Search

Germline mutations that activate genes in the canonical RAS/MAPK signaling pathway are responsible for rare human developmental disorders known as RASopathies. Here, we analyzed the molecular determinants of Costello syndrome (CS) using a mouse model expressing HRAS p.G12S, patient skin fibroblasts, hiPSC-derived human cardiomyocytes, a HRAS p.G12V zebrafish model, and human fibroblasts expressing lentiviral constructs carrying HRAS p.G12S or HRAS p.G12A mutations. The findings revealed alteration of mitochondrial proteostasis and defective oxidative phosphorylation in the heart and skeletal muscle of CS mice that were also found in the cell models of the disease. The underpinning mechanisms involved the inhibition of the AMPK signaling pathway by mutant forms of HRAS, leading to alteration of mitochondrial proteostasis and bioenergetics. Pharmacological activation of mitochondrial bioenergetics and quality control restored organelle function in HRAS p.G12A and p.G12S cell models, reduced left ventricle hypertrophy in CS mice, and diminished the occurrence of developmental defects in the CS zebrafish model. Collectively, these findings highlight the importance of mitochondrial proteostasis and bioenergetics in the pathophysiology of RASopathies and suggest that patients with CS may benefit from treatment with mitochondrial modulators., Introduction Germline mutations that activate RAS/MAPK signaling are responsible for the 'RASopathies,' a group of rare human developmental diseases that affect more than 400,000 individuals in the United States alone. [...]

The ontogeny of haematopoietic stem cells (HSCs) during embryonic development is still highly debated, especially their possible lineage relationship to vascular endothelial cells (1,2). The first anatomical site from which cells with long-term HSC potential have been isolated is the aorta-gonad-mesonephros (AGM), more specifically the vicinity of the dorsal aortic floor (3). But although some authors have presented evidence that HSCs may arise directly from the aortic floor into the dorsal aortic lumen (4), others support the notion that HSCs first emerge within the underlying mesenchyme (5). Here we show by non-invasive, high-resolution imaging of live zebrafish embryos, that HSCs emerge directly from the aortic floor, through a stereotyped process that does not involve cell division but a strong bending then egress of single endothelial cells from the aortic ventral wall into the sub-aortic space, and their concomitant transformation into haematopoietic cells. The process is polarized not only in the dorso-ventral but also in the rostro-caudal versus medio-lateral direction, and depends on Runxl expression: in Runx1-deficient embryos, the exit events are initially similar, but much rarer, and abort into violent death of the exiting cell. These results demonstrate that the aortic floor is haemogenic and that HSCs emerge from it into the sub-aortic space, not by asymmetric cell division but through a new type of cell behaviour, which we call an endothelial haematopoietic transition., We (6,7) and others (8,9) have previously shown that in zebrafish embryos, the very thin space that initially separates the dorsal aorta (DA) from the underlying axial vein (AV) all [...]

In the mouse embryo, the onset of zygotic transcription occurs at the end of the first cell cycle, upon completion of DNA replication. We show that the nonhistone chromosomal protein HMG-I, whose translocation into the pronuclei of one-cell embryos is linked to this first round of DNA synthesis, plays a critical role in the activation of zygotic transcription. Indeed, microinjection of purified HMG-I results in a higher nuclear accumulation of the protein and triggers an earlier activation of zygotic transcription, an effect which is abolished by the preincubation of the protein with a specific antibody directed against its AT-hook DNA-binding motifs. Significantly, microinjection of this antibody also prevents the normal onset of transcription in the embryo, suggesting that endogenous HMG-I is similarly involved in this process. Finally, microinjection of the exogenous protein modifies chromatin structure as measured by in situ accessibility to DNase I. We propose that general chromosomal architectural factors such as HMG-I can modulate the accessibility of chromatin to specialized regulatory factors, thereby promoting a transcriptionally competent state. Key Words: colocalization software image analysis; early embryonic transcription; HMG-I; nuclear compartments; AT hook; scaffold-associated regions.

The article presents the study that identifies the macrophages vital in the diverse abilities of zebrafish using the polarization process in France.

The escalating prevalence of antibiotic-resistant bacterial infections necessitates urgent alternative therapeutic strategies. Phage therapy, which employs bacteriophages to specifically target pathogenic bacteria, emerges as a promising solution. This review examines the efficacy of phage therapy in zebrafish models, both embryos and adults, which are proven and reliable for simulating human infectious diseases. We synthesize findings from recent studies that utilized these models to assess phage treatments against various bacterial pathogens, including Enterococcus faecalis , Pseudomonas aeruginosa , Mycobacterium abscessus , Staphylococcus aureus , Klebsiella pneumoniae , Acinetobacter baumannii , and Escherichia coli . Methods of phage administration, such as circulation injection and bath immersion, are detailed alongside evaluations of survival rates and bacterial load reductions. Notably, combination therapies of phages with antibiotics show enhanced efficacy, as evidenced by improved survival rates and synergistic effects in reducing bacterial loads. We also discuss the transition from zebrafish embryos to adult models, emphasizing the increased complexity of immune responses. This review highlights the valuable contribution of the zebrafish model to advancing phage therapy research, particularly in the face of rising antibiotic resistance and the urgent need for alternative treatments., Competing Interests: The authors declare no conflict of interest.

Staphylococcus aureus is a pathogenic bacterium responsible for a broad spectrum of infections, including cutaneous, respiratory, osteoarticular, and systemic infections. It poses a significant clinical challenge due to its ability to develop antibiotic resistance. This resistance limits therapeutic options, increases the risk of severe complications, and underscores the urgent need for new strategies to address this threat, including the investigation of treatments complementary to antibiotics. The evaluation of novel antimicrobial agents often employs animal models, with the zebrafish embryo model being particularly interesting for studying host-pathogen interactions, establishing itself as a crucial tool in this field. For the first time, this study presents a zebrafish embryo model for the in vivo assessment of bacteriophage efficacy against S. aureus infection. A localized infection was induced by microinjecting either methicillin-resistant S. aureus (MRSA) or methicillin-susceptible S. aureus (MSSA). Subsequent treatments involved administering either bacteriophage, vancomycin (the reference antibiotic for MRSA), or a combination of both via the same route to explore potential synergistic effects. Our findings indicate that the bacteriophage was as effective as vancomycin in enhancing survival rates, whether used alone or in combination. Moreover, bacteriophage treatment appears to be even more effective in reducing the bacterial load in S. aureus -infected embryos post-treatment than the antibiotic. Our study validates the use of the zebrafish embryo model and highlights its potential as a valuable tool in assessing bacteriophage efficacy treatments in vivo ., Competing Interests: The authors declare no conflict of interest.

Cytosolic DNA promotes inflammatory responses upon detection by the cyclic GMP-AMP (cGAMP) synthase (cGAS). It has been suggested that cGAS downregulation is an immune escape strategy harnessed by tumor cells. Here, we used glioblastoma cells that show undetectable cGAS levels to address if alternative DNA detection pathways can promote pro-inflammatory signaling. We show that the DNA-PK DNA repair complex (i) drives cGAS-independent IRF3-mediated type I Interferon responses and (ii) that its catalytic activity is required for cGAS-dependent cGAMP production and optimal downstream signaling. We further show that the cooperation between DNA-PK and cGAS favors the expression of chemokines that promote macrophage recruitment in the tumor microenvironment in a glioblastoma model, a process that impairs early tumorigenesis but correlates with poor outcome in glioblastoma patients. Thus, our study supports that cGAS-dependent signaling is acquired during tumorigenesis and that cGAS and DNA-PK activities should be analyzed concertedly to predict the impact of strategies aiming to boost tumor immunogenicity., (© 2022 The Authors. Published under the terms of the CC BY 4.0 license.)

Mechanosensitivity is an inherent property of virtually all cell types, allowing them to sense and respond to physical environmental stimuli. Stretch-activated ion channels represent a class of mechanosensitive proteins which allow cells to respond rapidly to changes in membrane tension; however their identity has remained elusive. The piezo genes have recently been identified as a family of stretch-activated mechanosensitive ion channels. We set out to determine the role of piezo1 during zebrafish development. Here we report that morpholino-mediated knockdown of piezo1 impairs erythrocyte survival without affecting hematopoiesis or differentiation. Our results demonstrate that piezo1 is involved in erythrocyte volume homeostasis, disruption of which results in swelling/lysis of red blood cells and consequent anemia.