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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. [...]

Background The transition from colonization to invasion is critical in diabetic foot ulcer (DFU). Staphylococcus aureus can colonize DFU, or invade the underlying tissues, causing serious infections. The ROSA-like prophage has previously been implicated in strain colonization characteristics of S aureus isolates in uninfected ulcers. Methods In this study, we investigated this prophage in the S aureus -colonizing strain using an in vitro chronic wound medium mimicking the chronic wound environment. Results Chronic wound medium reduced bacterial growth and increased biofilm formation and virulence in a zebrafish model. Conclusions The ROSA-like prophage promoted intracellular survival of S aureus -colonizing strain in macrophages, keratinocytes, and osteoblasts. [ABSTRACT FROM AUTHOR]

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.