Dynamic changes in endoplasmic reticulum morphology and its contact with the plasma membrane in motor neurons in response to nerve injury.

The endoplasmic reticulum (ER) extends throughout a cell and plays a critical role in maintaining cellular homeostasis. Changes in ER shape could provide a clue to explore the mechanisms that underlie the fate determination of neurons after axon injury because the ER drastically changes its morphology under neuronal stress to maintain cellular homeostasis and recover from damage. Because of their tiny structures and richness in the soma, the detailed morphology of the ER and its dynamics have not been well analysed.

Three-dimensional ultrastructure analysis of organelles in injured motor neuron.

Morphological analysis of organelles is one of the important clues for understanding the cellular conditions and mechanisms occurring in cells. In particular, nanoscale information within crowded intracellular organelles of tissues provide more direct implications when compared to analyses of cells in culture or isolation. However, there are some difficulties in detecting individual shape using light microscopy, including super-resolution microscopy.

Axonal injury alters the extracellular glial environment of the axon initial segment and allows substantial mitochondrial influx into axon initial segment.

The axon initial segment (AIS) is structurally and functionally distinct from other regions of the axon, yet alterations in the milieu of the AIS after brain injury have not been well characterized. In this study, we have examined extracellular and intracellular changes in the AIS after hypoglossal nerve injury. Microglial adhesions to the AIS were rarely observed in healthy controls, whereas microglial adhesions to the AIS became apparent in the axonal injury model.

Morphology, localization, and postnatal development of dural macrophages.

The dura mater contains abundant macrophages whose functions remain largely elusive. Recent studies have demonstrated the origin, as well as the gene expression pattern, of dural macrophages (dMΦs). However, their histological features have not been explored yet.

Ultrastructural comparison of dendritic spine morphology preserved with cryo and chemical fixation.

Previously, we showed that cryo fixation of adult mouse brain tissue gave a truer representation of brain ultrastructure in comparison with a standard chemical fixation method (Korogod et al., 2015). Extracellular space matched physiological measurements, there were larger numbers of docked vesicles and less glial coverage of synapses and blood capillaries.

Astrocytic phagocytosis is a compensatory mechanism for microglial dysfunction.

Microglia are the principal phagocytes that clear cell debris in the central nervous system (CNS). This raises the question, which cells remove cell debris when microglial phagocytic activity is impaired. We addressed this question using Siglech mice, which enable highly specific ablation of microglia.

Three-dimensional analysis of somatic mitochondrial dynamics in fission-deficient injured motor neurons using FIB/SEM.

Mitochondria undergo morphological changes through fusion and fission for their quality control, which are vital for neuronal function. In this study, we examined three-dimensional morphologies of mitochondria in motor neurons under normal, nerve injured, and nerve injured plus fission-impaired conditions using the focused ion beam/scanning electron microscopy (FIB/SEM), because the FIB/SEM technology is a powerful tool to demonstrate both 3D images of whole organelle and the intra-organellar structure simultaneously. Crossing of dynamin-related protein 1 (Drp1) gene-floxed mice with neuronal injury-specific Cre driver mice, Atf3:BAC Tg mice, allowed for Drp1 ablation specifically in injured neurons.

Mitochondria-associated membrane collapse is a common pathomechanism in SIGMAR1- and SOD1-linked ALS.

A homozygous mutation in the gene for sigma 1 receptor (Sig1R) is a cause of inherited juvenile amyotrophic lateral sclerosis (ALS16). Sig1R localizes to the mitochondria-associated membrane (MAM), which is an interface of mitochondria and endoplasmic reticulum. However, the role of the MAM in ALS is not fully elucidated.

Suppression of c-Kit signaling induces adult neurogenesis in the mouse intestine after myenteric plexus ablation with benzalkonium chloride.

Adult neurogenesis rarely occurs in the enteric nervous system (ENS). In this study, we demonstrated that, after intestinal myenteric plexus (MP) ablation with benzalkonium chloride (BAC), adult neurogenesis in the ENS was significantly induced in c-kit loss-of-function mutant mice (W/W(v)). Almost all neurons and fibers in the MP disappeared after BAC treatment.

Mitochondrial fission is an acute and adaptive response in injured motor neurons.

Successful recovery from neuronal damage requires a huge energy supply, which is provided by mitochondria. However, the physiological relevance of mitochondrial dynamics in damaged neurons in vivo is poorly understood. To address this issue, we established unique bacterial artificial chromosome transgenic (BAC Tg) mice, which develop and function normally, but in which neuronal injury induces labelling of mitochondria with green fluorescent protein (GFP) and expression of cre recombinase.

ECEL1 mutation implicates impaired axonal arborization of motor nerves in the pathogenesis of distal arthrogryposis.

The membrane-bound metalloprotease endothelin-converting enzyme-like 1 (ECEL1) has been newly identified as a causal gene of a specific type of distal arthrogryposis (DA). In contrast to most causal genes of DA, ECEL1 is predominantly expressed in neuronal cells, suggesting a unique neurogenic pathogenesis in a subset of DA patients with ECEL1 mutation. The present study analyzed developmental motor innervation and neuromuscular junction formation in limbs of the rodent homologue damage-induced neuronal endopeptidase (DINE)-deficient mouse.

Existence of c-Kit negative cells with ultrastructural features of interstitial cells of Cajal in the subserosal layer of the W/W(v) mutant mouse colon.

Interstitial cells of Cajal (ICC) are mesenchymal cells that are distributed along the gastrointestinal tract and function as pacemaker cells or intermediary cells between nerves and smooth muscle cells. ICC express a receptor tyrosine kinase c-Kit, which is an established marker for ICC. The c-kit gene is allelic with the murine white-spotting locus (W), and some ICC subsets were reported to be missing in heterozygous mutant W/W(v) mice carrying W and W(v) mutated alleles.

Ultrastructural characterization of interstitial cells of Cajal associated with the submucosal plexus in the proximal colon of the guinea pig.

Interstitial cells of Cajal (ICC) associated with the submucosal (submucous) plexus (ICC-SP) in the proximal colon of the guinea pig were studied by immunohistochemistry and electron microscopy. Whole-mount stretch preparations with c-Kit immunohistochemistry revealed that a number of ICC-SP constituted a dense cellular network around the submucosal plexus. Some of these ICC-SP were observed in the vicinity of the muscularis mucosae in sections immunostained for c-Kit and α-smooth muscle actin.

Three-dimensional demonstration of the interstitial cells of Cajal associated with the submucosal plexus in guinea-pig caecum.

The guinea-pig caecum was studied by using immunohistochemistry for Kit receptors and nerves to clarify whether interstitial cells of Cajal (ICC) were localized in association with the submucosal plexus (ICC-SP). A large area of the guinea-pig caecum was nearly devoid of longitudinal muscles, because they were concentrated into three bundles of the taenia caeci (coli) and this allowed clear observation of the myenteric and submucosal plexus as separate networks in whole-mount stretch preparations. The myenteric plexus was observed as a loose polygonal network consisting in elongated ganglia and long connecting nerve strands, whereas the submucosal plexus was identified as smaller ovoid ganglia connected to much thinner nerve strands in different tissue layers.