IJM News since 2010
Before each cell division, the full genome has to be entirely and faithfully duplicated thereby each daughter cell inherits the complete genetic information. This duplication occurs under the control of a highly sophisticated replication program during the restricted time period corresponding to S phase. DNA replication is initiated at a large number of sites, known as origins of replication, on the chromosomes of eukaryotic cells. In one individual cell, only a part of the origins licensed in G1 phase are activated during S phase thus illustrating the flexible origin choice which is directly related to the stochastic nature of the eukaryotic replication program. Another particularity of the program is that origin activation is also subject to temporal regulation. Like this, some domains of hundred kilobases are replicated in early S phase, others are replicated in mid S phase and the remainders in late S phase. This temporal control is very strict. To date, the factors responsible for the establishment, regulation and maintenance of these domains throughout the cell cycle remain largely unknown. As a first step towards a better comprehension of this temporal program, the team of MN Prioleau has investigated whether the stochasticity of the timing program is changing along the S phase.
Conflicting activities necessary for the expression, the maintenance and the propagation of genomes need to be coordinated. Just like one's liberty to swing fists ends where another's nose begins, coordination is achieved through a tight control of where and when directly opposed activities take place. In a study published recently in eLife, researchers from the Libri team are now showing that replication factors generally "protect" sites where replication initiates by terminating incoming transcription, and that the low levels of transcription that enter origins of replication affect their firing efficiency.
Cell migration is an essential biological process that drives tissue and organ formation during embryo development, and also helps protect the body through immune response and wound healing mechanisms.
What is a transcription factor? Classical biology tells us that a transcription factor binds to a promoter and activates (or represses) gene expression by promoting (or inhibiting) the initiation of transcription. What about transcription factors that activates gene expression by inhibiting initiation?
In an article recently published in P.N.A.S., researchers from the “Regulation of Actin Assembly Dynamics” team at Institut Jacques Monod show how the biochemical disassembly of actin filaments can be modulated by their physical context.
January 2019: Links between polarity protein localization, membrane trafficking and the cytoskeleton
Cellular polarity is an essential characteristic of the development and functioning of an organism. It allows the subdivision of the cell into different functional domains, both at the level of the plasma membrane and the cytoplasm, ensuring asymmetry in the functions of the cell. Establishment and maintenance of cell polarity are under the control of two main well preserved protein modules among metazoans, including PAR1 and PAR3, respectively.
C’est avec un grand regret que nous avons appris le décès le 29 décembre dernier de Jacques Ricard qui fut directeur de l’Institut Jacques Monod de 1992 à 1996 et professeur d’Enzymologie à l’Université Paris-Diderot. Il a été également directeur du Centre de Biochimie et de Biologie Moléculaire du CNRS à Marseille de 1980 à 1991, membre de l’Académie Internationale de Philosophie des Sciences et membre correspondant de l’Académie des Sciences. Nous lui devons en particulier d’avoir structuré l’Institut Jacques Monod en départements, qui fut le mode de fonctionnement jusqu’en 2008 et d’avoir été l’artisan d’une orientation « Biologie cellulaire » forte à l’Institut. Ses travaux ont été fondateurs dans le domaine de l’enzymologie, notamment en ce qui concerne la régulation des enzymes via leurs interactions avec leurs substrats et métabolites ainsi que leur environnement cellulaire.
In an article published in December in eLife, the Dumont team at the Institut Jacques Monod shows that the kinase BUB-1 controls chromosome segregation by modulating the activity of various kinetochore components. Surprisingly, this function of BUB-1 is independent of its kinase activity.
Regeneration, the ability of some animals to restore a lost or damaged body part is a fascinating process that has intrigued biologists since centuries. The annelid Platynereis dumerilii is one such animals possessing remarkable regeneration abilities. This marine worm is indeed able to reform various parts of its body following amputation, notably its appendages and its posterior part. The latter contains both various differentiated structures and stem cells responsible of the growth of the animals. In a paper published this month in Developmental Biology, Anabelle Planques and members of the “Stem cells, Development and Evolution” team at the Institut Jacques Monod, in collaboration with a researcher form the University of Coruña (Spain), characterized Platynereis caudal regeneration. They have shown that posterior regeneration is a very rapid process, requiring cell proliferation and during which several genes, known to be markers of stem cells in various models, are expressed. The origin of the cells involved in regeneration of missing structures has been partly uncovered, suggesting a major role of dedifferentiation of cells abutting the amputation site. This pioneer study of Platynereis regeneration paves the way to the identification of mechanisms controlling this process in this species and open new perspectives for the understanding of its evolution at the metazoan scale.
Male genitals evolve very quickly in animals. Studying the mechanisms underlying their evolution is crucial to understand the phenomenon of speciation. However, the genes involved in genital differences between species are poorly known. A work published in the journal Current Biology in October, resulting from a collaboration between the Jacques Monod Institute, the CNRS, the Paris Museum, the EGCE laboratory of Gif-sur-Yvette and two teams in the United States, constitutes a first step forward in Drosophila. The mutation of a single letter in the DNA contributes to both the loss of sensory organs under the phallus and the increase in size of a sexual comb located on the legs. This is the first time that a single mutation is observed to contribute to the evolution of two organs between species.