The Nercc1 protein kinase autoactivates in vitro and is activated in vivo during mitosis. Autoactivation in vitro requires phosphorylation of the activation loop at threonine 210. Mitotic activation ...of Nercc1 in mammalian cells is accompanied by Thr210 phosphorylation and involves a small fraction of total Nercc1. Mammalian Nercc1 coimmunoprecipitates gamma-tubulin and the activated Nercc1 polypeptides localize to the centrosomes and spindle poles during early mitosis, suggesting that active Nercc has important functions at the microtubular organizing center during cell division. To test this hypothesis, we characterized the Xenopus Nercc1 orthologue (XNercc). XNercc endogenous to meiotic egg extracts coprecipitates a multiprotein complex that contains gamma-tubulin and several components of the gamma-tubulin ring complex and localizes to the poles of spindles formed in vitro. Reciprocally, immunoprecipitates of the gamma-tubulin ring complex polypeptide Xgrip109 contain XNercc. Immunodepletion of XNercc from egg extracts results in delayed spindle assembly, fewer bipolar spindles, and the appearance of aberrant microtubule structures, aberrations corrected by addition of purified recombinant XNercc. XNercc immunodepletion also slows aster assembly induced by Ran-GTP, producing Ran-asters of abnormal size and morphology. Thus, Nercc1 contributes to both the centrosomal and the chromatin/Ran pathways that collaborate in the organization of a bipolar spindle.
A collaborative multi-agent reinforcement learning (RL) problem is considered, where agents communicate over a noisy communication channel towards achieving a common goal. In particular, we consider ...a remote-controlled version of a single-agent RL problem, in which the system state is observed by a guide agent, while the actions are taken by a scout. The guide can communicate to the scout over a noisy communication link, reminiscent of a remote-controlled version of the single-agent RL problem. This transformation turns the original single-agent Markov decision process (MDP) into a two-agent partially observable MDP (POMDP). In conventional systems, communication and learning tasks are taken care of separately. We show the suboptimality of this approach, and propose a deep Q-Iearning solution that aims at learning the optimal policy taking into account the channel impairments.
Echinoderm microtubule-associated protein-like 4 (EML4)–anaplastic lymphoma kinase (ALK) oncogenic fusion proteins are found in approximately 5% of non–small cell lung cancers. Different EML4–ALK ...fusion variants exist with variant 3 (V3) being associated with a significantly higher risk than other common variants, such as variant 1 (V1). Patients with V3 respond less well to targeted ALK inhibitors, have accelerated rates of metastasis, and have poorer overall survival. A pathway has been described downstream of EML4–ALK V3 that is independent of ALK catalytic activity but dependent on the NEK9 and NEK7 kinases. It has been proposed that assembly of an EML4–ALK V3–NEK9–NEK7 complex on microtubules leads to cells developing a mesenchymal-like morphology and exhibiting enhanced migration. However, downstream targets of this complex remain unknown. Here, we show that the microtubule-based kinesin, Eg5, is recruited to interphase microtubules in cells expressing EML4–ALK V3, whereas chemical inhibition of Eg5 reverses the mesenchymal morphology of cells. Furthermore, we show that depletion of NEK7 interferes with Eg5 recruitment to microtubules in cells expressing EML4–ALK V3 and cell length is reduced, but this is reversed by coexpression of a phosphomimetic mutant of Eg5, in a site, S1033, phosphorylated by NEK7. Intriguingly, we also found that expression of Eg5-S1033D led to cells expressing EML4–ALK V1 adopting a more mesenchymal-like morphology. Together, we propose that Eg5 acts as a substrate of NEK7 in cells expressing EML4–ALK V3 and Eg5 phosphorylation promotes the mesenchymal morphology typical of these cells.
The NIMA‐family kinases Nek9/Nercc1, Nek6 and Nek7 form a signalling module required for mitotic spindle assembly. Nek9, the upstream kinase, is activated during prophase at centrosomes although the ...details of this have remained elusive. We now identify Plk1 as Nek9 direct activator and propose a two‐step activation mechanism that involves Nek9 sequential phosphorylation by CDK1 and Plk1. Furthermore, we show that Plk1 controls prophase centrosome separation through the activation of Nek9 and ultimately the phosphorylation of the mitotic kinesin Eg5 at Ser1033, a Nek6/7 site that together with the CDK1 site Thr926 we establish contributes to the accumulation of Eg5 at centrosomes and is necessary for subsequent centrosome separation and timely mitosis. Our results provide a basis to understand signalling downstream of Plk1 and shed light on the role of Eg5, Plk1 and the NIMA‐family kinases in the control of centrosome separation and normal mitotic progression.
Roig and colleagues elucidate the mechanisms of centrosome separation in mammalian cells. Their work reveals essential contributions of the NIMA kinases Nek6/7 and Nek9 downstream of CDK1–Plk1 activity in mitotic cells.
Regulation of the γ-tubulin ring complex (γTuRC) through targeting and activation restricts nucleation of microtubules to microtubule-organizing centers (MTOCs), aiding in the assembly of ordered ...microtubule arrays. However, the mechanistic basis of this important regulation remains poorly understood. Here, we show that, in human cells, γTuRC integrity, determined by the presence of γ-tubulin complex proteins (GCPs; also known as TUBGCPs) 2-6, is a prerequisite for interaction with the targeting factor NEDD1, impacting on essentially all γ-tubulin-dependent functions. Recognition of γTuRC integrity is mediated by MZT1, which binds not only to the GCP3 subunit as previously shown, but cooperatively also to other GCPs through a conserved hydrophobic motif present in the N-termini of GCP2, GCP3, GCP5 and GCP6. MZT1 knockdown causes severe cellular defects under conditions that leave γTuRC intact, suggesting that the essential function of MZT1 is not in γTuRC assembly. Instead, MZT1 specifically binds fully assembled γTuRC to enable interaction with NEDD1 for targeting, and with the CM1 domain of CDK5RAP2 for stimulating nucleation activity. Thus, MZT1 is a 'priming factor' for γTuRC that allows spatial regulation of nucleation.
To study the utility of the virtual combinatorial chemistry coupled with computational screening, a library of amine and urea derivatives was designed by virtual combinatorial synthesis and ...eventually computationally screened by a mathematical topological model as antihistaminic compounds. The results reveal that virtual combinatorial synthesis and virtual screening together with molecular topology are a powerful tool in the design of new drugs.
Resum: La llegenda negra dels Borja va començar a Itàlia i la van començar els italians en el segle XV. Començada a forjar per cronistes, informadors, cardenals… i contràriament al que es podria ...pensar, aquesta no va començar després de la mort del segon papa Borja Alexandre VI, sinó durant el seu cardenalat, el seu pontificat i com no, després de la seua mort i continuant els segles posteriors amb acusacions falses com la simonia, el incest, els assassinats… Paraules clau: Borja, Roderic de Borja, Alexandre VI, llegenda negra, Bichi, Tiara, papa, conclave, simonia, Ascanio Sforza. Abstract: The black legend of Borja began in Italy and Italians began in the fifteenth century. Created by reporters, cardinals ... and contrary to what you might think, not this black legend began after the death of the second Pope Alexander VI Borja but the cardinal time, and of his pontificate, after his death and continue over the following centuries with false accusations as simony, the incest, murder … Keywords: Borja, Roderic de Borja, Pope Alexander VI, black legend, Bichi, Tiara, Pope conclave, simony, Ascanio Sforza.
The γ-tubulin complex is a multi-subunit protein complex that nucleates microtubule polymerization. γ-Tubulin complexes are present in all eukaryotes, but size and subunit composition vary. In ...Drosophila, Xenopus, and humans large γ-tubulin ring complexes (γTuRCs) have been described, which have a characteristic open ring-shaped structure and are composed of a similar set of subunits, named γ-tubulin, GCPs 2-6, and GCP-WD in humans. Despite the identification of these proteins, γTuRC function and regulation remain poorly understood. Here we establish a new method for the purification of native human γTuRC. Using mass spectrometry of whole protein mixtures we compared the composition of γTuRCs from nonsynchronized and mitotic human cells. Based on our analysis we can define core subunits as well as more transient interactors such as the augmin complex, which associates specifically with mitotic γTuRCs. We also identified GCP8/MOZART2 as a novel core subunit that is present in both interphase and mitotic γTuRCs. GCP8 depletion does not affect γTuRC assembly but interferes with γTuRC recruitment and microtubule nucleation at interphase centrosomes without disrupting general centrosome structure. GCP8-depleted cells do not display any obvious mitotic defects, suggesting that GCP8 specifically affects the organization of the interphase microtubule network.
We propose a novel formulation of the "effectiveness problem" in communications, put forth by Shannon and Weaver in their seminal work 2, by considering multiple agents communicating over a noisy ...channel in order to achieve better coordination and cooperation in a multi-agent reinforcement learning (MARL) framework. Specifically, we consider a multi-agent partially observable Markov decision process (MA-POMDP), in which the agents, in addition to interacting with the environment can also communicate with each other over a noisy communication channel. The noisy communication channel is considered explicitly as part of the dynamics of the environment and the message each agent sends is part of the action that the agent can take. As a result, the agents learn not only to collaborate with each other but also to communicate "effectively" over a noisy channel. This framework generalizes both the traditional communication problem, where the main goal is to convey a message reliably over a noisy channel, and the "learning to communicate" framework that has received recent attention in the MARL literature, where the underlying communication channels are assumed to be error-free. We show via examples that the joint policy learned using the proposed framework is superior to that where the communication is considered separately from the underlying MA-POMDP. This is a very powerful framework, which has many real world applications, from autonomous vehicle planning to drone swarm control, and opens up the rich toolbox of deep reinforcement learning for the design of multi-user communication systems.
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