In vivo assembly of the axon initial segment in motor neurons

International audienceThe axon initial segment (AIS) is responsible for both the modulation of action potentials and the maintenance of neuronal polarity. Yet, the molecular mechanisms controlling its assembly are incompletely understood. Our study in single electroporated motor neurons in mouse embryos revealed that AnkyrinG (AnkG), the AIS master organizer, is undetectable in bipolar migrating motor neurons, but is already expressed at the beginning of axonogenesis at E9.5 and initially distributed homogeneously along the entire growing axon. Then, from E11.5, a stage when AnkG is already apposed to the membrane, as observed by electron microscopy, the protein progressively becomes restricted to the proximal axon. Analysis on the global motor neurons population indicated that Neurofascin follows an identical spatio-temporal distribution, whereas sodium channels and beta 4-spectrin only appear along AnkG(+) segments at E11.5. Early patch-clamp recordings of individual motor neurons indicated that at E12.5 these nascent AISs are already able to generate spikes. Using knock-out mice, we demonstrated that neither beta 4-spectrin nor Neurofascin control the distal-to-proximal restriction of AnkG

The branching gene RAMOSUS1 mediates interactions among two novel signals and auxin in pea

In Pisum sativium, the RAMOSUS genes RMS1, RMS2, and RMS5 regulate shoot branching via physiologically defined mobile signals. RMS1 is most likely a carotenoid cleavage enzyme and acts with RMS5 to control levels of an as yet unidentified mobile branching inhibitor required for auxin inhibition of branching. Our work provides molecular, genetic, and physiological evidence that RMS1 plays a central role in a shoot-to-root-to-shoot feedback system that regulates shoot branching in pea. Indole-3-acetic acid (IAA) positively regulates RMS1 transcript level, a potentially important mechanism for regulation of shoot branching by IAA. In addition, RMS1 transcript levels are dramatically elevated in rms3, rms4, and rms5 plants, which do not contain elevated IAA levels. This degree of upregulation of RMS1 expression cannot be achieved in wild-type plants by exogenous IAA application. Grafting studies indicate that an IAA-independent mobile feedback signal contributes to the elevated RMS1 transcript levels in rms4 plants. Therefore, the long-distance signaling network controlling branching in pea involves IAA, the RMS1 inhibitor, and an IAA-independent feedback signal. Consistent with physiological studies that predict an interaction between RMS2 and RMS1, rms2 mutations appear to disrupt this IAA-independent regulation of RMS1 expression

Synthesis and characterization of carboxylic-and amine-grafted FAU zeolites as inorganic fillers to design biocompatible composites

Highlights:-Surface functionalization of FAU via APTES or TESPA allowed to graft either amine or carboxylate groups, to mediate their covalent incorporation into a gelatin hydrogel.-Thermal properties of the resulting composites were substantially improved compared with non-crosslinked conditions.-The FAU/gelatin composites were found biocompatible with respect to macrophagederived THP-1 cells

SWITCH1 (SWI1): a novel protein required for the establishment of sister chromatid cohesion and for bivalent formation at meiosis

We have characterized a new gene, SWI1, involved in sister chromatid cohesion during both male and female meiosis in Arabidopsis thaliana. A first allele, swi1.1, was obtained as a T-DNA tagged mutant and was described previously as abnormal exclusively in female meiosis. We have isolated a new allele, swi1.2, which is defective for both male and female meiosis. In swi1.2 male meiosis, the classical steps of prophase were not observed, especially because homologs do not synapse. Chromatid arms and centromeres lost their cohesion in a stepwise manner before metaphase I, and 20 chromatids instead of five bivalents were seen at the metaphase plate, which was followed by an aberrant segregation. In contrast, swi1.2 female meiocytes performed a mitotic-like division instead of meiosis, indicating a distinct role for SWI1 or a different effect of the loss of SWI1 function in both processes. The SWI1 gene was cloned; the putative SWI1 protein did not show strong similarity to any known protein. Plants transformed with a SWI1–GFP fusion indicated that SWI1 protein is present in meiocyte nuclei, before meiosis and at a very early stage of prophase. Thus, SWI1 appears to be a novel protein involved in chromatid cohesion establishment and in chromosome structure during meiosis, but with clear differences between male and female meiosis

Cooperative Interactions between 480 kDa Ankyrin-G and EB Proteins Assemble the Axon Initial Segment

International audienceThe axon initial segment (AIS) is required for generating action potentials and maintaining neuronal polarity. Significant progress has been made in deciphering the basic building blocks composing the AIS, but the underlying mechanisms required for AIS formation remains unclear. The scaffolding protein ankyrin-G is the master-organizer of the AIS. Microtubules and their interactors, particularly end-binding proteins (EBs), have emerged as potential key players in AIS formation. Here, we show that the longest isoform of ankyrin-G (480AnkG) selectively associates with EBs via its specific tail domain and that this interaction is crucial for AIS formation and neuronal polarity in cultured rodent hippocampal neurons. EBs are essential for 480AnkG localization and stabilization at the AIS, whereas 480AnkG is required for the specific accumulation of EBs in the proximal axon. Our findings thus provide a conceptual framework for understanding how the cooperative relationship between 480AnkG and EBs induces the assembly of microtubule-AIS structures in the proximal axon

Acetylcholine Controls GABA-, Glutamate-, and Glycine-Dependent Giant Depolarizing Potentials that Govern Spontaneous Motoneuron Activity at the Onset of Synaptogenesis in the Mouse Embryonic Spinal Cord

International audienceA remarkable feature of early neuronal networks is their endogenous ability to generate spontaneous rhythmic electrical activity independently of any external stimuli. In the mouse embryonic SC, this activity starts at an embryonic age of similar to 12 d and is characterized by bursts of action potentials recurring every 2-3 min. Although these bursts have been extensively studied using extracellular recordings and are known to play an important role in motoneuron (MN) maturation, the mechanisms driving MN activity at the onset of synaptogenesis are still poorly understood. Because only cholinergic antagonists are known to abolish early spontaneous activity, it has long been assumed that spinal cord (SC) activity relies on a core network of MNs synchronized via direct cholinergic collaterals. Using a combination of whole-cell patch-clamp recordings and extracellular recordings in E12.5 isolated mouse SC preparations, we found that spontaneous MN activity is driven by recurrent giant depolarizing potentials. Our analysis reveals that these giant depolarizing potentials are mediated by the activation of GABA, glutamate, and glycine receptors. We did not detect direct nAChR activation evoked by ACh application on MNs, indicating that cholinergic inputs between MNs are not functional at this age. However, we obtained evidence that the cholinergic dependency of early SC activity reflects a presynaptic facilitation of GABA and glutamate synaptic release via nicotinic AChRs. Our study demonstrates that, even in its earliest form, the activity of spinal MNs relies on a refined poly-synaptic network and involves a tight presynaptic cholinergic regulation of both GABAergic and glutamatergic inputs