In vivo testing of microRNA-mediated gene knockdown in zebrafish

MiR-107 inhibits the sprouting of intersegmental vessels of zebrafish embryos

MicroRNAs (miRNAs) play important roles in various biological processes. Our previous study showed that inhibition of MTOR with rapamycin treatment suppressed human endothelial cell tube formation, concomitant with the down-regulation of miR-107. Similarly, inhibition of Ztor by rapamycin also suppressed vascular development in zebrafish embryos. To gain a better understanding of the role of miR-107 and MTOR in vascular development, the present study sought to validate its function by over-expressing miR-107 in zebrafish embryos via microinjection with mimic miR-107 duplexes. Alkaline phosphatase (ALP) staining was used to visualise blood vessels in the zebrafish embryo, and expressions of Pten, Ztor and Rap1 were investigated by immunoblotting. Over-expression of miR-107 in zebrafish embryos inhibited the sprouting of intersegmental vessels (ISVs) with concomitant down-regulation of phosphorylated Rps6 expression, which confirmed the inhibition of Ztor signalling. As expected, pten, which is the target of miR-107, was down-regulated. Interestingly, Rap1, a small GTPase protein that is involved in intersomitic vessels sprouting during angiogenesis, was also down-regulated when miR-107 was over-expressed. Overall, our findings suggest that miR-107 and Ztor-mediated suppression of vascular development in zebrafish embryo involves Rap1.

Reduced C9orf72 function leads to defective synaptic vesicle release and neuromuscular dysfunction in zebrafish

The most common genetic cause of amyotrophic lateral sclerosis (ALS) and fronto-temporal dementia (FTD) is a hexanucleotide repeat expansion within the C9orf72 gene. Reduced levels of C9orf72 mRNA and protein have been found in ALS/FTD patients, but the role of this protein in disease pathogenesis is still poorly understood. Here, we report the generation and characterization of a stable C9orf72 loss-of-function (LOF) model in the zebrafish. We show that reduced C9orf72 function leads to motor defects, muscle atrophy, motor neuron loss and mortality in early larval and adult stages. Analysis of the structure and function of the neuromuscular junctions (NMJs) of the larvae, reveal a marked reduction in the number of presynaptic and postsynaptic structures and an impaired release of quantal synaptic vesicles at the NMJ. Strikingly, we demonstrate a downregulation of SV2a upon C9orf72-LOF and a reduced rate of synaptic vesicle cycling. Furthermore, we show a reduced number and size of Rab3a-postive synaptic puncta at NMJs. Altogether, these results reveal a key function for C9orf72 in the control of presynaptic vesicle trafficking and release at the zebrafish larval NMJ. Our study demonstrates an important role for C9orf72 in ALS/FTD pathogenesis, where it regulates synaptic vesicle release and neuromuscular functions.

Butti et al. generate a C9orf72 loss-of-function model in zebrafish. They find that that C9orf72 is required for presynaptic vesicle trafficking and release at the zebrafish larval neuromuscular junctions. This study provides functional insights into the pathogenesis of amyotrophic lateral sclerosis and fronto-temporal dementia.

Modelling C9orf72-Related Amyotrophic Lateral Sclerosis in Zebrafish

A hexanucleotide repeat expansion within the C9orf72 gene is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and its discovery has revolutionized our understanding of this devastating disease. Model systems are a valuable tool for studying ALS pathobiology and potential therapies. The zebrafish (Danio rerio) has particularly become a useful model organism to study neurological diseases, including ALS, due to high genetic and physiological homology to mammals, and sensitivity to various genetic and pharmacological manipulations. In this review we summarize the zebrafish models that have been used to study the pathology of C9orf72-related ALS. We discuss their value in providing mechanistic insights and their potential use for drug discovery.

High throughput sequencing of small RNAs transcriptomes in two Crassostrea oysters identifies microRNAs involved in osmotic stress response

Increasing evidence suggests that microRNAs post-transcriptionally regulate gene expression and are involved in responses to biotic and abiotic stress. However, the role of miRNAs involved in osmotic plasticity remains largely unknown in marine bivalves. In the present study, we performed low salinity challenge with two Crassostrea species (C. gigas and C. hongkongensis), and conducted high-throughput sequencing of four small RNA libraries constructed from the gill tissues. A total of 202 and 87 miRNAs were identified from C. gigas and C. hongkongensis, respectively. Six miRNAs in C. gigas and two in C. hongkongensis were differentially expressed in response to osmotic stress. The expression profiles of these eight miRNAs were validated by qRT-PCR. Based on GO enrichment and KEGG pathway analysis, genes associated with microtubule-based process and cellular component movement were enriched in both species. In addition, five miRNA-mRNA interaction pairs that showed opposite expression patterns were identified in the C. hongkongensis, Differential expression analysis identified the miRNAs that play important regulatory roles in response to low salinity stress, providing insights into molecular mechanisms that are essential for salinity tolerance in marine bivalves.

Effective heritable gene knockdown in zebrafish using synthetic microRNAs

Although zebrafish is used to model human diseases through mutational and morpholino-based knockdown approaches, there are currently no robust transgenic knockdown tools. Here we investigate the knockdown efficiency of three synthetic miRNA-expressing backbones and show that these constructs can downregulate a sensor transgene with different degrees of potency. Using this approach, we reproduce spinal muscular atrophy (SMA) in zebrafish by targeting the smn1 gene. We also generate different transgenic lines, with severity and age of onset correlated to the level of smn1 inhibition, recapitulating for the first time the different forms of SMA in zebrafish. These lines are proof-of-concept that miRNA-based approaches can be used to generate potent heritable gene knockdown in zebrafish.

Zebrafish is a model system for which for no reliable heritable gene silencing method is available. Here the authors provide a system for heritable miRNA-mediated knockdown and demonstrate tunable silencing of the smn1 gene that recapitulate different forms of spinal muscular atrophy.