Identifiabilité structurelle et identification de systèmes couplés par les sorties

International audienceCet article s'intéressè a l'identification des syst emes de grande taille qui peuvent etre décomposés en une collection de sous-syst emes couplés par les sorties. Il est d'abord montré que si le syst eme global est structurellement identifiable, alors tous les sous-syst emes le sont egalement, en considérant les sorties comme de nouvelles entrées. Cette propriété est ensuite utilisée pour proposer une procédure d'identification décentralisée. L'efficacité de l'approche pro-posée est illustrée sur un exemple académique. Mots-clés— Identifiabilité structurelle, Identification décen-tralisée, Syst emes de grande taille. I. Introduction Les syst emes technologiques de grande taille tels que les syst emes de transport, les syst emes electriques, les syst emes de bâtiments. . .sont omniprésents dans notre vie moderne. La grande taille de ces syst emes a conduit au développement de diverses techniques pour réduire la complexité de leur etude. Une approche possible est de considérer le grand syst eme comme une collection de nom-breux sous-syst emes plus simples. L'identification [1] est un point crucial pour l'´ elaboration d'une stratégie de contrôle basée sur un mod ele. D'un point de vue pratique, leprobì eme de la taille des syst emes se posé egalement pour l'identification paramétrique. Pour simplifier l'identification des syst emes de grande taille, de nombreux auteurs ont essayé d'exploiter leur structure. Dans [5], le syst eme global est hiérarchisé et une méthode itérative est proposée pour l'identification. Dans [7], les auteurs s' intéressent aux syst emes circulants [3], et ils exploitent leurs propriétés pour définir une procédure originale d'identification. Une autre technique exploite la propriété de découplage en boucle fermée afin de définir une collection d'observateurs décentralisés pour les syst emes non linéaires interconnectés [12]. Dans cet article, nous supposons que le syst eme global est structurellement identifiable. L'identifiabilité structu-relle est une propriété importante quand il faut evaluer les param etres du syst eme, car elle garantit l'unicité des param etres [15]. Dans [13], l'auteur se concentre sur les syst emes compartimentaux pour etudier l'identifiabi-lité structurelle du syst eme global, et dans [4], l'identi-fiabilité pratique peut etre vérifiée pour des conditions suffisantes sur les signaux d'interaction entre les sous-syst emes. Dans ce document, on consid ere un ensemble de syst emes linéaires couplés par leurs sorties. Un exemple est représenté sur la figure 1. De nombreux processus peuvent etre modélisés sous cette forme, c'est le cas par exemple des syst emes thermiques dans les bâtiments [8]

Wood Utilization Is Dependent on Catalase Activities in the Filamentous Fungus Podospora anserina

Catalases are enzymes that play critical roles in protecting cells against the toxic effects of hydrogen peroxide. They are implicated in various physiological and pathological conditions but some of their functions remain unclear. In order to decipher the role(s) of catalases during the life cycle of Podospora anserina, we analyzed the role of the four monofunctional catalases and one bifunctional catalase-peroxidase genes present in its genome. The five genes were deleted and the phenotypes of each single and all multiple mutants were investigated. Intriguingly, although the genes are differently expressed during the life cycle, catalase activity is dispensable during both vegetative growth and sexual reproduction in laboratory conditions. Catalases are also not essential for cellulose or fatty acid assimilation. In contrast, they are strictly required for efficient utilization of more complex biomass like wood shavings by allowing growth in the presence of lignin. The secreted CATB and cytosolic CAT2 are the major catalases implicated in peroxide resistance, while CAT2 is the major player during complex biomass assimilation. Our results suggest that P. anserina produces external H2O2 to assimilate complex biomass and that catalases are necessary to protect the cells during this process. In addition, the phenotypes of strains lacking only one catalase gene suggest that a decrease of catalase activity improves the capacity of the fungus to degrade complex biomass

MRCK controls myosin II activation in the polarized cortex of mouse oocytes and promotes spindle rotation and male pronucleus centration

Abstract Asymmetric meiotic divisions in oocytes rely on spindle positioning in close vicinity to the cortex. In mouse oocytes arrested at metaphase II, eccentric spindle positioning is associated with a chromatin-induced remodeling of the overlying cortex, including the build-up of an actin cap surrounded by a ring of activated myosin II. While the role of the actin cap in promoting polar body formation was demonstrated, the role of ring myosin II, and its mechanism of activation, have remained elusive. Here, we show that ring myosin II activation requires Myotonic dystrophy kinase-Related Cdc42-binding Kinase (MRCK), downstream of polarized Cdc42. During anaphase-II, inhibition of MRCK resulted in spindle rotation defects and a decreased rate of polar body emission. Remarkably, some oocytes eventually achieved spindle rotation by disengaging one cluster of chromatids from the anaphase spindle. We show that the MRCK/myosin II pathway also regulates the flattening of the fertilization cone to initiate male pronucleus centration. These findings provide novel insights into mammalian oocyte polarization and the role of cortical myosin II in orchestrating asymmetric division

Polar Body Formation After Ovulation and Fertilization

International audienceIn sexual reproduction, male and female gametes unite at fertilization, to generate a genetically unique individual, which combines both parental genomes. Instrumental to the success of embryo development is the haploidization of the parental genomes, so as to restore a diploid chromosome complement after gamete fusion. Meiosis is the process by which haploid gametes (i.e., in which each chromosome is present as a single copy) are generated from diploid parental germ cells (in which each chromosome is present as two copies). In addition, paternal and maternal homologous chromosomes exchange segments of DNA during meiosis, creating genetic diversity. In oocyte meiosis, haploidization is achieved via a succession of two asymmetric divisions, to produce a big egg, and two small daughter cells called polar bodies, in which supernumerary chromosomes are discarded. The fertilized egg will develop into an embryo, while polar bodies will eventually degenerate. In the great majority of mammalian species studied so far, including human, the first meiotic division is achieved shortly before ovulation. Hence, the ovulated egg has emitted the first polar body. Emission of the second polar body, a hallmark of meiosis completion, requires the egg to be fertilized.In this article, we review the basic principles of polar body formation in the mammalian fertilized egg, and we introduce the concept of cortical polarization, a prerequisite for polar body formation. The results and concepts presented here are based essentially on studies realized with eggs from mammalian species, mostly mouse.</div

MRCK activates mouse oocyte myosin II for spindle rotation and male pronucleus centration

International audienceAsymmetric meiotic divisions in oocytes rely on spindle positioning in close vicinity to the cortex. In metaphase-II mouse oocytes, eccentric spindle positioning triggers cortical polarization, including the build-up of an actin cap surrounded by a ring of activated myosin II. While the role of the actin cap in promoting polar body formation is established, ring myosin II activation mechanisms and functions have remained elusive. Here, we show that ring myosin II activation requiresMyotonic dystrophy kinase-Related Cdc42-binding Kinase (MRCK), downstream of polarized Cdc42. MRCK inhibitionresulted in spindle rotation defects during anaphase-II, precluding polar body extrusion. Remarkably, disengagement ofsegregated chromatid from the anaphase spindle could rescue rotation. We further show that the MRCK/myosin II pathwayis activated in the fertilization cone and is required for male pronucleus migration toward the center of the zygote. Thesefindings provide novel insights into the mechanism of myosin II activation in oocytes, and its role in orchestrating asymmetric division and pronucleus centration

Cofilin regulates actin network homeostasis and microvilli length in mouse oocytes.

How multiple actin networks coexist in a common cytoplasm, while competing for a shared pool of monomers, is still an ongoing question. This is exemplified by meiotic maturation in the mouse oocyte, which relies on the dynamic remodeling of distinct cortical and cytoplasmic F-actin networks. Here we show that the conserved actin-depolymerizing factor cofilin is activated in a switch-like manner at meiosis resumption from prophase arrest. Interfering with cofilin activation during maturation resulted in widespread microvilli elongation, while cytoplasmic F-actin was depleted, leading to defects in spindle migration and polar body extrusion. In contrast, cofilin inactivation in metaphase II-arrested oocytes resulted in a shutdown of F-actin dynamics, along with a dramatic overgrowth of the polarized actin cap. However, inhibition of the Arp2/3 complex to promote actin cap disassembly elicited ectopic microvilli outgrowth in the polarized cortex. These data establish cofilin as a key player in actin network homeostasis in oocytes, and reveal that microvilli can act as a sink for monomers upon disassembly of a competing network

Preservation of structural identifiability in expanded systems

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Age at immigration and the intergenerational income mobility of the 1.5 generation

In this paper, we exploit intergenerationally-linked tax files and Census data to first document the intergenerational income transmission between individuals who immigrated to Canada as children-the 1.5 generation-and their parents. We find that the correlation between parental income rank and child income rank becomes stronger the older the child is at arrival. We then try to get at the causal effect of the age at immigration by estimating a model in which child rank is explained by interactions between age at arrival and the average predicted rank of second-generation immigrants from the same region of origin, living in the same region in Canada, from the same birth cohort, given their parental income. The model gives us the rate at which children from the 1.5 generation catch up to second-generation immigrants. We find that up to age 10, the relation between age at immigration and income is flat, but starting at age 11, each year is associated with 3.3 fewer percentile ranks

Structural Identifiability and Identification of Systems under Output Couplings

International audienceThis paper deals with the identification of large-scale systems that can be decom- posed into a collection of subsystems that are coupled by their outputs. It is first shown that if the global system is structurally identifiable, then all the subsystems are also structurally identifiable considering the coupling outputs as new inputs. This property is then used to propose a decentralized identification procedure. The eficiency of the proposed approach is emphasized on an academical example