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Ronsseray S.,CNRS Developmental Biology Laboratory
Seminars in Cell and Developmental Biology | Year: 2015

Paramutation was initially described in maize and was defined as an epigenetic interaction between two alleles of a locus, through which one allele induces a heritable modification of the other allele without modifying the DNA sequence [1,2]. Thus it implies that the paramutated allele conserves its new properties on the long term over generations even in the absence of the paramutagenic allele and that it turns paramutagenic itself, without undergoing any changes in the DNA sequence. Some epigenetic interactions have been described in two non-vertebrate animal models, which appear to exhibit similar properties. Both systems are linked to trans-generational transmission of non-coding small RNAs. In Drosophila melanogaster, paramutation is correlated with transmission of PIWI-Interacting RNAs (piRNAs), a class of small non-coding RNAs that repress mobile DNA in the germline. A tandem repeated transgenic locus producing abundant ovarian piRNAs can activate piRNA production and associated homology-dependent silencing at a locus that was previously stably devoid of such capacities. The newly converted locus is then perfectly stable in absence of the inducer locus (>100 generations) and becomes fully paramutagenic. In Caenorhabditis elegans, paramutation is correlated with transmission of siRNAs, which are produced by transgenes targeted by piRNAs in the germline. Indeed, a transgenic locus, targeted by the piRNA machinery, produces siRNAs that can induce silencing of homologous transgenes, which can be further transmitted in a repressed state over generations despite the absence of the inducer transgenic locus. As in fly, the paramutated locus can become fully paramutagenic, and paramutation can be mediated by cytoplasmic inheritance without transmission of the paramutagenic locus itself. Nevertheless, in contrast to flies where the induction is only maternally inherited, both parents can transmit it in worms. In addition, a reciprocal phenomenon - (from off toward on) - appears to be also possible in worms as some activated transgenes can reactivate silent transgenes in the germline, and this modification can also be transmitted to next generations, even so it appears to be only partially stable. Thus, in a given system, opposite paramutation-like phenomena could exist, mediated by antagonist active pathways. As in plants, paramutation in flies and worms correlates with chromatin structure modification of the paramutated locus. In flies, inheritance of small RNAs from one generation to the next transmits a memory mainly targeting loci for repression whereas in worms, small RNAs can target loci either for repression or expression. Nevertheless, in the two species, paramutation can play an important role in the epigenome establishment. © 2015 Elsevier Ltd.

Crozatier M.,CNRS Developmental Biology Laboratory | Vincent A.,CNRS Developmental Biology Laboratory
DMM Disease Models and Mechanisms | Year: 2011

Vertebrate haematopoietic stem cells (HSCs) give rise to a hierarchically organised set of progenitors for erythroid, myeloid, lymphoid and megakaryocyte lineages, and are responsible for lifelong maintenance of the blood system. Dysregulation of the haematopoietic differentiation programme is at the origin of numerous pathologies, including leukaemias. With the discoveries that many transcriptional regulators and signalling pathways controlling blood cell development are conserved between humans and Drosophila melanogaster, the fruit fly has become a good model for investigating the mechanisms underlying the generation of blood cell lineages and blood cell homeostasis. In this review article, we discuss how genetic and molecular studies of Drosophila haematopoiesis can contribute to our understanding of the haematopoietic niche, as well as of the origin and/or progression of haematopoietic malignancies in humans. © 2011. Published by The Company of Biologists Ltd.

In this review we present concepts that challenge a recently emerging paradigm explaining how similar Hox proteins perform different developmental functions across evolution, despite relatively limited sequence variability. This paradigm relates to the transcription factor, Fushi tarazu (Ftz), whose evolutionary plasticity has been shown to rely on the shuffling between two short protein recognition motifs. We discuss the Ftz paradigm and consider alternative interpretations to the evolutionary flexibility of this Hox protein. In particular, we propose that the protein environment might have played a critical role in the functional shuffling of Ftz during arthropod evolution. © 2011 WILEY Periodicals, Inc.

Nourissat G.,Service de chirurgie orthopedique et traumatologique | Berenbaum F.,Service de Rhumatologie | Duprez D.,CNRS Developmental Biology Laboratory
Nature Reviews Rheumatology | Year: 2015

Tendon is a crucial component of the musculoskeletal system. Tendons connect muscle to bone and transmit forces to produce motion. Chronic and acute tendon injuries are very common and result in considerable pain and disability. The management of tendon injuries remains a challenge for clinicians. Effective treatments for tendon injuries are lacking because the understanding of tendon biology lags behind that of the other components of the musculoskeletal system. Animal and cellular models have been developed to study tendon-cell differentiation and tendon repair following injury. These studies have highlighted specific growth factors and transcription factors involved in tenogenesis during developmental and repair processes. Mechanical factors also seem to be essential for tendon development, homeostasis and repair. Mechanical signals are transduced via molecular signalling pathways that trigger adaptive responses in the tendon. Understanding the links between the mechanical and biological parameters involved in tendon development, homeostasis and repair is prerequisite for the identification of effective treatments for chronic and acute tendon injuries. © 2015 Macmillan Publishers Limited. All rights reserved.

Wassmann K.,University Pierre and Marie Curie | Wassmann K.,CNRS Developmental Biology Laboratory
Cell Cycle | Year: 2013

Meiotic divisions (meiosis I and II ) are specialized cell divisions to generate haploid gametes. The first meiotic division with the separation of chromosomes is named reductional division. The second division, which takes place immediately after meiosis I without intervening S-phase, is equational, with the separation of sister chromatids, similar to mitosis. This meiotic segregation pattern requires the two-step removal of the cohesin complex holding sister chromatids together: cohesin is removed from chromosome arms that have been subjected to homologous recombination in meiosis I and from the centromere region in meiosis II . Cohesin in the centromere region is protected from removal in meiosis I, but this protection has to be removed-deprotected-for sister chromatid segregation in meiosis II . Whereas the mechanisms of cohesin protection are quite well understood, the mechanisms of deprotection have been largely unknown until recently. In this review I summarize our current knowledge on cohesin deprotection. © 2013 Landes Bioscience.

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