MSH3 expression from human prefrontal cortex was imputed into HD GWAS data. Results/outcome: Rs557874766 was found to be an alignment artefact due to the sequence complexity of varying numbers of 9 bp tandem repeats. Individuals who appeared to have the rs557874766 minor allele, associated with delayed HD onset, had a three-repeat variant (allele frequency 26%). Fourteen MSH3 repeat alleles were observed, with the commonest containing six repeats and corresponding to the reference sequence. Each copy of the three-repeat allele slows HD progression by 0.34 UHDRS motor units and 0.1 functional capacity units per year (p=2.18E-7), and delays onset by 2.08 years (p=0.037). In DM1 each three-repeat allele correlates with a lower rate of somatic expansion (p=0.02) and later age of onset (p=0.04). Three-repeat homozygotes had significantly lower MSH3 expression in blood (p=0.028). The TWAS identified significant association of decreased MSH3 with slow progression (p=2.52E-6). Conclusion: A three-repeat variant in MSH3 exon 1 is associated with reduced MSH3 expression and slower progression in HD, reduced rate of somatic expansion in DM1 and delayed onset in both diseases. Genetic variation reducing MSH3 expression may reduce somatic expansion, delay onset and slow progression. Therapies reducing MSH3 could ameliorate several repeat expansion diseases.

Biting flies of the family Tabanidae are important vectors of human and animal diseases across continents. However, records of Africa tabanids are fragmentary and mostly cursory. To improve identification, documentation and description of Tabanidae in East Africa, a baseline survey for the identification and description of Tabanidae in three eastern African countries was conducted. Tabanids from various locations in Uganda (Wakiso District), Tanzania (Tarangire National Park) and Kenya (Shimba Hills National Reserve, Muhaka, Nguruman) were collected. In Uganda, octenol baited F-traps were used to target tabanids, while NG2G traps baited with cow urine and acetone were employed in Kenya and Tanzania. The tabanids were identified using morphological and molecular methods. Morphologically, five genera (Ancala, Tabanus, Atylotus, Chrysops and Haematopota) and fourteen species of the Tabanidae were identified. Among the 14 species identified, six belonged to the genus Tabanus of which two (T.donaldsoni and T.guineensis) had not been described before in East Africa. The greatest diversity of tabanid species were collected from the Shimba Hills National Reserve, while collections from Uganda (around the shores of Lake Victoria) had the fewest number of species. However, the Ancala genus was found in Uganda, but not in Kenya or Tanzania. Maximum likelihood phylogenies of mitochondrial cytochrome c oxidase 1 (COI) genes sequenced in this study show definite concordance with morphological species identifications, except for Atylotus. This survey will be critical to building a complete checklist of Tabanidae prevalent in the region, expanding knowledge of these important vectors of human and animal diseases.

First described from western Kansas, USA, the western corn rootworm,Diabrotica virgifera virgifera, is one of the worst pests of maize. The species is generally thought to be of Mexican origin and to have incidentally followed the expansion of maize cultivation into North America thousands of years ago. However, this hypothesis has never been investigated formally. In this study, the genetic variability of samples collected throughout North America was analysed at 13 microsatellite marker loci to explore precisely the population genetic structure and colonization history ofD. v. virgifera. In particular, we used up-to-date Approximate Bayesian Computation methods based on random forest algorithms to test a Mexican versus a central-USA origin of the species, and to compare various possible timings of colonization. This analysis provided strong evidence that the origin ofD. v. virgiferawas southern (Mexico, or even further south). Surprisingly, we also found that the expansion of the species north of its origin was recent - probably not before 1100 years ago - thus indicating it was not directly associated with the early history of maize expansion out of Mexico, a far more ancient event.

Summary Variable, glutamine-encoding, CAA interruptions indicate that a property of the uninterrupted HTT CAG repeat sequence, distinct from the length of huntingtin’s polyglutamine segment, dictates the rate at which Huntington’s disease (HD) develops. The timing of onset shows no significant association with HTT cis-eQTLs but is influenced, sometimes in a sex-specific manner, by polymorphic variation at multiple DNA maintenance genes, suggesting that the special onset-determining property of the uninterrupted CAG repeat is a propensity for length instability that leads to its somatic expansion. Additional naturally occurring genetic modifier loci, defined by GWAS, may influence HD pathogenesis through other mechanisms. These findings have profound implications for the pathogenesis of HD and other repeat diseases and question the fundamental premise that polyglutamine length determines the rate of pathogenesis in the “polyglutamine disorders.”, Graphical Abstract, Highlights • Uninterrupted CAG repeat, not polyglutamine, size drives the timing of HD onset • HD age at onset is influenced by at least six genes involved in DNA maintenance • Genetic modifier loci often show both onset-delaying and onset-hastening haplotypes • The rate-determining mechanism is likely to be somatic expansion of the CAG repeat, The onset of Huntington’s disease is shown to be dependent on the size of the uninterrupted CAG repeat sequence, not polyglutamine.

In symbiotic cnidarians, acclimation to depth and lower irradiance can involve physio logical changes in the photosynthetic dinoflagellate endosymbiont, such as increased chlorophyll content, or qualitative modifications in the symbiont population in favour of better adapted strains. It has been argued that a lack of capacity to acquire new symbionts could limit the bathymetric distribution of the host species, or compromise its long-term survival in a changing environment. But is that always true? To address this question, we investigated the symbiont genetic diversity in Eunicella singularis, a Mediterranean sea whip species with a wide bathymet- ric distribution (10 to 50 m depth), which has recently suffered from mass mortalities after periods of abnormally high sea temperatures. We measured symbiont population densities and chloro- phyll content in natural populations, and followed the response of the holobionts after reciprocal transplantations to deep and shallow depths. A total of 161 colonies were sampled at 2 depths (10 and 30 m) at 5 sites in the northwestern Mediterranean. All colonies harboured a single ribosomal Symbiodinium clade (A'), but a relatively high within-clade genetic diversity was found among and within colonies. This diversity was not structured by depth, even though the deeper colonies contained significantly lower population densities of symbionts and less chlorophyll. We did, how- ever, reveal host-symbiont specificity among E. singularis and other Mediterranean cnidarian spe- cies. Transplantation experiments revealed a limit of plasticity for symbiont population density and chlorophyll content, which in turn questions the importance of the trophic role of Symbio- dinium in E. singularis.

Invasive species provide opportunities for investigating evolutionary aspects of colonization processes, including initial foundations of populations and geographic expansion. Using microsatellite markers and historical information, we characterized the genetic patterns of the invasion of the western corn rootworm (WCR), a pest of corn crops, in its largest area of expansion in Europe: Central and South-Eastern (CSE) Europe. We found that the invaded area probably corresponds to a single expanding population resulting from a single introduction of WCR and that gene flow is geographically limited within the population. In contrast to what is expected in classical colonization processes, an increase in genetic variation was observed from the center to the edge of the outbreak. Control measures against WCR at the center of the outbreak may have decreased effective population size in this area which could explain this observed pattern of genetic variation. We also found that small remote outbreaks in southern Germany and north-eastern Italy most likely originated from long-distance dispersal events from CSE Europe. We conclude that the large European outbreak is expanding by stratified dispersal, involving both continuous diffusion and discontinuous long-distance dispersal. This latter mode of dispersal may accelerate the expansion of WCR in Europe in the future.

Background Animal African Trypanosomiasis (AAT) is caused by several species of trypanosomes including Trypanosoma congolense, T. vivax, T. godfreyi, T. simiae and T. brucei. Two of the subspecies of T. brucei also cause Human African Trypanosomiasis. Although some of them can be mechanically transmitted by biting flies; these trypanosomes are all transmitted by tsetse flies which are the cyclical vectors of Trypanosoma congolense, T. godfreyi, T. simiae and T. brucei. We present here the first report assessing the prevalence of trypanosomes in tsetse flies in Nigeria using molecular tools. Methods 488 tsetse flies of three species, Glossina palpalis palpalis, G. tachinoides and G. morsitans submorsitans were collected from Wuya, Niger State and Yankari National Park, Bauchi State in 2012. Trypanosomes were detected and identified using an ITS1 PCR assay on DNA purified from the ‘head plus proboscis’ (H + P) and abdomen (ABD) parts of each fly. Results T. vivax and T. congolense Savannah were the major parasites detected. Trypanosomes prevalence was 7.1 % in G. p. palpalis, 11.9 % in G. tachinoides and 13.5 % in G. m. submorsitans. Prevalences of T. congolense Savannah ranged from 2.5 to 6.7 % and of T. vivax were approximately 4.5 %. Trypanosoma congolense Forest, T. godfreyi and T. simiae were also detected in the site of Yankari. The main biological and ecological determinants of trypanosome prevalence were the fly sex, with more trypanosomes found in females than males, and the site, with T. congolense subspp. being more abundant in Yankari than in Wuya. As expected, the trypanosome species diversity was higher in Yankari National Park than in the more agricultural site of Wuya where vertebrate host species diversity is lower. Conclusions Our results show that T. congolense Savannah and T. vivax are the main species of parasite potentially causing AAT in the two study sites and that Yankari National Park is a potential reservoir of trypanosomes both in terms of parasite abundance and species diversity. Electronic supplementary material The online version of this article (doi:10.1186/s13071-016-1585-3) contains supplementary material, which is available to authorized users.

It is known that in addition to repeat length variation, the exact sequence of the polyglutamine repeat tract and the adjacent polyproline also vary. Likewise, it is known that the expanded CAG is somatically unstable in a process that is age-dependent, tissue-specific and expansion biassed. Notably, very large alleles exceeding greater than 1,000 repeats are observed in a subset of striatal neurons. These data strongly suggest that somatic instability contributes toward the tissue specificity and progressive nature of the symptoms. Indeed, it has been shown that the frequency of large expansions in cortical cells correlates with variation in age at onset not accounted for by inherited repeat length. Most recently, it has been demonstrated that mismatch repair genes lie under some of the association peaks for genome wide analysis of variants contributing to variation in age at onset. Thus, in order to further address these issues, we have developed a high-throughput sequencing pipeline that allows us to determine the precise sequence of the polyglutamine and polyproline tracts. These studies have revealed an unexpectedly high frequency of atypical non-pathogenic alleles. We have also detected novel CCG interruptions within the CAG array in a large ‘premutation’ length allele. The majority of expanded HD alleles retain the expected structure of CAG and CCG repeats, but a subset of atypical pathogenic alleles have been detected. Using this approach we can also estimate the degree of somatic mosaicism present in the blood DNA of each participant. These data confirm that as expected, somatic mosaicism in the blood DNA of HD individuals is age- and allele length-dependent. We are currently attempting to understand how atypical alleles and individual-specific mutational dynamics contribute toward phenotypic variability in HD. We are also investigating how variants in the mismatch repair genes contribute toward variation in somatic mosaicism.

International audience; The western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae), is one of the most destructive pests of corn in North America and is currently invading Europe. The two major invasive outbreaks of rootworm in Europe have occurred, in North-West Italy and in Central and South-Eastern Europe. These two outbreaks originated from independent introductions from North America. Secondary contact probably occurred in North Italy between these two outbreaks, in 2008. We used 13 microsatellite markers to conduct a population genetics study, to demonstrate that this geographic contact resulted in a zone of admixture in the Italian region of Veneto. We show that i) genetic variation is greater in the contact zone than in the parental outbreaks; ii) several signs of admixture were detected in some Venetian samples, in a bayesian analysis of the population structure and in an approximate bayesian computation analysis of historical scenarios and, finally, iii) allelic frequency clines were observed at microsatellite loci. The contact between the invasive outbreaks in North-West Italy and Central and South-Eastern Europe resulted in a zone of admixture, with particular characteristics. The evolutionary implications of the existence of a zone of admixture in Northern Italy and their possible impact on the invasion success of the western corn rootworm are discussed.

Invasion biology and agriculture are intimately related for several reasons and in particular because many agricultural pest species are recent invaders. In this article we suggest that the reconstruction of invasion routes with population genetics-based methods can address fundamental questions in ecology and practical aspects of the management of biological invasions in agricultural settings. We provide a brief description of the methods used to reconstruct invasion routes and describe their main characteristics. In particular, we focus on a scenario--the bridgehead invasion scenario --which had been overlooked until recently. We show that this scenario, in which an invasive population is the source of other invasive populations, is evolutionarily parsimonious and may have played a crucial role in shaping the distribution of many recent agricultural pests., La biologie de l’invasion et l’agriculture sont intimement liées pour plusieurs raisons et en particulier parce que de nombreuses espèces de ravageurs agricoles sont des envahisseurs récents. Nous suggérons que la reconstruction des routes d’invasion par des méthodes de génétique des populations permet d’aborder des questions écologiques fondamentales et des aspects pratiques de la gestion des invasions biologiques en agriculture. Nous fournissons une brève description des méthodes utilisées pour reconstruire les routes d’invasion et décrivons leurs principales caractéristiques. En particulier, nous nous concentrons sur un scenario – le scenario d’invasion « tête de pont » – qui n’avait pas été considéré jusqu’à présent. Nous montrons que ce scenario, dans lequel une population envahissante est la source d’autres populations envahissantes, est parcimonieux du point de vue évolutif et a probablement joue un rôle crucial dans l’élaboration de la distribution géographique de nombreux ravageurs des cultures récents.

International audience; Determining the routes of introduction provides not only information about the history of an invasion process, but also information about the origin and construction of the genetic composition of the invading population. It remains difficult, however, to infer introduction routes from molecular data because of a lack of appropriate methods. We evaluate here the use of an approximate Bayesian computation (ABC) method for estimating the probabilities of introduction routes of invasive populations based on microsatellite data. We considered the crucial case of a single source population from which two invasive populations originated either serially from a single introduction event or from two independent introduction events. Using simulated datasets, we found that the method gave correct inferences and was robust to many erroneous beliefs. The method was also more efficient than traditional methods based on raw values of statistics such as assignment likelihood or pairwise F(ST). We illustrate some of the features of our ABC method, using real microsatellite datasets obtained for invasive populations of the western corn rootworm, Diabrotica virgifera virgifera. Most computations were performed with the DIYABC program (http://www1.montpellier.inra.fr/CBGP/diyabc/).

International audience; The early stages of invasion involve demographic bottlenecks that may result in lower genetic variation in introduced populations as compared to source population/s. Low genetic variability may decrease the adaptive potential of such populations in their new environments. Previous population genetic studies of invasive species have reported varying levels of losses of genetic variability in comparisons of source and invasive populations. However, intraspecific comparisons are required to assess more thoroughly the repeatability of genetic consequences of colonization events. Descriptions of invasive species for which multiple introductions from a single source population have been demonstrated may be particularly informative. The western corn rootworm (WCR), Diabrotica virgifera virgifera, native to North America and invasive in Europe, offers us an opportunity to analyse multiple introduction events within a single species. We investigated within- and between-population variation at eight microsatellite markers in WCR in North America and Europe to investigate the routes by which WCR was introduced into Europe, and to assess the effect of introduction events on genetic variation. We detected five independent introduction events from the northern USA into Europe. The diversity loss following these introductions differed considerably between events, suggesting substantial variation in introduction, foundation and/or establishment conditions. Genetic variability at evolutionarily neutral loci does not seem to underlie the invasive success of WCR in Europe. We also showed that the introduction of WCR into Europe resulted in the redistribution of genetic variance from the intra- to the interpopulational level contrary to most examples of multiple introductions.

International audience; The western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is a major pest of cultivated corn in North America and has recently begun to invade Europe. In addition to crop rotation, chemical control is an important option for D. v. virgifera management. However, resistance to chemical insecticides has evolved repeatedly in the USA. In Europe, chemical control strategies have yet to be harmonized and no surveys of insecticide resistance have been carried out. We investigated the resistance to methyl-parathion and aldrin of samples from nine D. v. virgifera field populations originating from two European outbreaks thought to have originated from two independent introductions from North America. Diagnostic concentration bioassays revealed that all nine D. v. virgifera field populations were resistant to aldrin but susceptible to methyl-parathion. Aldrin resistance was probably introduced independently, at least twice, from North America into Europe, as there is no evident selection pressure to account for an increase of frequency of aldrin resistance in each of the invasive outbreaks in Europe. Our results suggest that organophosphates, such as methyl-parathion, may still provide effective control of both larval and adult D. v. virgifera in the European invasive outbreaks studied.

Crop rotation has been a valuable technique for control of Diabrotica virgifera virgifera for almost a century. However, during the last two decades, crop rotation has ceased to be effective in an expanding area of the US corn belt. This failure appears to be due to a change in the insect's oviposition behaviour, which, in all probability, has an underlying genetic basis. A preliminary genome scan using 253 amplified fragment-length polymorphism (AFLP) markers sought to identify genetic variation associated with the circumvention of crop rotation. Samples of D. v. virgifera from east-central Illinois, where crop rotation is ineffective, were compared with samples from Iowa at locations that the behavioural variant has yet to reach. A single AFLP marker showed signs of having been influenced by selection for the circumvention of crop rotation. However, this marker was not diagnostic. The lack of markers strongly associated with the trait may be due to an insufficient density of marker coverage throughout the genome. A weak but significant general heterogeneity was observed between the Illinois and Iowa samples at microsatellite loci and AFLP markers. This has not been detected in previous population genetic studies of D. v. virgifera and may indicate a reduction in gene flow between variant and wild-type beetles.