Conserved requirement for DEAD-box RNA helicase Gemin3 in Drosophila oogenesis

Background: DEAD-box RNA helicase Gemin3 is an essential protein since its deficiency is lethal in both vertebrates and invertebrates. In addition to playing a role in transcriptional regulation and RNA silencing, as a core member of the SMN (survival of motor neurons) complex, Gemin3 is required for the biogenesis of spliceosomal snRNPs (small nuclear ribonucleoproteins), and axonal mRNA metabolism. Studies in the mouse and C. elegans revealed that loss of Gemin3 function has a negative impact on ovarian physiology and development. Findings. This work reports on the generation and characterisation of gemin3 mutant germline clones in Drosophila adult females. Gemin3 was found to be required for the completion of oogenesis and its loss led to egg polarity defects, oocyte mislocalisation, and abnormal chromosome morphology. Canonical Cajal bodies were absent in the majority of gemin3 mutant egg chambers and histone locus bodies displayed an atypical morphology. snRNP distribution was perturbed so that on gemin3 loss, snRNP cytoplasmic aggregates (U bodies) were only visible in wild type. Conclusions: These findings establish a conserved requirement for Gemin3 in Drosophila oogenesis. Furthermore, in view of the similarity to the phenotypes described previously in smn mutant germ cells, the present results confirm the close functional relationship between SMN and Gemin3 on a cellular level.peer-reviewe

A fruitful fly forward : the role of the fly in drug discovery for neurodegeneration

AD, Alzheimer’s disease; APP, amyloid precursor protein; BBB, blood brain barrier; GFP, green fluorescent protein; HTS, high-throughput screening; HD, Huntington’s disease; LB, Lewy bodies; PD, Parkinson’s disease; PolyQ, Polyglutamine; RNAi, RNA interference; SNCA, α-synuclein gene; UAS, Upstream Activating Sequence.peer-reviewe

Genetic animal models of Tourette syndrome : the long and winding road from lab to clinic

Tourette syndrome (TS) is a disabling neuropsychiatric disorder characterised by persistent motor and vocal tics. TS is a highly comorbid state, hence, patients might experience anxiety, obsessions, compulsions, sleep abnormalities, depression, emotional liability, learning problems, and attention deficits in addition to tics. In spite of its complex heterogeneous genetic aetiology, recent studies highlighted a strong link between TS and genetic lesions in the HDC (L-histidine decarboxylase) gene, which encodes the enzyme that synthetises histamine, and the SLITRK1 (SLIT and TRK-like family member 1) gene, which encodes a transmembrane protein that was found to regulate neurite outgrowth. In addition to validating the contribution of a specific genetic aberration to the development of a particular pathology, animal models are crucial to dissect the function of disease-linked proteins, expose disease pathways through examination of genetic modifiers and discover as well as assess therapeutic strategies. Mice with a knockout of either Hdc or Slitrk1 exhibit anxiety and those lacking Hdc, display dopamine agonist-triggered stereotypic movements. However, the mouse knockouts do not spontaneously display tics, which are recognised as the hallmark of TS. In this review, we explore the features of the present genetic animal models of TS and identify reasons for their poor resemblance to the human condition. Importantly, we highlight ways forward aimed at developing a valuable genetic model of TS or a model that has good predictive validity in developing therapeutic drugs for the treatment of tics, hence potentially accelerating the arduous journey from lab to clinic.peer-reviewe

Tourette syndrome : do reduced histamine levels induce an increase in spontaneous repetitive behaviour?

Gilles de la Tourette syndrome (TS) is a disabling neuropsychiatric disorder characterised by persistent motor and vocal tics. Comorbidity of TS with other neuropsychiatric conditions such as obsessive compulsive disorder (OCD), attention deficit hyperactivity disorder (ADHD) and autism is frequent. TS has a significant genetic contribution and, in this regard, several susceptibility loci have been identified including the histidine decarboxylase (HDC ) gene, which encodes an enzyme that is essential for histamine synthesis. Animal models of human disease are key to identify genetic and, importantly, pharmacological modifiers of phenotypes that mimic those present in the human condition. HDC is highly conserved throughout different species including the fruit fly Drosophila melanogaster. Aiming at uncovering TS-like phenotypes, in the present study we investigated repetitive grooming behaviour in flies that have reduced histamine levels as a result of a mutation in the hdc-encoding gene. We find that histamine deficiency in Drosophila is not associated with an increase in spontaneous repetitive grooming behaviour but rather a decrease. We speculate that the grooming behaviour in Drosophila hdc knockouts is not a translationally relevant TS phenotype. Future work should investigate whether stereotypy can be induced in the same mutants after pharmacological challenge or stress induction.peer-reviewe

GEMINs : potential therapeutic targets for spinal muscular atrophy?

The motor neuron degenerative disease spinal muscular atrophy (SMA) remains one of the most frequently inherited causes of infant mortality. Afflicted patients loose the survival motor neuron 1 (SMN1) gene but retain one or more copies of SMN2, a homolog that is incorrectly spliced. Primary treatment strategies for SMA aim at boosting SMN protein levels, which are insufficient in patients. SMN is known to partner with a set of diverse proteins collectively known as GEMINs to form a macromolecular complex. The SMN-GEMINs complex is indispensible for chaperoning the assembly of small nuclear ribonucleoproteins (snRNPs), which are key for pre-mRNA splicing. Pharmaceutics that alleviate the neuromuscular phenotype by restoring the fundamental function of SMN without augmenting its levels are also crucial in the development of an effective treatment. Their use as an adjunct therapy is predicted to enhance benefit to patients. Inspired by the surprising discovery revealing a premier role for GEMINs in snRNP biogenesis together with in vivo studies documenting their requirement for the correct function of the motor system, this review speculates on whether GEMINs constitute valid targets for SMA therapeutic development.peer-reviewe

SCFD1 in amyotrophic lateral sclerosis : reconciling a genetic association with in vivo functional analysis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive loss of upper and lower motor neurons, resulting in muscle weakness and spasticity, eventually leading to death due to respiratory failure. Analyses by our group of a case-control cohort from an isolated island population have found that genetics plays a significant role in disease etiology (Farrugia Wismayer et al., 2023). In addition to rare variants that cause familial monogenic forms of the disease, genetic variants that are commonly found in the population have also been associated with disease risk. To this end, the latest landmark cross-ancestry genome-wide association study (GWAS) identified multiple risk loci in patients with sporadic ALS or those without a family history of the disease (van Rheenen et al., 2021). Top-ranking loci identified in this study included the Sec1 Family Domain Containing 1 (SCFD1) gene and the uncoordinated 13 homolog A (UNC13A) gene based on association with the rs229195 and rs12608932 variants, respectively. Interestingly, although proteins encoded by SCFD1 and UNC13A have similar functions in vesicle transport and disruption of this pathway is well known to induce motor neuron degeneration (Mead et al., 2022), establishing a relationship between these risk genes and ALS pathophysiology has been challenging. This is nonetheless imperative because risk loci can be therapeutically targeted in a broad spectrum of ALS patients in addition to pre-symptomatic individuals with a higher ALS risk. Notably, recent studies have attempted to discover a potential link between major GWAS-identified risk loci and disease mechanism (Brown et al., 2022; Ma et al., 2022; Borg et al., 2023). For UNC13A, mis-splicing of its messenger RNA (mRNA) transcript in ALS patients was found to result in lower protein levels with serious consequences for synaptic maintenance (Brown et al., 2022; Ma et al., 2022). Making use of a pre-clinical model, we have shown that synaptic deficits and the resulting decline in neuromuscular function can also result from reduced levels of SCFD1 (Borg et al., 2023; Figure 1). Importantly, disease predisposition from loss of UNC13A or SCFD1 function may be intimately linked to protein misfolding and aggregation which remains a hallmark feature of ALS (Mead et al., 2022). Risk variants in the UNC13A locus are thought to be consequential in the absence of functional nuclear TDP-43 (Brown et al., 2022; Ma et al., 2022), a main constituent of cytoplasmic protein aggregates in ALS patients (Mead et al., 2022). A general downregulation of protein folding pathways may explain why the loss of SCFD1 leads to a decline in neuromuscular function (Borg et al., 2023).peer-reviewe

ACE and ACE2 : insights from Drosophila and implications for COVID-19

Angiotensin-converting enzyme (ACE) and its homologue ACE2 are key regulators of the renin-angiotensin system and thereby cardiovascular function through their zinc-metallopeptidase activity on vasoactive peptides. ACE2 also serves as the receptor for the cellular entry of various coronaviruses including the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is responsible for the coronavirus disease 2019 (COVID-19). The unprecedented scale of the COVID-19 pandemic has spurred the use of mammalian models to investigate the SARS-ACE2 relationship and knowledge gained from such research has accelerated development of vaccines and therapeutics. Recent studies have just started to underscore the utility of the fruit fly Drosophila melanogaster as a model system to study virus-host interactions and pathogenicity. Notably, the remarkable existence of catalytically functional ACE and ACE2 orthologues in Drosophila, discovered more than two decades ago, provides a unique opportunity for further developing this model organism to better understand COVID-19 in addition to identifying coronavirus preventative and therapeutic interventions targeting ACE2. Here, we review the studies that revealed crucial insights on the biochemistry and physiology of Ance and Acer, two out of the six Drosophila ACE family members with the greatest homology to human ACE and ACE2. We highlight shared in vivo functions outside of the renin-angiotensin system, which is not conserved in flies. Importantly, we identify knowledge gaps that can be filled by further research and outline ways that can raise Drosophila to a powerful model system to combat SARS-CoV-2 and its threatening vaccine-evading variants.peer-reviewe

Spinal Muscular Atrophy: From Defective Chaperoning of snRNP Assembly to Neuromuscular Dysfunction

Spinal Muscular Atrophy (SMA) is a neuromuscular disorder that results from decreased levels of the survival motor neuron (SMN) protein. SMN is part of a multiprotein complex that also includes Gemins 2–8 and Unrip. The SMN-Gemins complex cooperates with the protein arginine methyltransferase 5 (PRMT5) complex, whose constituents include WD45, PRMT5 and pICln. Both complexes function as molecular chaperones, interacting with and assisting in the assembly of an Sm protein core onto small nuclear RNAs (snRNAs) to generate small nuclear ribonucleoproteins (snRNPs), which are the operating components of the spliceosome. Molecular and structural studies have refined our knowledge of the key events taking place within the crowded environment of cells and the numerous precautions undertaken to ensure the faithful assembly of snRNPs. Nonetheless, it remains unclear whether a loss of chaperoning in snRNP assembly, considered as a “housekeeping” activity, is responsible for the selective neuromuscular phenotype in SMA. This review thus shines light on in vivo studies that point toward disturbances in snRNP assembly and the consequential transcriptome abnormalities as the primary drivers of the progressive neuromuscular degeneration underpinning the disease. Disruption of U1 snRNP or snRNP assembly factors other than SMN induces phenotypes that mirror aspects of SMN deficiency, and splicing defects, described in numerous SMA models, can lead to a DNA damage and stress response that compromises the survival of the motor system. Restoring the correct chaperoning of snRNP assembly is therefore predicted to enhance the benefit of SMA therapeutic modalities based on augmenting SMN expression

Reduced levels of ALS gene DCTN1 induce motor defects in Drosophila

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neuromuscular disease that has a strong genetic component. Deleterious variants in the DCTN1 gene are known to be a cause of ALS in diverse populations. DCTN1 encodes the p150 subunit of the molecular motor dynactin which is a key player in the bidirectional transport of cargos within cells. Whether DCTN1 mutations lead to the disease through either a gain or loss of function mechanism remains unresolved. Moreover, the contribution of non-neuronal cell types, especially muscle tissue, to ALS phenotypes in DCTN1 carriers is unknown. Here we show that gene silencing of Dctn1, the Drosophila main orthologue of DCTN1, either in neurons or muscles is sufficient to cause climbing and flight defects in adult flies. We also identify Dred, a protein with high homology to Drosophila Dctn1 and human DCTN1, that on loss of function also leads to motoric impairments. A global reduction of Dctn1 induced a significant reduction in the mobility of larvae and neuromuscular junction (NMJ) deficits prior to death at the pupal stage. RNA-seq and transcriptome profiling revealed splicing alterations in genes required for synapse organisation and function, which may explain the observed motor dysfunction and synaptic defects downstream of Dctn1 ablation. Our findings support the possibility that loss of DCTN1 function can lead to ALS and underscore an important requirement for DCTN1 in muscle in addition to neurons.peer-reviewe

SOD1 D91A variant in the southernmost tip of Europeb: a heterozygous ALS patient resident on the island of Gozo

Amyotrophic lateral sclerosis (ALS) is frequently caused by mutations in the SOD1 gene. Here, we report the first SOD1 variant in Malta, an archipelago of three inhabited islands in southern Europe. We describe a patient with a sporadic form of ALS living on the island of Gozo in which the heterozygous SOD1 c.272A>C; p.(Asp91Ala) variant was detected. The patient had a late onset (79 years), sensory impairments and rapid disease progression culminating in respiratory failure. ALS has not yet developed in any of the three additional family members in which the D91A variant was identified. None of the healthy controls from the Maltese population were found to carry this variant. This report underscores the high prevalence of the D91A variant in Europe, despite the presence of a North-South gradient in its frequency, and confirms that this variant can be associated with dominant cases in Mediterranean countries.peer-reviewe