Isabelle Vernos: Motoring around the mitotic spindle

Vernos uses cutting-edge microscopy to track spindle assembly in Xenopus eggs

Allosteric inhibition of Aurora-A kinase by a synthetic vNAR domain

The vast majority of clinically-approved protein kinase inhibitors target the ATP binding pocket directly. Consequently, many inhibitors have broad selectivity profiles and most have significant off-target effects. Allosteric inhibitors are generally more selective, but are difficult to identify because allosteric binding sites are often unknown or poorly characterized. Aurora-A is activated through binding of TPX2 to an allosteric site on the kinase catalytic domain, and this knowledge could be exploited to generate an inhibitor. Here, we generated an allosteric inhibitor of Aurora-A kinase based on a synthetic, vNAR single domain scaffold, vNAR-D01. Biochemical studies and a crystal structure of the Aurora-A/vNAR-D01 complex show that the vNAR domain stabilizes an inactive conformation, in which the αC-helix is distorted, the canonical Lys-Glu salt bridge is broken, and the regulatory (R-) spine is disrupted by an additional hydrophobic side chain from the activation loop. These studies illustrate how single domain antibodies can be used to characterize the regulatory mechanisms of kinases and provide a rational basis for structure-guided design of allosteric Aurora-A kinase inhibitors

Regulation of Op18 during Spindle Assembly in Xenopus Egg Extracts

Oncoprotein 18 (Op18) is a microtubule-destabilizing protein that is negatively regulated by phosphorylation. To evaluate the role of the three Op18 phosphorylation sites in Xenopus (Ser 16, 25, and 39), we added wild-type Op18, a nonphosphorylatable triple Ser to Ala mutant (Op18-AAA), and to mimic phosphorylation, a triple Ser to Glu mutant (Op18-EEE) to egg extracts and monitored spindle assembly. Op18-AAA dramatically decreased microtubule length and density, while Op18-EEE did not significantly affect spindle microtubules. Affinity chromatography with these proteins revealed that the microtubule-destabilizing activity correlated with the ability of Op18 to bind tubulin. Since hyperphosphorylation of Op18 is observed upon addition of mitotic chromatin to extracts, we reasoned that chromatin-associated proteins might play a role in Op18 regulation. We have performed a preliminary characterization of the chromatin proteins recruited to DNA beads, and identified the Xenopus polo-like kinase Plx1 as a chromatin-associated kinase that regulates Op18 phosphorylation. Depletion of Plx1 inhibits chromatin-induced Op18 hyperphosphorylation and spindle assembly in extracts. Therefore, Plx1 may promote microtubule stabilization and spindle assembly by inhibiting Op18

The C-terminal domain of TPX2 is made of alpha-helical tandem repeats

Background: TPX2 (Targeting Protein for Xklp2) is essential for spindle assembly, activation of the mitotic kinase Aurora A and for triggering microtubule nucleation. Homologs of TPX2 in Chordata and plants were previously identified. Currently, proteins of the TPX2 family have little structural information and only small parts are covered by defined protein domains. Methods: We have used computational sequence analyses and structural predictions of proteins of the TPX2 family, supported with Circular Dichroism (CD) measurements. Results: Here, we report our finding that the C-terminal domain of TPX2, which is responsible of its microtubule nucleation capacity and is conserved in all members of the family, is actually formed by tandem repeats, covering well above 2/3 of the protein. We propose that this region forms a flexible solenoid involved in protein-protein interactions. Structural prediction and molecular modeling, combined with Circular Dichroism (CD) measurements reveal a predominant alpha-helical content. Furthermore, we identify full length homologs in fungi and shorter homologs with a different domain organization in diptera (including a paralogous expansion in Drosophila). Conclusions: Our results, represent the first computational and biophysical analysis of the TPX2 proteins family and help understand the structure and evolution of this conserved protein family to direct future structural studies

American legal discourse on child trafficking: the re/production of inequalities and persistence of child criminalization

The criminalization of children commercially-sexually exploited through prostitution persists despite trafficking laws recognizing this as one of the worst forms of exploitation committed against the most vulnerable social group. This thesis examines the re/production of inequalities in American legal discourse on child trafficking, and why child criminalization persists in this context. Employing a child-centered framework built from multi-conscious feminism and the sociologies of law and childhood, it examines mechanisms of othering and criminalization in key legislative debates, statutes and cases of the United States generally as well as two states exemplifying the retributive and child-protective modes of handling child trafficking. It identifies three themes or issues often presented as binaries that structure child trafficking discourse—adult/child, victim/offender and consent/non-consent—and examines how these are deployed to penalize children in general, and minority and immigrant children in particular. First, processes of marginalization related to race, class, gender and immigration have been vital to the construction of childhood (as normative/deviant) in and through trafficking and prostitution laws, which are reproduced through different types of discourses in both states. Second, both retributive and child-protective modes of response preserve child criminalization by maintaining the tension between prostitution and trafficking, and the female culpability associated with prostitution, including through the denial of the victimization of “repeat offenders.” Finally, despite its prohibition, prostitution is conceptualized in contractual terms, which imputes consent to identities constructed through this discourse and renders commercial-sexual exploitation as merely or primarily involving acts of sale, purchase and consumption

The chaperonin CCT controls T cell receptor-driven 3D configuration of centrioles

T lymphocyte activation requires the formation of immune synapses (IS) with antigen-presenting cells. The dynamics of membrane receptors, signaling scaffolds, microfilaments, and microtubules at the IS determine the potency of T cell activation and subsequent immune response. Here, we show that the cytosolic chaperonin CCT (chaperonin-containing TCP1) controls the changes in reciprocal orientation of the centrioles and polarization of the tubulin dynamics induced by T cell receptor in T lymphocytes forming an IS. CCT also controls the mitochondrial ultrastructure and the metabolic status of T cells, regulating the de novo synthesis of tubulin as well as posttranslational modifications (poly-glutamylation, acetylation, ?1 and ?2) of ??-tubulin heterodimers, fine-tuning tubulin dynamics. These changes ultimately determine the function and organization of the centrioles, as shown by three-dimensional reconstruction of resting and stimulated primary T cells using cryo-soft x-ray tomography. Through this mechanism, CCT governs T cell activation and polarity.Cryo-SXT work was supported by ALBA Synchrotron standard proposals 2015021148 and 2016021638 to F.J.C., N.B.M.-C., and J.M.V. This study was supported by grants SAF2017-82886-R (to F.S.-M.), PID2019-105872GB-I00/AEI/10.13039/501100011033 (AEI/FEDER, UE), BFU2016-75984 (to J.M.V.), and BIO2015-67580-P and PGC2018-097019-B-I00 (to J.V.) from the Spanish Ministry of Economy and Competitiveness (MINECO), grants INFLAMUNE-S2017/BMD-23671 (to F.S.-M.) and P2018/NMT-4389 (to J.M.V.) from the Comunidad de Madrid, ERC-2011-AdG 294340-GENTRIS (to F.S.-M.), a 2019 grant from the Ramón Areces Foundation “Ciencias de la Vida y la Salud” and a 2018 grant from Ayudas Fundación BBVA a Equipos de Investigación Científica (to F.S.-M.), and grants PRB3 (IPT17/0019-ISCIII-SGEFI/ERDF), the Fundació Marató TV3 (grant 122/C/2015), and “La Caixa” Banking Foundation (HR17-00016 to FSM and HR17-00247 to J.V.). D.T. is supported by a PhD fellowship from La Caixa Foundation. Work in the Vernos lab was supported by the grant CSD2006-00023 from the Spanish Ministry of Science and Innovation and grants BFU2012-37163 and BFU2015-68726-P from the Spanish Ministry of Economy and Competitiveness. The CRG acknowledges support of the Spanish Ministry of Science and Innovation to the EMBL partnership, the Centro de Excelencia Severo Ochoa, and the CERCA Programme/Generalitat de Catalunya. CIBER Cardiovascular (Fondo de Investigación Sanitaria del Instituto de Salud Carlos III and co-funding by Fondo Europeo de Desarrollo Regional FEDER). The Centro Nacional de Investigaciones Cardiovasculares (CNIC) is supported by the Spanish Ministry of Economy and Competitiveness (MINECO) and the Pro-CNIC Foundation and is a Severo Ochoa Center of Excellence (MINECO award SEV-2015- 0505). The Centro Nacional de Biotecnología (CNB) is a Severo Ochoa Center of Excellence (MINECO award SEV 2017-0712). Funding agencies have not intervened in the design of the studies, with no copyright over the stud

Tpx2, a Novel Xenopus Map Involved in Spindle Pole Organization

TPX2, the targeting protein for Xenopus kinesin-like protein 2 (Xklp2), was identified as a microtubule-associated protein that mediates the binding of the COOH-terminal domain of Xklp2 to microtubules (Wittmann, T., H. Boleti, C. Antony, E. Karsenti, and I. Vernos. 1998. J. Cell Biol. 143:673–685). Here, we report the cloning and functional characterization of Xenopus TPX2. TPX2 is a novel, basic 82.4-kD protein that is phosphorylated during mitosis in a microtubule-dependent way. TPX2 is nuclear during interphase and becomes localized to spindle poles in mitosis. Spindle pole localization of TPX2 requires the activity of the dynein–dynactin complex. In late anaphase TPX2 becomes relocalized from the spindle poles to the midbody. TPX2 is highly homologous to a human protein of unknown function and thus defines a new family of vertebrate spindle pole components. We investigated the function of TPX2 using spindle assembly in Xenopus egg extracts. Immunodepletion of TPX2 from mitotic egg extracts resulted in bipolar structures with disintegrating poles and a decreased microtubule density. Addition of an excess of TPX2 to spindle assembly reactions gave rise to monopolar structures with abnormally enlarged poles. We conclude that, in addition to its function in targeting Xklp2 to microtubule minus ends during mitosis, TPX2 also participates in the organization of spindle poles