Placenta

Résumé

thumb|250px|right|Le placenta et le cordon ombilical. On remarque la forte vascularisation de la membrane. Le placenta est un organe unique qui connecte physiquement et biologiquement l'embryon en développement à la paroi utérine. Durant toute la grossesse, le placenta apporte à l'embryon puis au fœtus l'eau, les nutriments et le dioxygène dont il a besoin. Il évacue aussi le dioxyde de carbone et les déchets métaboliques tels que l'urée, excrétés par l'embryon. Il produit et secrète des hormones qui maintiennent la grossesse et « manipulent » la physiologie maternelle au profit du fœtus. Dans la classification du vivant traditionnelle, le placenta définit les fameux mammifères placentaires, dont l'être humain fait partie. En réalité, il s'agit d'un organe commun aux thériens, bien que plus rudimentaire chez les métathériens (dont les marsupiaux), ces derniers naissant au stade larvaire et poursuivant la majeure partie de leur développement hors de l'utérus maternel ; tandis que les

Source officielle

https://fr.wikipedia.org/wiki/Placenta

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Ce cours présente les principes fondamentaux à l'œuvre dans les organismes vivants. Autant que possible, l'accent est mis sur les contributions de l'Informatique aux progrès des Sciences de la Vie.

Ce cours décrit le fonctionnement du système immunitaire humain et les bases immunologiques de la vaccination, de la transplantation, de l'immunothérapie, et de l'allergie. Il présente aussi le rôle des cellules souches dans la formation des tissus, notamment la lignée hématopoïétique.

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The serine protease CAP1/Prss8 is crucial for skin barrier function, lung alveolar fluid clearance and has been unveiled as diagnostic marker for specific cancer types. Here, we show that a constitutive knockout of CAP1/Prss8 leads to embryonic lethality. These embryos presented no specific defects, but it is during this period, and in particular at E13.5, that wildtype placentas show an increased expression of CAP1/Prss8, thus suggesting a placental defect in the knockout situation. The placentas of knockout embryos exhibited significantly reduced vascular development and incomplete cellular maturation. In contrary, epiblast-specific deletion of CAP1/Prss8 allowed development until birth. These CAP1/Prss8-deficient newborns presented abnormal epidermis, and died soon after birth due to impaired skin function. We thus conclude that a late placental insufficiency might be the primary cause of embryonic lethality in CAP1/Prss8 knockouts. This study highlights a novel and crucial role for CAP1/Prss8 in placental development and function.

Public Library of Science2013

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The evolution of lncRNA repertoires and expression patterns in tetrapods

Anamaria Necsulea, Magali Soumillon

Only a very small fraction of long noncoding RNAs (lncRNAs) are well characterized. The evolutionary history of lncRNAs can provide insights into their functionality, but the absence of lncRNA annotations in non-model organisms has precluded comparative analyses. Here we present a large-scale evolutionary study of lncRNA repertoires and expression patterns, in 11 tetrapod species. We identify approximately 11,000 primate-specific lncRNAs and 2,500 highly conserved lncRNAs, including approximately 400 genes that are likely to have originated more than 300 million years ago. We find that lncRNAs, in particular ancient ones, are in general actively regulated and may function predominantly in embryonic development. Most lncRNAs evolve rapidly in terms of sequence and expression levels, but tissue specificities are often conserved. We compared expression patterns of homologous lncRNA and protein-coding families across tetrapods to reconstruct an evolutionarily conserved co-expression network. This network suggests potential functions for lncRNAs in fundamental processes such as spermatogenesis and synaptic transmission, but also in more specific mechanisms such as placenta development through microRNA production.

Nature Publishing Group2014

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Transposable elements (TEs) are DNA sequences able to change position in the genome, and represent more than 40% of mammalian genetic material. TEs can have positive or detrimental effects on the host, being both important motors of evolution and genomic threats, and are associated with diseases such as cancer and diabetes. Growing evidence indicates the host co-opts TEs for its benefit, with examples such as syncytins â genes important for placental formation that derive from TEs. Given their potential damaging role, the host needs to repress TEs, especially during early embryogenesis. KRAB-containing zinc finger proteins (KRAB-ZFPs) are important regulators of TEs, which they repress with their cofactor KAP1. In stem cells, the KRAB/KAP1 complex irreversibly silence TEs and is believed to be dispensable in adult cells. KRAB-ZFPs constitute one of the largest families of transcriptional regulators encoded by higher vertebrates, but functional information is missing for most of its members. To shed light on this important family of transcription factors, we first developed a large-scale functional screen matching murine TEs with their cognate KRAB-ZFP. The screen identified KRAB-ZFP809 as the ligand of its previously mapped DNA target in the murine leukemia virus genome. Our method further singled out two novel KRAB-ZFPs binding to TE sequences, as confirmed by repression and binding assays. One of them, Gm6871, was identified to regulate LINE-1 elements together with KAP1 in embryonic stem cells. KAP1 regulation followed a chronologically conditioned pattern, repressing elements that entered the mouse genome between 5.6 and 3.8 million years ago, suggestive of an evolutionary arms race between host KRAB-ZFPs and TEs. Secondly, we found the paralogs ZFP932 and Gm15446 to bind overlapping but distinguishable subsets of ERVK (endogenous retrovirus K), to repress these elements in embryonic stem cells, and to regulate secondarily the expression of neighboring genes. Furthermore, we uncovered that these KRAB-ZFPs and KAP1 control TEs in adult tissues, in cell culture and in vivo, where they partner up to modulate cellular genes. Our results establish an efficient screening method to identify KRAB-ZFPs DNA targets, opening the way to functional analyses of this major class of transcriptional repressors. Most importantly, our study strongly suggests that KRAB-ZFP genes are not only part of an evolutionary arms race with TEs, but also participate in the domestication of these elements for the benefit of the host. Given the abundance and high degree of species-specificity of TEs and KRAB-ZFPs, these results have important implications for understanding the biology of higher vertebrates, including humans.

EPFL2016

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EPFL2016