Actin and spectrin play important roles in neurons, but their organization in axons and dendrites remains unclear. We used stochastic optical reconstruction microscopy (STORM) to study the organization of actin, spectrin and associated proteins in neurons. Actin formed ring-like structures that wrapped around the circumference of axons and evenly spaced along axonal shafts with a periodicity of ~180–190 nm. This periodic structure was not observed in dendrites, which instead contained long actin filaments running along dendritic shafts. Adducin, an actin-capping protein, colocalized with the actin rings. Spectrin exhibited periodic structures alternating with those of actin and adducin, and the distance between adjacent actin-adducin rings was comparable to the length of a spectrin tetramer. Sodium channels in axons were distributed in a periodic pattern coordinated with the underlying actin-spectrin-based cytoskeleton.

Actin, spectrin, and associated molecules form a periodic sub-membrane lattice structure in axons. How this membrane skeleton is developed and why it preferentially forms in axons are unknown. Here, we studied the developmental mechanism of this lattice structure. We found that this structure emerged early during axon development and propagated from proximal regions to distal ends of axons. Components of the axon initial segment were recruited to the lattice late during development. Formation of the lattice was regulated by the local concentration of βII spectrin, which is higher in axons than in dendrites. Increasing the dendritic concentration of βII spectrin by overexpression or by knocking out ankyrin B induced the formation of the periodic structure in dendrites, demonstrating that the spectrin concentration is a key determinant in the preferential development of this structure in axons and that ankyrin B is critical for the polarized distribution of βII spectrin in neurites.DOI: http://dx.doi.org/10.7554/eLife.04581.001

Imaging membranes in live cells with nanometer-scale resolution promises to reveal ultrastructural dynamics of organelles that are essential for cellular functions. In this work, we identified photoswitchable membrane probes and obtained super-resolution fluorescence images of cellular membranes. We demonstrated the photoswitching capabilities of eight commonly used membrane probes, each specific to the plasma membrane, mitochondria, the endoplasmic recticulum (ER) or lysosomes. These small-molecule probes readily label live cells with high probe densities. Using these probes, we achieved dynamic imaging of specific membrane structures in living cells with 30-60 nm spatial resolution at temporal resolutions down to 1-2 s. Moreover, by using spectrally distinguishable probes, we obtained two-color super-resolution images of mitochondria and the ER. We observed previously obscured details of morphological dynamics of mitochondrial fusion/fission and ER remodeling, as well as heterogeneous membrane diffusivity on neuronal processes.nanoscopy | diffraction limit | photoswitchable dye | stochastic optical reconstruction microscopy | photoactivation localization microscopy

No abstract

Key points• The organization of the spinal circuitry responsible for the generation of locomotor rhythm and control of locomotion in mammals is largely unknown, though several types of spinal interneurons involved in the rodent locomotor network have been identified. • Ventral root recordings of spinal motoneurons during fictive locomotion in the isolated mouse spinal cord show spontaneous deletions of activity. The majority of deletions in the isolated neonatal mouse spinal cord are non-resetting: they do not change the phase of subsequent motor cycles. Flexor and extensor motoneurons express asymmetric responses during deletions: flexor deletions are accompanied by tonic ipsilateral extensor activity, while extensor deletions do not perturb rhythmic ipsilateral flexor activity. Non-resetting deletions on one side of the cord do not perturb rhythmic activity on the other side of the cord and can occur in isolated hemicords.• We have characterized the activity of motoneurons and identified interneurons during spontaneous motor deletions. The motoneurons and a subset of V2a interneurons fall silent during non-resetting motor deletions while a second subset of V2a interneurons and commissural interneurons continue unperturbed rhythmic firing. This allowed us to suggest their involvement at different levels of the locomotor network operation.• We have developed a computational model of the central pattern generator that reproduces, and proposes a mechanistic explanation for, our experimental results. The model provides novel insights into the organization of spinal locomotor networks.Abstract We explored the organization of the spinal central pattern generator (CPG) for locomotion by analysing the activity of spinal interneurons and motoneurons during spontaneous deletions occurring during fictive locomotion in the isolated neonatal mouse spinal cord, following earlier work on locomotor deletions in the cat. In the isolated mouse spinal cord, most spontaneous deletions were non-resetting, with rhythmic activity resuming after an integer number of cycles. Flexor and extensor deletions showed marked asymmetry: flexor deletions were accompanied by sustained ipsilateral extensor activity, whereas rhythmic flexor bursting was not perturbed during extensor deletions. Rhythmic activity on one side of the cord was not perturbed during non-resetting spontaneous deletions on the other side, and these deletions could occur with no input from the other side of the cord. These results suggest that the locomotor CPG has a two-level organization with rhythm-generating (RG) and pattern-forming (PF) networks, in which only the flexor RG network is intrinsically rhythmic. To further explore the neuronal organization of the CPG, we monitored activity of motoneurons and selected identified

Highlights d Peripheral CD4 + T cells control stress-induced anxiety-like behavior d Mitochondrial fission in peripheral CD4 + T cell causes severe anxiety symptoms d T cell-derived xanthine acts on the oligodendrocytes in the left amygdala d IRF-1 controls purine synthesis in CD4 + T cells and triggers the onset of anxiety

No abstract

Interactions between ankyrin-B and both dynactin and phosphatidylinositol 3-phosphate lipids promote fast axonal transport of organelles.