Biology subjects

Giacomotto, J.

Publications and source records attributed to Giacomotto, J..

6 recordsLinked to original sources

bioRxiv2025

Modelling mental disorders in zebrafish. Neurexins severely modulate anxiety, social behaviours and aggression.

Can we reproduce mental disorders in zebrafish? To explore this question, we manipulated the neurexin gene family. Neurexin (nrxn) genes encode synaptic cell-adhesion molecules that have been repetitively associated with neurodevelopmental and mental disorders. While the zebrafish animal model offers tremendous advantages for dissecting neural development/function, no robust nrxn zebrafish models are currently available. In this study, we generated the first collection of zebrafish knockout lines for each nrxn gene, with mutations ranging from transmembrane domain- to full genomic locus-deletions. Surprisingly, all homozygous lines developed normally, presenting no gross neurodevelopmental or obvious early behavioural abnormalities. However, this absence of early phenotypes translated into profound, paralog-specific behavioural alterations emerging during juvenile-to-adult stages. All neurexin knockouts affected mating behaviour, complicating the generation and maintenance of homozygous lines. Except for this shared behavioural alteration, nrxn1, but not nrxn2 or nrxn3, led to marked changes in social behaviour and aggression. In contrast, nrxn2 mutants exhibited severe anxiety-like behaviours, including bottom-dwelling and repetitive freezing/seizure events. Strikingly, nrxn1 full-locus deletion mutants showed opposing behaviour, spending most of their time near the surface. The two also displayed opposite responses to open/closed field transitions; confinement alleviated nrxn2 anxiety but enhanced nrxn1 surface-dwelling. Meanwhile, nrxn3 mutants behaved normally in all our initial tests. In summary, our study introduces a complete set of zebrafish mutants covering the whole nrxn gene family, presenting striking juvenile/adult behavioural alterations despite the absence of noticeable early defects; echoing the delayed onset of human psychiatric disorders such as schizophrenia. This work demonstrates the value of zebrafish to study mental disorders and unlock a novel platform to unravel the pathogenic contribution of neurexin and associated subtle neurodevelopmental changes/timing that drive the emergence of mental illnesses.

neuroscience↗

bioRxiv2025

Clinical relevance of zebrafish for gene variants testing. Proof-of-principle with SMN1/SMA.

Spinal muscular atrophy (SMA) results from SMN1 gene loss-of-function (LOF), with disease severity directly linked to the level of remaining SMN protein. Nusinersen, risdiplam and onasemnogene abeparvovec are revolutionary treatments but should ideally be implemented before clinical symptoms appear. Because of this, prenatal and newborn screenings are increasingly used to identify common SMN1 mutations and patients requiring therapy. However, for novel mutations, clinicians lack robust analytic tools to predict pathogenicity before irreversible damage occurs. To address this gap, we deployed a zebrafish model presenting smn1-LOF, exhibiting progressive motor defects and death by only six days of age. We evaluated two SMN1-variants (VUS) identified in newborn patients awaiting definite diagnosis and treatment recommendations. We demonstrated that while known pathogenic variants did not change the disease course, wild-type SMN1 and both patient variants rescued SMA hallmarks in zebrafish, demonstrating the relevance of this approach for VUS-testing within a crucial timeframe for patients. Both VUS turned out to be non-pathogenic, and therapeutic costs of >US$2 million per child were avoided. Beyond SMA, this study provides robust proof-of-principle that the zebrafish represents a powerful translational tool for VUS-analysis, and that such approaches should be considered in clinical settings for supporting diagnosis and treatment decisions.

neuroscience↗

bioRxiv2024

Cre-Lox miRNA-delivery technology optimized for inducible microRNA and gene-silencing studies in zebrafish.

While many genetic tools exist for zebrafish, this animal model is still lacking a robust gene-silencing and microRNA-delivery technology enabling spatio-temporal control and reliable traceability. We have recently demonstrated that the use of engineered pri-miR backbones can be used to both trigger stable and heritable gene knockdown and/or express microRNA(s) of choice in this organism. This approach/material fills a gap that exists in the zebrafish genetic toolbox to study microRNA biology and has the potential to be a powerful complementary tool to CRISPR-knockout and CRISPR-interference approaches by enabling conditional, traceable tissue-specific and polygenic gene-silencing. However, to date, this miRNA-expressing technology still presents important limitations. First, to trigger potent knockdown(s), multiple synthetic-miRNAs must be expressed simultaneously which compromises the co-expression of fluorescent marker(s) and knockdown traceability, thereby reducing the interest and versatility of this approach. Second, when the gene knockdown triggers significant phenotypes, like homozygous mutants with severe early phenotypes, it is difficult, if not impossible, to maintain adult transgenic carriers. Here, to solve these problems and provide a mature RNAi and microRNA-delivery technology for zebrafish research, we have generated and validated new RNAi reagents and an inducible delivery system based on the Cre/Lox technology. This new system allows the creation of asymptomatic/silent carriers, easing the production of embryos with potent knockdowns that can be traced and spatiotemporally controlled. Following this technological development, we demonstrate the utility of our approach by generating novel inducible models of spinal muscular atrophy (SMA) that open new avenues for studying the normal and pathogenic functions of the smn1 gene, as well as for establishing large-scale screens. Finally, and very importantly, the materials and techniques developed here will simplify research into microRNA biology, as well as conditions involving haploinsufficiency and multiple genes.

molecular biology↗

bioRxiv2023

Flexing fish: cell surface plasticity in response to shape change in the whole organism

Plasma membrane rupture can result in catastrophic cell death. The skeletal muscle fibre plasma membrane, the sarcolemma, provides an extreme example of a membrane subject to mechanical stress since these cells specifically evolved to generate contraction and movement. A quantitative model correlating ultrastructural remodelling of surface architecture with tissue changes in vivo is required to understand how membrane domains contribute to the shape changes associated with tissue deformation in whole animals. We and others have shown that loss of caveolae, small invaginations of the plasma membrane particularly prevalent in the muscle sarcolemma, renders the plasma membrane more susceptible to rupture during stretch1-3. While it is thought that caveolae are able to flatten and be absorbed into the bulk membrane to buffer local membrane expansion, a direct demonstration of this model in vivo has been unachievable since it would require measurement of caveolae at the nanoscale combined with detailed whole animal morphometrics under conditions of perturbation. Here, we describe the development and application of the "active trapping model" where embryonic zebrafish are immobilised in a curved state that mimics natural body axis curvature during an escape response. The model is amenable to multiscale, multimodal imaging including high-resolution whole animal three-dimensional quantitative electron microscopy. Using the active trapping model, we demonstrate the essential role of caveolae in maintaining sarcolemmal integrity and quantify the specific contribution of caveolar-derived membrane to surface expansion. We show that caveolae directly contribute to an increase in plasma membrane surface area under physiologically relevant membrane deformation conditions.

cell biology↗

bioRxiv2021

Pipeline for generating stable large genomic deletions in zebrafish, from small domains to whole gene excisions

Here we describe a short feasibility study and methodological framework for the production of stable, CRISPR/Cas9-based, large genomic deletions in zebrafish, ranging from several base pairs (bp) to hundreds of kilobases (kb). Using a cocktail of four sgRNAs targeting a single genomic region mixed with a marker-sgRNA against the pigmentation gene tyrosinase (tyr), we demonstrate that one can easily and accurately excise genomic regions such as promoters, protein domains, specific exons or whole genes. We exemplify this technique with a complex gene family, neurexins, composed of three duplicated genes with multiple promoters and intricate splicing processes leading to thousands of isoforms. We precisely deleted small regions such as their transmembrane domains (150bp deletion in average) to their entire genomic locus (300kb deletion for nrxn1A for instance). We find that both the concentration and ratio of Cas9/sgRNAs are critical for the successful generation of these large deletions and, interestingly, that their transmission frequency does not decrease with increasing distance between sgRNA target sites. Considering the growing reports and debate about genetically compensated small indel mutants, the use of large-deletion approaches is likely to be widely adopted in studies of gene function. This strategy will also be key to the study of non-coding genomic regions.

genetics↗

bioRxiv2021

Muscle-specific Cavin4 interacts with Bin1 to promote T-tubule formation and stability in developing skeletal muscle

The cavin proteins are essential for caveola biogenesis and function. Here, we identify a role for the muscle-specific component, Cavin4, in skeletal muscle T-tubule development by analyzing two vertebrate systems: mouse and zebrafish. In both models Cavin4 localized to T-tubules and loss of Cavin4 resulted in aberrant T-tubule maturation. In zebrafish, which possess duplicated cavin4 paralogs, Cavin4b was shown to directly interact with the T-tubule-associated BAR domain protein, Bin1. Loss of both Cavin4a and Cavin4b caused aberrant accumulation of interconnected caveolae within the T-tubules, a fragmented T-tubule network enriched in Caveolin-3, and an impaired Ca2+ response upon mechanical stimulation. We propose a role for Cavin4 in remodeling the T-tubule membrane early in development by recycling caveolar components from the T-tubule to the sarcolemma. This generates a stable T-tubule domain lacking caveolae that is essential for T-tubule function.

cell biology↗