Littérature scientifique sur le sujet « Mud/NuMA »

Mitotic spindle orientation must be tightly regulated during development and adult tissue homeostasis. It determines cell-fate specification and tissue architecture during asymmetric and symmetric cell division, respectively. Here, we uncover a novel role for Ephrin–Eph intercellular signaling in controlling mitotic spindle alignment in Drosophila optic lobe neuroepithelial cells through aPKC activity–dependent myosin II regulation. We show that conserved core components of the mitotic spindle orientation machinery, including Discs Large1, Mud/NuMA, and Canoe/Afadin, mislocalize in dividing Eph mutant neuroepithelial cells and produce spindle alignment defects in these cells when they are down-regulated. In addition, the loss of Eph leads to a Rho signaling–dependent activation of the PI3K–Akt1 pathway, enhancing cell proliferation within this neuroepithelium. Hence, Eph signaling is a novel extrinsic mechanism that regulates both spindle orientation and cell proliferation in the Drosophila optic lobe neuroepithelium. Similar mechanisms could operate in other Drosophila and vertebrate epithelia.

ABSTRACT. Muds of different compositions are used in the drilling well process, to support the wall of the borehole along with maintenance of pressure, and toremove rock cuttings generated from the geological formations encountered by the drill bit. The drilling mud invades the formations and modifies the zones surroundingthe borehole, mainly, in terms of the physical properties of the rocks, such as porosity and permeability. The identification of this formation damage is important forreservoir characterization, and the subsequent well completion, as well as for the analysis of economic viability. Many years ago, Schlumberger developed a methodfor determining mud invasion diameter using the Tornado Chart. Today, practitioners in the oil industry use the Tornado Chart to present geophysical logs. Improvingupon Schlumberger’s methodology, Crain used mathematical equations to calculate the mud invasion diameter. In this study, we propose a polynomial mathematicalmethod to determine mud invasion diameter. Our method utilizes the same resistivity well logs, namely dual induction log and dual laterology, though different from thatof Schlumberger or Crain methods. The approach developed in this study considers the characteristics of the invasion process while quickly and accurately showingresults in the form of a log that can be visualized adjacent to other logs measured in the borehole.Keywords: formation damage, drilling mud invasion, resistivity well logs. RESUMO. No processo de perfuração de poços são utilizadas diferentes composições de lama com o propósito de suportar a parede do poço, manter a pressão e, ainda, remover os fragmentos de rocha originados pela broca ao atravessar as formações geológicas. A lama de perfuração invade as formações e modifica as zonas circundantes ao poço, sobretudo, em termos das propriedades físicas das rochas, tais como a porosidade e permeabilidade. A identificação deste tipo de dano à formação é importante, principalmente para a caracterização do reservatório, bem como nas atividades posteriores de conclusão do poço e, ainda, na análise deviabilidade econômica. Neste sentido, há muitos anos, a Schlumberger desenvolveu uma maneira de determinar o diâmetro de invasão da lama usando o GráficoTornado, que é utilizado até hoje na indústria do petróleo, essencialmente usando perfis geofísicos. Mais tarde, com o objetivo de melhorar a determinação do diâmetro de invasão, Crain usou equações matemáticas para calcular esse valor, fazendo correções na metodologia da Schlumberger. Neste trabalho, por outro lado, propõe-se um método matemático polinomial para determinar o diâmetro de invasão, que é diferente das metodologias desenvolvidas pela Schlumberger e por Crain, mas também utilizando os mesmos perfis resistivos de poços, ou seja, os perfis de indução (DIL) e laterolog (DLL) duplos. Desta forma, o procedimento desenvolvido no presentetrabalho mostrou-se rápido e preciso, pois considera melhor as características do processo de invasão, mostrando ainda os resultados sob a forma de um perfil ao lado de outros perfis medidos no poço, resultando, assim, numa visualização mais eficiente.Palavras-chave: dano à formação, invasão da lama de perfuração, perfis resistivos de poços.

Proper positioning of the mitotic spindle is fundamental for specifying the site for cleavage furrow, and thus regulates the appropriate sizes and accurate distribution of the cell fate determinants in the resulting daughter cells during development and in the stem cells. The past couple of years have witnessed tremendous work accomplished in the area of spindle positioning, and this has led to the emergence of a working model unravelling in-depth mechanistic insight of the underlying process orchestrating spindle positioning. It is evident now that the correct positioning of the mitotic spindle is not only guided by the chemical cues (protein–protein interactions) but also influenced by the physical nature of the cellular environment. In metazoans, the key players that regulate proper spindle positioning are the actin-rich cell cortex and associated proteins, the ternary complex (Gα/GPR-1/2/LIN-5 in Caenorhabditis elegans, Gαi/Pins/Mud in Drosophila and Gαi1-3/LGN/NuMA in humans), minus-end-directed motor protein dynein and the cortical machinery containing myosin. In this review, I will mainly discuss how the abovementioned components precisely and spatiotemporally regulate spindle positioning by sensing the physicochemical environment for execution of flawless mitosis.

The microtubule spindle apparatus dictates the plane of cell cleavage in animal cells. During development, dividing cells control the position of the spindle to determine the size, location, and fate of daughter cells. Spindle positioning depends on pulling forces that act between the cell periphery and astral microtubules. This involves dynein recruitment to the cell cortex by a heterotrimeric G-protein α subunit in complex with a TPR-GoLoco motif protein (GPR-1/2, Pins, LGN) and coiled-coil protein (LIN-5, Mud, NuMA). In this study, we searched for additional factors that contribute to spindle positioning in the one-cell Caenorhabditis elegans embryo. We show that cortical actin is not needed for Gα–GPR–LIN-5 localization and pulling force generation. Instead, actin accumulation in the anterior actually reduces pulling forces, possibly by increasing cortical rigidity. Examining membrane-associated proteins that copurified with GOA-1 Gα, we found that the transmembrane and coiled-coil domain protein 1 (TCC-1) contributes to proper spindle movements. TCC-1 localizes to the endoplasmic reticulum membrane and interacts with UNC-116 kinesin-1 heavy chain in yeast two-hybrid assays. RNA interference of tcc-1 and unc-116 causes similar defects in meiotic spindle positioning, supporting the concept of TCC-1 acting with kinesin-1 in vivo. These results emphasize the contribution of membrane-associated and cortical proteins other than Gα–GPR–LIN-5 in balancing the pulling forces that position the spindle during asymmetric cell division.

Asymmetric cell division (ACD) allows stem cells to generate differentiating progeny while simultaneously maintaining their own pluripotent state. ACD involves coupling mitotic spindle orientation with cortical polarity cues to direct unequal segregation of cell fate determinants. In Drosophila neural stem cells (neuroblasts; NBs), spindles orient along an apical-basal polarity axis through a conserved complex of Partner of Inscuteable (Pins; human LGN) and Mushroom body defect (Mud; human NuMA). While many details of its function are well known, the molecular mechanics that drive assembly of the cortical Pins/Mud complex remain unclear, particularly with respect to the mutually exclusive Pins complex formed with the apical scaffold protein Inscuteable (Insc). Here we identify Hu li tai shao (Hts; human Adducin) as a direct Mud-binding protein, using an aldolase fold within its head domain (HtsHEAD) to bind a short Mud coiled-coil domain (MudCC) that is adjacent to the Pins-binding domain (MudPBD). Hts is expressed throughout the larval central brain and apically polarizes in mitotic NBs where it is required for Mud-dependent spindle orientation. In vitro analyses reveal that Pins undergoes liquid-liquid phase separation with Mud, but not with Insc, suggesting a potential molecular basis for differential assembly mechanics between these two competing apical protein complexes. Furthermore, we find that Hts binds an intact Pins/Mud complex, reduces the concentration threshold for its phase separation, and alters the liquid-like property of the resulting phase separated droplets. Domain mapping and mutational analyses implicate critical roles for both multivalent interactions (via MudCC oligomerization) and protein disorder (via an intrinsically disordered region in Hts; HtsIDR) in phase separation of the Hts/Mud/Pins complex. Our study identifies a new component of the spindle positioning machinery in NBs and suggests that phase separation of specific protein complexes might regulate ordered assembly within the apical domain to ensure proper signaling output.

Durant une division asymétrique (ACD), cycle et polarité cellulaires se coordonnent pour servir la diversité cellulaire. Dans le cas d’une ACD au sein d‘un épithélium, la Polarité Cellulaire Planaire, menée par Frizzled (Fz) et Dishevelled (Dsh), oriente la cellule mère et le fuseau mitotique et induit une polarité qui va permettre l’alignement et la répartition des déterminants cellulaires entre les cellules filles. Dans ce contexte, mon sujet de thèse vise à étudier les liens entre cycle et polarité dans le modèle du lignage des soies de la drosophile, où depuis l’ACD de la cellule précurseur pI, quatre destins cellulaires distincts émergent. À chaque division, la voie Notch est différentiellement activée et la PCP régule les orientations stéréotypées des divisions dans le plan de l’épithélium. Au sein de la division de la cellule pI, j’ai pu mettre en exergue que l’un des acteurs majeurs du cycle cellulaire, la Cycline A faisait ce lien. En effet, j’ai observé qu’une portion de Cycline A se localisait asymétriquement au cortex apical postérieur de pI en prophase. Cette portion de Cycline A est dégradée en même temps que la potion cytoplasmique. Ensuite j’ai montré que Cycline A colocalisait avec les facteurs de la PCP, Fz et Dsh, que ceux-ci lui servaient d’ancre au cortex : la perte de fonction dsh ou fz empêche le recrutement de Cycline A au cortex et la délocalisation forcée de Frizzled entraine aussi celle de Cycline A. Aussi, Cycline A influence sur l’orientation du fuseau mitotique comme Frizzled et Dsh par la perte de fonction cycline A ou l’expression d’une Cycline A ectopique au cortex. Ceci suggère que Cycline A fait partie du complexe formé par Fz et Dsh régulant l’orientation du fuseau. Ce rôle dans l’orientation de la division a été montré par un le recrutement au cortex apical postérieur de la protéine Mud (NuMA/LIN-5). Ce travail de thèse ouvre la porte sur les rôles encore peu connus des facteurs de cycle dans d’autres processus biologiques
During an asymmetric cell division (ACD), the cell cycle and cell proliferation are coordinated to serve cell fate diversity. In the case of an ACD occurring in epithelia, the Planar Cell Polarity, lead by Frizzled (Fz) and Dishevelled (Dsh) orients the mother cell and the mitotic spindle to induce a polarity upon which the cell fate determinants are asymmetrically divided between the daughter cells. In this context, my thesis subject relies on the study of the links between cell cycle and cell polarity in the model of the lineage of mecanosensory organs of Drosophila, from which four distinct cell fates rise. At each division, the Notch pathway is asymmetrically activated and the PCP regulates the stereotyped orientations of the divisions along the epithelial plan. During the ACD of the pI cell, I have shown that one of these links was the major actor the cell cycle Cyclin A. Indeed, I have shown that a pool of Cyclin A localises asymmetrically the apical posterior cortex of the pi cell during prophase. This portion of Cyclin A is degraded at the same time of the cytoplasmic pool. Then, I have shown that Cyclin A co-localised with the PCP factor Fz and Dsh, as they anchors CycA to the cortex: a fz or dsh loss of function (LOF) abolishes the cortical recruitment of Cyclin A and the delocalisation of Frizzled drags Cyclin A. More importantly, I have shown that Cyclin A also regulates the orientation of the division as PCP factors, as its LOF or ectopic cortical localisation deviated the orientation. Altogether this data suggest that Cyclin A is part of complex regulating the spindle orientation formed by Fz and Dsh. In order to do so, Cyclin A is required for the apical posterior recruitment of the Mud protein (NuMA/LIN-5). This work opens the door on the roles, poorly described, of the cells cycle factors in other biological processes