Abstract Cognitive impairments significantly impact the daily life of people with Down syndrome (DS). Overinhibition mediated by interneurons in the central nervous system was proposed as a key pathophysiological mechanism. Previous studies demonstrated cognitive rescue in the Ts65Dn mouse model using α5IA, a negative allosteric modulator of the α5 subunit-containing GABA A receptors. Here, we evaluated the effect of this drug in a mouse model carrying a more accurate duplication of the orthologous region to the human chromosome 21, namely the Dp(16)1Yey mouse model. First, we expanded the phenotypic characterization of Dp(16)1Yey mice using translationally more relevant behavioral tests. We confirmed spatial memory deficits in Dp(16)1Yey mice in the Barnes maze, and highlighted robust learning deficits in the pattern dissociation task and impairments in motor coordination. Next, we evaluated the effect of α5IA treatment on cognitive and motor performance. While α5IA treatment improved motor coordination in the Dp(16)1Yey mice, it failed to restore cognitive performance in the Barnes maze or in the pattern dissociation task. These findings could suggest divergent pathophysiological mechanisms between the Dp(16)1Yey and the Ts65Dn models. Potentially, it could explain the limited efficacy of similar pharmacological intervention in clinical trials for DS. Further preclinical studies should prioritize refined behavioral paradigms and probably the use of more complex DS models to enhance the translational potential of candidate therapies.

Cross-protection, discovered nearly a century ago, is a biological control method used to manage viral plant diseases. It is usually defined as a phenomenon in which a primary infection of a host by a pathogen (e.g., a mild strain) prevents its subsequent infection by a genetically related one (e.g., a severe related strain). Despite the long-standing research interest in this phenomenon from both a fundamental and an applied perspective, the mechanisms and factors-both viral and host-derived-underlying this phenomenon remain unclear, limiting its broader application. Proposed mechanisms include RNA silencing and potential roles of viral proteins, but inconsistent terminology and mixed evidence in the literature have made conclusions difficult. This review critically analyzes existing studies on plant virus cross-protection, summarizing common characteristics across systems and comparing them with proposed mechanisms. The findings suggest that cross-protection may result from different mechanisms that vary depending on the specific plant-virus interactions.

Beet mild yellowing virus (BMYV) and beet chlorosis virus (BChV) are two closely related poleroviruses infecting sugar beet plants, which induce leaf yellowing and cause high yield losses. Poleroviruses are phloem-limited and strictly transmitted by aphids in a circulative and persistent manner. In nature, sugar beet plants can be coinfected by these two viruses, but the outcome of BMYV and BChV coexistence in a plant on virus accumulation and aphid transmission has never been addressed before. In this study, we showed that the accumulation of each virus was not affected by the presence of the other, despite coinfecting about 40 % of infected phloem cells. Both viruses crossed the gut epithelium at the same site in Myzus persicae without any evidence of competition for receptor binding. On the contrary, when aphids simultaneously acquired both viruses from an artificial medium containing equal amounts of each virus, the transmission efficiency increased for both viruses. In contrast, only BMYV exhibited enhanced transmission when acquired from a coinfected plant. This suggests a cooperative effect at the inoculation step facilitating virus delivery in sugar beet cells by aphids. Our results shed light on fine-tuned virus-virus and virus-vector interactions, with potential implications for epidemiology and disease management.

Interneuron development is a crucial step of brain corticogenesis. When affected it often leads to brain dysfunctions like epilepsy, intellectual disabilities and autism spectrum disorder. Such defects are observed in the DYRK1A-haploinsufficiency syndrome, caused by mutations in DYRK1A, and commonly associated to cortical excitatory/inhibitory imbalance. However, how this imbalance is established in this syndrome remains elusive. Here, using mouse models and live imaging, we demonstrate that Dyrk1a specifically regulates the development of the cortical GABAergic system. We show that, unlike projection excitatory neurons, interneuron tangential migration relies on Dyrk1a dosage and kinase activity. We further reveal that Dyrk1a regulates actomyosin cytoskeleton remodeling during interneuron migration. Interestingly, mice with heterozygous inactivation of Dyrk1a in interneurons exhibited decreased interneuron density together with behavioral defects and epileptic activity, recapitulating phenotypes observed in human patients. Altogether, these data highlight the critical role of Dyrk1a in the development of the GABAergic system and the pathophysiology of DYRK1A-haploinsufficiency syndrome.

Most phytophagous insect species are specialized to feed on a narrow range of host plants, typically within the same genus or family, and sometimes even on a single plant species. However, some insect taxa are able to feed on plants from different families and are therefore considered to be generalists. Nevertheless, these generalist species can sometimes form cryptic species complexes or differentiate into host-based populations or races. Moreover, the host breadth of generalists is often measured under laboratory conditions, which may not accurately reflect the more challenging natural environments they encounter, and thus may lead to an overestimation of generalism. In this study, we used a population genetics approach to test whether Myzus persicae, a highly polyphagous aphid, is composed of host-specialized populations or clones, or whether generalism is an intrinsic characteristic of the species as a whole. We sampled M. persicae over four consecutive years in northern France from a variety of host plants belonging to different botanical families. We found that populations of M. persicae in northern France were predominantly composed of superclones, namely multilocus genotypes identified in many copies. In particular, four superclones dominated M. persicae populations, occurring in high proportions on a broad range of unrelated host plants in each year of the study. Moreover, the array of characterized genotypes of M. persicae formed distinct genetic clusters, but with no clear association to specific host plants. This study shows that under natural conditions and at the very fine genetic level of a single clone, the generalist characteristic of M. persicae holds. Thus, M. persicae remains an exceptional example of a true generalist species.

Cucurbit aphid-borne yellows virus (CABYV) presents a significant threat to cucurbit crops worldwide. Discovered in France in 1988, it rapidly spread to various regions, causing severe outbreaks primarily in warm Mediterranean areas and Asia. Classified in the family Solemoviridae, genus Polerovirus, CABYV exclusively inhabits plant phloem and is persistently transmitted by aphids. However, one exception in transmission was recently described for a CABYV isolate from Brazil transmitted by whiteflies. The virus has been detected across Europe, Asia, and Africa since its discovery. Recent studies indicate a concerning increase in the prevalence of CABYV in Northern Europe, along with the emergence of new isolates with higher virulence, new transmission vectors, and wider host ranges. The genetic structure of CABYV populations is influenced by purifying selection, resulting in distinct genetic groups in Asian and Mediterranean regions. Host factors and limited gene flow between geographically separated strains further contribute to genetic diversity. Recombination events result in the emergence of new variants, complicating disease management. While some resistance traits against CABYV have been identified in cucumber, squash, and melon, effective genetic resistance is still elusive. CABYV remains a significant worldwide threat to cucurbit crops. This review presents an update of CABYV biological features and will be published in the descriptions of plant viruses held by the Association of Applied Biologists as a new section dedicated to CABYV.

Turnip yellows virus (TuYV) is a plant virus infecting important crops such as oilseed rape. TuYV is phloem-restricted and transmitted by aphids. The capsid contains two subunit types: the major capsid protein (CP) and a minor component (RTP∗) which arises from the C-terminal cleavage of a readthrough product (RTP). RTP∗ contains the CP sequence fused with a structured domain, denoted NRTD, which is a key determinant of virus transmission. Though both CP and RTP∗ are involved in virus movement and aphid transmission, how RTP∗ is incorporated into the capsid is poorly understood. We present here the structural characterisation, by immunogold labelling and 3D cryo-EM, of the wild-type TuYV and a mutant whose capsid contains the CP only. We show that incorporation of RTP∗ does not impair the capsid structure, and the NRTD does not adopt well-defined positions at the capsid surface. The number of incorporated RTP∗s suggests a random insertion.

Plant viruses often alter host traits in ways that affect interactions with herbivores, potentially facilitating their own acquisition and transmission by insect vectors. However, little is known about the molecular mechanisms underlying this phenomenon. This is particularly true for agronomically important pathosystems, such as the viruses responsible for sugar beet yellowing. Among them is the beet chlorosis virus (BChV), whose effects on aphid vector behaviour and plant defence mechanisms have not been fully characterised. In this study, we demonstrate that BChV infection suppresses sugar beet defences induced by aphid pre-infestation, enhancing plant acceptability for aphids. Specifically, gene expression analyses revealed a downregulation of the aphid-induced ethylene pathway in infected plants, along with alterations in the salicylic acid pathway that may benefit aphids. Metabolic profiling highlighted reduced levels of phenolic acids, including cinnamic and coumaric acids, in virus-infected plants which likely contribute to increased plant acceptability by aphids. By integrating gene expression, metabolic profiling, and behavioural assays, our findings illustrate how BChV manipulates host-plant defences to potentially increase its transmission by aphids, underscoring the broad ecological and evolutionary significance of virus-mediated plant-vector interactions.

The green peach aphid (Myzus persicae) is a generalist pest damaging crops and transmitting viral pathogens. Using Illumina sequencing of small (s)RNAs and poly(A)-enriched long RNAs, we analyzed aphid virome components, viral gene expression and antiviral RNA interference (RNAi) responses. Myzus persicae densovirus (family Parvoviridae), a single-stranded (ss)DNA virus persisting in the aphid population, produced 22 nucleotide sRNAs from both strands of the entire genome, including 5 '- and 3 '-inverted terminal repeats. These sRNAs likely represent Dicer-dependent small interfering (si)RNAs, whose double-stranded RNA precursors are produced by readthrough transcription beyond poly(A) signals of the converging leftward and rightward transcription units, mapped here with Illumina reads. Additionally, the densovirus produced 26-28 nucleotide sRNAs, comprising those enriched in 5 '-terminal uridine and mostly derived from readthrough transcripts and those enriched in adenosine at position 10 from their 5 '-end and mostly derived from viral mRNAs. These sRNAs likely represent PIWI-interacting RNAs generated by a ping-pong mechanism. A novel ssRNA virus, reconstructed from sRNAs and classified into the family Flaviviridae, co-persisted with the densovirus and produced 22 nucleotide siRNAs from the entire genome. Aphids fed on plants versus artificial diets exhibited distinct RNAi responses affecting densovirus transcription and flavivirus subgenomic RNA production. In aphids vectoring turnip yellows virus (family Solemoviridae), a complete virus genome was reconstituted from 21, 22 and 24 nucleotide viral siRNAs likely acquired with plant phloem sap. Collectively, deep-sequencing analysis allowed for the identification and de novo reconstruction of M. persicae virome components and uncovered RNAi mechanisms regulating viral gene expression and replication.

As obligate intracellular parasites, viruses depend on host proteins and pathways for their multiplication. Among these host factors, specific nuclear proteins are involved in the life cycle of some cytoplasmic replicating RNA viruses, although their role in the viral cycle remains largely unknown. The polerovirus turnip yellows virus (TuYV) encodes a major coat protein (CP) and a 74 kDa protein known as the readthrough (RT) protein. The icosahedral viral capsid is composed of the CP and a minor component RT*, arising from a C-terminal cleavage of the full-length RT. In this study, we identified Arabidopsis (Arabidopsis thaliana) ALY family proteins as interacting partners of TuYV structural proteins using yeast 2-hybrid assays and co-immunoprecipitations in planta. ALY proteins are adaptor proteins of the THO-TREX-1 complex essential to the nuclear export of mature messenger RNAs (mRNAs). Although all 4 ALY proteins colocalized with the CP and the RT protein in the nucleus upon co-expression in agro-infiltrated Nicotiana benthamiana leaves, only the CP remained nuclear and colocalized with ALY proteins in TuYV-infected cells, suggesting that the CP is an essential partner of ALY proteins. Importantly, TuYV-infected A. thaliana 4xaly knock-out mutants showed a significant increase in viral accumulation, indicating that TuYV infection is affected by an unknown ALY-mediated antiviral defense mechanism or impairs the cellular mRNA export pathway to favor viral RNA translation. This finding underpins the crucial role played by nuclear factors in the life cycle of cytoplasmic RNA viruses. The interaction identified between RNA-binding ALY proteins and turnip yellows virus structural proteins possibly contributes to antiviral defense or reduced cellular messenger RNA export.

The polerovirus turnip yellows virus (TuYV) (formerly beet western yellows virus, BWYV) is a member of the genus Polerovirus in the family Solemoviridae . It is transmitted from plant to plant by aphids according to a circulative and non-propagative mode. TuYV has a wide host range among herbaceous plants and infects important crops such as oilseed rape. Members of the Solemoviridae family are strictly restricted to the three cell types constituting the phloem; the nucleated phloem parenchyma cells and companion cells, where the virus replicates, and the sieve elements, which convey the virus to sites distant from the inoculation point. TuYV consists of a single-stranded positive sense RNA genome of approximately 6 kb encapsidated into an icosahedral capsid of approximately 30 nm in diameter. The capsid is composed of two types of subunits: the major capsid protein (CP, ~23 kDa) and a minor component, denoted RTP* (~54 kDa), which arises from the C-terminal cleavage of a readthrough gene product (RTP, 74 kDa). The minor capsid component contains the CP sequence at its N-terminus fused with a structured domain (denoted NRTD) which has been shown to be a key determinant of virus transmission and necessary for crossing aphid gut epithelial cells during viral uptake. Though both the CP and RTP* structural proteins are involved in virus movement and aphid transmission, how RTP* is incorporated in the viral particles is poorly understood. We present here the structural characterisation of the TuYV wild-type virions (viral capsids containing both CP and RPT*) and a mutant whose capsids contain the CP only. The comparison of the cryo-EM maps of the wild-type and the mutated virus (resolved at 4.1 and 3.5 Å respectively) reveals that the RTP* does not impair the structural organization of the capsid shell. Furthermore, electron cryo-microscopy and immunogold labelling observations of both viruses indicate that the NRTDs do not adopt well-defined positions relative to the capsid surface, and that only four to six NRTDs or NRTD dimers are incorporated into the viral particles, suggesting a random insertion of the RTP* into the TuYV capsid. ### Competing Interest Statement The authors have declared no competing interest.

Many plant viruses modify the phenotype of their hosts, which may influence the behaviour of their vectors and facilitate transmission. Among them is the turnip yellows virus (TuYV), which can modify the orientation, feeding, and performance of its main aphid vector, Myzus persicae. However, the virus factors driving these mechanisms have not been elucidated. In this study, we compared the feeding behaviour and fecundity of aphids on TuYV-infected and transgenic Arabidopsis thaliana expressing individual TuYV proteins (CP, RT and P0) to define the role of these proteins in aphid-plant interactions. Aphids on TuYV-infected plants had shorter pathway phases and ingested phloem sap for longer times, which is expected to promote the acquisition of the phloem-limited TuYV. No change in aphid fecundity was observed on TuYV-infected plants. The transmission-conducive feeding behaviour changes could be fully reproduced by phloem-specific expression of the capsid protein (CP) in transgenic plants, whereas expression of P0 had minor and RT had no effects on aphid feeding behaviour. We then carried out a metabolomic analysis to determine plant compounds that could be involved in the modification of the aphid behaviour. A few metabolites were specific for TuYV-infected or CP-transgenic A. thaliana, and are good candidates for inducing behavioural changes.

Multi-infection of plants by viruses is very common and can change drastically infection parameters such as virus accumulation, distribution, and vector transmission. Sugar beet is an important crop that is frequently co-infected by the polerovirus beet chlorosis virus (BChV) and the closterovirus beet yellows virus (BYV), both vectored by the green peach aphid (Myzus persicae). These phloem-limited viruses are acquired while aphids ingest phloem sap from infected plants. Here we found that co-infection decreased transmission of BChV by ~50% but had no impact on BYV transmission. The drastic reduction of BChV transmission was due to neither lower accumulation of BChV in co-infected plants nor reduced phloem sap ingestion by aphids from these plants. Using the signal amplification by exchange reaction fluorescent in situ hybridization technique on plants, we observed that 40% of the infected phloem cells were co-infected and that co-infection caused redistribution of BYV in these cells. The BYV accumulation pattern changed from distinct intracellular spherical inclusions in mono-infected cells to a diffuse form in co-infected cells. There, BYV co-localized with BChV throughout the cytoplasm, indicative of virus-virus interactions. We propose that BYV-BChV interactions could restrict BChV access to the sieve tubes and reduce its accessibility for aphids and present a model of how co-infection could alter BChV intracellular movement and/or phloem loading and reduce BChV transmission.IMPORTANCEMixed viral infections in plants are understudied yet can have significant influences on disease dynamics and virus transmission. We investigated how co-infection with two unrelated viruses, BChV and BYV, affects aphid transmission of the viruses in sugar beet plants. We show that co-infection reduced BChV transmission by about 50% without affecting BYV transmission, despite similar virus accumulation rates in co-infected and mono-infected plants. Follow-up experiments examined the localization and intracellular distribution of the viruses, leading to the discovery that co-infection caused a redistribution of BYV in the phloem vessels and altered its repartition pattern within plant cells, suggesting virus-virus interactions. In conclusion, the interplay between BChV and BYV affects the transmission of BChV but not BYV, possibly through direct or indirect virus-virus interactions at the cellular level. Understanding these interactions could be crucial for managing virus propagation in crops and preventing yield losses.

Down syndrome (DS) is caused by trisomy of human chromosome 21 (Hsa21). DS is a gene dosage disorder that results in multiple phenotypes including congenital heart defects. This clinically important cardiac pathology is the result of a third copy of one or more of the approximately 230 genes on Hsa21, but the identity of the causative dosage–sensitive genes and hence mechanisms underlying this cardiac pathology remain unclear. Here, we show that hearts from human fetuses with DS and embryonic hearts from the Dp1Tyb mouse model of DS show reduced expression of mitochondrial respiration genes and cell proliferation genes. Using systematic genetic mapping, we determined that three copies of the dual-specificity tyrosine phosphorylation–regulated kinase 1A ( Dyrk1a ) gene, encoding a serine/threonine protein kinase, are associated with congenital heart disease pathology. In embryos from Dp1Tyb mice, reducing Dyrk1a gene copy number from three to two reversed defects in cellular proliferation and mitochondrial respiration in cardiomyocytes and rescued heart septation defects. Increased dosage of DYRK1A protein resulted in impairment of mitochondrial function and congenital heart disease pathology in mice with DS, suggesting that DYRK1A may be a useful therapeutic target for treating this common human condition.

BackgroundAutism spectrum disorders affect more than 1% of the population, impairing social communication and increasing stereotyped behaviours. A micro-deletion of the 16p11.2 BP4-BP5 chromosomic region has been identified in 1% of patients also displaying intellectual disabilities. In mouse models generated to understand the mechanisms of this deletion, learning and memory deficits were pervasive in most genetic backgrounds, while social communication deficits were only detected in some models.MethodsTo complement previous studies, we itemized the social deficits in the mouse model of 16p11.2 deletion on a hybrid C57BL/6N × C3H.Pde6b+ genetic background. We examined whether behavioural deficits were visible over long-term observation periods lasting several days and nights, to parallel everyday-life assessment of patients. We recorded the individual and social behaviours of mice carrying a heterozygous deletion of the homologous 16p11.2 chromosomic region (hereafter Del/+) and their wild-type littermates from both sexes over two or three consecutive nights during social interactions of familiar mixed-genotype quartets of males and of females, and of same-genotype unfamiliar female pairs.ResultsWe observed that Del/+ mice of both sexes increased significantly their locomotor activity compared to wild-type littermates. In the social domain, Del/+ mice of both sexes displayed widespread deficits, even more so in males than in females in quartets of familiar individuals. In pairs, significant perturbations of the organisation of the social communication and behaviours appeared in Del/+ females.DiscussionAltogether, this suggests that, over long recording periods, the phenotype of the 16p11.2 Del/+ mice was differently affected in the locomotor activity and the social domains and between the two sexes. These findings confirm the importance of testing models in long-term conditions to provide a comprehensive view of their phenotype that will refine the study of cellular and molecular mechanisms and complement pre-clinical targeted therapeutic trials.

The success of virus transmission by vectors relies on intricate trophic interactions between three partners, the host plant, the virus, and the vector. Despite numerous studies that showed the capacity of plant viruses to manipulate their host plant to their benefit, and potentially of their transmission, the molecular mechanisms sustaining this phenomenon has not yet been extensively analyzed at the molecular level. In this study, we focused on the deregulations induced in Arabidopsis thaliana by an aphid vector that were alleviated when the plants were infected with turnip yellows virus (TuYV), a polerovirus strictly transmitted by aphids in a circulative and nonpropagative mode. By setting up an experimental design mimicking the natural conditions of virus transmission, we analyzed the deregulations in plants infected with TuYV and infested with aphids by a dual transcriptomic and metabolomic approach. We observed that the virus infection alleviated most of the gene deregulations induced by the aphids in a noninfected plant at both time points analyzed (6 and 72 h) with a more pronounced effect at the later time point of infestation. The metabolic composition of the infected and infested plants was altered in a way that could be beneficial for the vector and the virus transmission. Importantly, these substantial modifications observed in infected and infested plants correlated with a higher TuYV transmission efficiency. This study revealed the capacity of TuYV to alter the plant nutritive content and the defense reaction against the aphid vector to promote the viral transmission.

Stefin B (cystatin B) is an inhibitor of lysosomal and nuclear cysteine cathepsins. The gene for stefin B is located on human chromosome 21 and its expression is upregulated in the brains of individuals with Down syndrome. Biallelic loss-of-function mutations in the stefin B gene lead to Unverricht–Lundborg disease-progressive myoclonus epilepsy type 1 (EPM1) in humans. In our past study, we demonstrated that mice lacking stefin B were significantly more sensitive to sepsis induced by lipopolysaccharide (LPS) and secreted higher levels of interleukin 1-β (IL-1β) due to increased inflammasome activation in bone marrow-derived macrophages. Here, we report lower interleukin 1-β processing and caspase-11 expression in bone marrow-derived macrophages prepared from mice that have an additional copy of the stefin B gene. Increased expression of stefin B downregulated mitochondrial reactive oxygen species (ROS) generation and lowered the NLR family pyrin domain containing 3 (NLRP3) inflammasome activation in macrophages. We determined higher AMP-activated kinase phosphorylation and downregulation of mTOR activity in stefin B trisomic macrophages—macrophages with increased stefin B expression. Our study showed that increased stefin B expression downregulated mitochondrial ROS generation and increased autophagy. The present work contributes to a better understanding of the role of stefin B in regulation of autophagy and inflammasome activation in macrophages and could help to develop new treatments.

ABSTRACT Interneuron development is a crucial step of brain corticogenesis. When affected it often leads to brain dysfunctions, such as epilepsy, intellectual disabilities and autism spectrum disorder. Such defects are observed in the DYRK1A -haploinsufficiency syndrome, caused by mutations of DYRK1A , and commonly associated to cortical excitatory/inhibitory imbalance. However, how this imbalance is established in this syndrome remains elusive. Here, using mouse models and live imaging, we show that Dyrk1a specifically regulates the development of the cortical GABAergic system. Unlike projection excitatory neurons, we demonstrate that interneuron tangential migration relies on Dyrk1a dosage and kinase activity through a mechanism involving actomyosin cytoskeleton remodeling. Interestingly, we further demonstrate that mice with heterozygous inactivation of Dyrk1a in interneurons show behavioral defects and epileptic activity, recapitulating phenotypes observed in human patients. Altogether, these data highlight the critical role of Dyrk1a in the development of the GABAergic system and the pathophysiology of DYRK1A -haploinsufficiency syndrome.