Systematic identification of factors involved in the silencing of germline genes in mouse embryonic stem cells

In mammals, many germline genes are epigenetically repressed to prevent their illegitimate expression in somatic cells. To advance our understanding of the mechanisms restricting the expression of germline genes, we analyzed their chromatin signature and performed a CRISPR-Cas9 knock-out screen for genes involved in germline gene repression using a Dazl-GFP reporter system in mouse embryonic stem cells (mESCs). We show that the repression of germline genes mainly depends on the polycomb complex PRC1.6 and DNA methylation, which function additively in mESCs. Furthermore, we validated novel genes involved in the repression of germline genes and characterized three of them: Usp7, Shfm1 (also known as Sem1) and Erh. Inactivation of Usp7, Shfm1 or Erh led to the upregulation of germline genes, as well as retrotransposons for Shfm1, in mESCs. Mechanistically, USP7 interacts with PRC1.6 components, promotes PRC1.6 stability and presence at germline genes, and facilitates DNA methylation deposition at germline gene promoters for long term repression. Our study provides a global view of the mechanisms and novel factors required for silencing germline genes in embryonic stem cells

Liver fibrosis staging using supersonic shear imaging : a clinical study on 142 patients

International audienceI. Background, Motivation and ObjectiveFibrosis staging can be assessed by a rough estimation of the liver stiffness averaged along an ultrasonic A-line. Providing a complete 2D map of liver stiffness would thus be of great clinical interest for the diagnosis of hepatic fibrosis and help prevent upcoming cirrhosis. However, such measurement requires both a quantitative value of shear elasticity and a great precision to discriminate between different fibrosis levels. Beyond the scope of non-invasive fibrosis quantification, it is also envisioned that quantitative elasticity imaging of liver will have potential interest for liver cancer diagnosis. In this work, the Supersonic Shear Imaging technique (SSI) is proposed to map the in vivo viscoelastic parameters of liver on patients with hepatitis C and derive a mean elasticity of liver tissues. The results are compared to biological tests (Fib4, Apri, Forns) and Fibroscan® measurements. II. Statement of Contribution / MethodsThe SSI technique is based on the radiation force induced by a conventional ultrasonic probe to generate a planar shear wave deep into tissues. The shear wave propagation throughout the medium is caught in real time thanks to an ultrafast ultrasound scanner (up to 5000 frames/s). Using modified sequences and post-processing, this technique is implemented on curved arrays in order to get a larger field of view of liver tissues. A study on 150 HCV patients with different fibrosis stages F has been conducted in order to investigate the accuracy of the technique (F ϵ [0;4]). Quantitative maps of liver elasticity are produced for each volunteer with a linear and a curved array. III. ResultsB-mode images of 120x75 mm² and corresponding elasticity maps are obtained using a 2.5 MHz curved ultrasonic probe with a good reproducibility and accuracy. The shear wave phase velocity dispersion is also calculated. This study shows a good correlation between the values obtained by SSI and the fibrosis levels diagnosed by biological tests (p-index 0.9 for F>3 and Y> 0.8 for F>2). Results are also compared (r2 > 0.92) to the Fibroscan® elasticity measurement by fitting the velocity dispersion curves obtained by SSI at 50 Hz.IV. Discussion and ConclusionsThis real-time elasticity mapping using an ultrasonic curved probe offers better signal to noise ratio than linear arrays and a larger area in the patient's liver (13.3±2.8 cm² estimation area). This gives more confidence on the accuracy of the diagnosis of the fibrosis stage. Furthermore, the elasticity parameters obtained with SSI give access to the shear wave group velocity and the phase velocity. As a consequence, the SSI assessment of liver stiffness could potentially give more information on the viscoelasticity properties of the liver

E2F6 initiates stable epigenetic silencing of germline genes during embryonic development.

In mouse development, long-term silencing by CpG island DNA methylation is specifically targeted to germline genes; however, the molecular mechanisms of this specificity remain unclear. Here, we demonstrate that the transcription factor E2F6, a member of the polycomb repressive complex 1.6 (PRC1.6), is critical to target and initiate epigenetic silencing at germline genes in early embryogenesis. Genome-wide, E2F6 binds preferentially to CpG islands in embryonic cells. E2F6 cooperates with MGA to silence a subgroup of germline genes in mouse embryonic stem cells and in embryos, a function that critically depends on the E2F6 marked box domain. Inactivation of E2f6 leads to a failure to deposit CpG island DNA methylation at these genes during implantation. Furthermore, E2F6 is required to initiate epigenetic silencing in early embryonic cells but becomes dispensable for the maintenance in differentiated cells. Our findings elucidate the mechanisms of epigenetic targeting of germline genes and provide a paradigm for how transient repression signals by DNA-binding factors in early embryonic cells are translated into long-term epigenetic silencing during mouse development

Autoethnography and practical philosophy

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faire du terrain en philosophie : un problème de légitimité

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Pour une critique féministe de l'éducation thérapeutique en contexte d'endométriose

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Genre et handicap : quels enjeux ?

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