Ventx factors function as Nanog-like guardians of developmental potential in Xenopus

International audienceVertebrate development requires progressive commitment of embryonic cells into specific lineages through a continuum of signals that play off differentiation versus multipotency. In mammals, Nanog is a key transcription factor that maintains cellular pluripotency by controlling competence to respond to differentiation cues. Nanog orthologs are known in most vertebrates examined to date, but absent from the Anuran amphibian Xenopus. Interestingly, in silico analyses and literature scanning reveal that basal vertebrate ventral homeobox (ventxs) and mammalian Nanog factors share extensive structural, evolutionary and functional properties. Here, we reassess the role of ventx activity in Xenopus laevis embryos and demonstrate that they play an unanticipated role as guardians of high developmental potential during early development. Joint over-expression of Xenopus ventx1.2 and ventx2.1-b (ventx1/2) counteracts lineage commitment towards both dorsal and ventral fates and prevents msx1-induced ventralization. Furthermore, ventx1/2 inactivation leads to down-regulation of the multipotency marker oct91 and to premature differentiation of blastula cells. Finally, supporting the key role of ventx1/2 in the control of developmental potential during development, mouse Nanog (mNanog) expression specifically rescues embryonic axis formation in ventx1/2 deficient embryos. We conclude that during Xenopus development ventx1/2 activity, reminiscent of that of Nanog in mammalian embryos, controls the switch of early embryonic cells from uncommitted to committed states

Hydrogen bioelectrooxidation on gold nanoparticle-based electrodes modified by Aquifex aeolicus hydrogenase: Application to hydrogen/oxygen enzymatic biofuel cells

International audienceFor the first time, gold nanoparticle-based electrodes have been used as platforms for efficient immobilization of the [NiFe] hydrogenase from the hyperthermophilic bacterium Aquifex aeolicus. AuNPs were characterized by electronic microscopy, dynamic light scattering and UV-Vis spectroscopy. Two sizes around 20.0 ± 5.3 nm and 37.2 ± 4.3 nm nm were synthesized. After thiol-based functionalization, the AuNPs were proved to allow direct H2 oxidn. over a large range of temps. A high c.d. up to 1.85 ± 0.15 mA·cm- 2 was reached at the smallest AuNPs, which is 170 times higher than the one recorded at the bare gold electrode. The catalytic current was esp. studied as a function of the AuNP size and amt., and procedure for deposition. A synergetic effect between the AuNP porous deposit and the increase surface area was shown. Compared to previously used nanomaterials such as carbon nanofibers, the covalent grafting of the enzyme on the thiol-modified gold nanoparticles was shown to enhance the stability of the hydrogenase. This bioanode was finally coupled to a biocathode where BOD from Myrothecium verrucaria was immobilized on AuNP-based film. The performance of the so-mounted H2/O2 biofuel cell was evaluated, and a power d. of 0.25 mW·cm- 2 was recorded. [on SciFinder(R)

The PTK7 and ROR2 Protein Receptors Interact in the Vertebrate WNT/Planar Cell Polarity (PCP) Pathway *

International audienceBackground: The planar cell polarity pathway plays important roles in morphogenetic processes. Results: PTK7 and ROR2 form a heterodimeric complex and bind to WNT5A, promoting JNK phosphorylation and regulating expression of paraxial protocadherin. Conclusion: PTK7 and ROR2 promote cell movement in mammalian cells and coordinate cell polarity during morphogenetic movements. Significance: We reveal new mechanisms of action of PTK7 in WNT/PCP signaling. The non-canonical WNT/planar cell polarity (WNT/PCP) pathway plays important roles in morphogenetic processes in vertebrates. Among WNT/PCP components, protein tyrosine kinase 7 (PTK7) is a tyrosine kinase receptor with poorly defined functions lacking catalytic activity. Here we show that PTK7 associates with receptor tyrosine kinase-like orphan receptor 2 (ROR2) to form a heterodimeric complex in mammalian cells. We demonstrate that PTK7 and ROR2 physically and functionally interact with the non-canonical WNT5A ligand, leading to JNK activation and cell movements. In the Xenopus embryo, Ptk7 functionally interacts with Ror2 to regulate protocadherin papc expression and morphogenesis. Furthermore , we show that Ptk7 is required for papc activation induced by Wnt5a. Interestingly, we find that Wnt5a stimulates the release of the tagged Ptk7 intracellular domain, which can translocate into the nucleus and activate papc expression. This study reveals novel molecular mechanisms of action of PTK7 in non-canonical WNT/PCP signaling that may promote cell and tissue movements

Further Comparison between ATNoSFERES and XCSM

International audienceIn this paper we present ATNoSFERES, a new framework based on an indirect encoding Genetic Algorithm which builds finite-state automata controllers able to deal with perceptual aliazing. In the context of our ongoing line of research, we compare it with XCSM, a memory-based extension of the most studied Learning Classifier System, XCS, through two benchmark experiments. We focus in particular on internal state generalization, and add special purpose features to ATNoSFERES to fulfill that comparison. We then discuss the role played by internal state generalization in the experiments studied

The Enhancer of Trithorax and Polycomb Corto Interacts with Cyclin G in Drosophila

BACKGROUND: Polycomb (PcG) and trithorax (trxG) genes encode proteins involved in the maintenance of gene expression patterns, notably Hox genes, throughout development. PcG proteins are required for long-term gene repression whereas TrxG proteins are positive regulators that counteract PcG action. PcG and TrxG proteins form large complexes that bind chromatin at overlapping sites called Polycomb and Trithorax Response Elements (PRE/TRE). A third class of proteins, so-called "Enhancers of Trithorax and Polycomb" (ETP), interacts with either complexes, behaving sometimes as repressors and sometimes as activators. The role of ETP proteins is largely unknown. METHODOLOGY/PRINCIPAL FINDINGS: In a two-hybrid screen, we identified Cyclin G (CycG) as a partner of the Drosophila ETP Corto. Inactivation of CycG by RNA interference highlights its essential role during development. We show here that Corto and CycG directly interact and bind to each other in embryos and S2 cells. Moreover, CycG is targeted to polytene chromosomes where it co-localizes at multiple sites with Corto and with the PcG factor Polyhomeotic (PH). We observed that corto is involved in maintaining Abd-B repression outside its normal expression domain in embryos. This could be achieved by association between Corto and CycG since both proteins bind the regulatory element iab-7 PRE and the promoter of the Abd-B gene. CONCLUSIONS/SIGNIFICANCE: Our results suggest that CycG could regulate the activity of Corto at chromatin and thus be involved in changing Corto from an Enhancer of TrxG into an Enhancer of PcG

Aggregate Selection in Evolutionary Robotics

Can the processes of natural evolution be mimicked to create robots or autonomous agents? This question embodies the most fundamental goals of evolutionary robotics (ER). ER is a field of research that explores the use of artificial evolution and evolutionary computing for learning of control in autonomous robots, and in autonomous agents in general. In a typical ER experiment, robots, or more precisely their control systems, are evolved to perform a given task in which they must interact dynamically with their environment. Controllers compete in the environment and are selected and propagated based on their ability (or fitness) to perform the desired task. A key component of this process is the manner in which the fitness of the evolving controllers is measured. In ER, fitness is measured by a fitness function or objective function. This function applies some given criteria to determine which robots or agents are better at performing the task for which they are being evolved. Fitness functions can introduce varying levels of a priori knowledge into evolving populations. Som