Ataxia with giant axonopathy in Acbd5-deficient mice halted by adeno-associated virus gene therapy.

Acyl-CoA binding domain containing 5 (ACBD5) is a critical player in handling very long chain fatty acids (VLCFA) en route for peroxisomal ß-oxidation. Mutations in ACBD5 lead to the accumulation of VLCFA and patients present retinal dystrophy, ataxia, psychomotor delay and a severe leukodystrophy. Using CRISPR/Cas9, we generated and characterized an Acbd5 Gly357* mutant allele. Gly357* mutant mice recapitulated key features of the human disorder, including reduced survival, impaired locomotion and reflexes, loss of photoreceptors, and demyelination. The ataxic presentation of Gly357* mice involved the loss of cerebellar Purkinje cells and a giant axonopathy throughout the CNS. Lipidomic studies provided evidence for the extensive lipid dysregulation caused by VLCFA accumulation. Following a proteomic survey, functional studies in neurons treated with VLCFA unravelled a deregulated cytoskeleton with reduced actin dynamics and increased neuronal filopodia. We also show that an adeno-associated virus-mediated gene delivery ameliorated the gait phenotypes and the giant axonopathy, also improving myelination and astrocyte reactivity. Collectively, we established a mouse model with significance for VLCFA-related disorders. The development of relevant neuropathological outcomes enabled the understanding of mechanisms modulated by VLCFA and the evaluation of the efficacy of preclinical therapeutic interventions.

Potential Role of Fenestrated Septa in Axonal Transport of Golgi Cisternae and Gap Junction Formation/Function.

Crayfish axons contain a system of parallel membranous cisternae spaced by ~2 µm and oriented perpendicularly to the axon's long axis. Each cisterna is composed of two roughly parallel membranes, separated by a 150-400 Å wide space. The cisternae are interrupted by 500-600 Å pores, each occupied by a microtubule. Significantly, filaments, likely made of kinesin, often bridge the gap between the microtubule and the edge of the pore. Neighboring cisternae are linked by longitudinal membranous tubules. In small axons, the cisternae seem to be continuous across the axon, while in large axons they are intact only at the axon's periphery. Due to the presence of pores, we have named these structures "Fenestrated Septa" (FS). Similar structures are also present in vertebrates, including mammals, proving that they are widely expressed in the animal kingdom. We propose that FS are components of the "anterograde transport" mechanism that moves cisternae of the Golgi apparatus (GA) toward the nerve ending by means of motor proteins, likely to be kinesins. In crayfish lateral giant axons, we believe that vesicles that bud off FS at the nerve ending contain gap junction hemichannels (innexons) for gap junction channel and hemichannel formation and function.

Phylogenetics of swimming behaviour in Medusozoa: the role of giant axons and their possible evolutionary origin.

Although neural tissues in cnidarian hydroids have a nerve net structure, some cnidarian medusae contain well-defined nerve tracts. As an example, the hydrozoan medusa Aglantha digitale has neural feeding circuits that show an alignment and condensation, which is absent in its relatives Aequorea victoria and Clytia hemisphaerica. In some cases, neural condensations take the form of fast propagating giant axons concerned with escape or evasion. Such giant axons appear to have developed from the fusion of many, much finer units. Ribosomal DNA analysis has identified the lineage leading to giant axon-based escape swimming in Aglantha and other members of the Aglaura clade of trachymedusan jellyfish. The Aglaura, along with sister subclades that include species such as Colobonema sericeum, have the distinctive ability to perform dual swimming, i.e. to swim at either high or low speeds. However, the form of dual swimming exhibited by Colobonema differs both biomechanically and physiologically from that in Aglantha and is not giant axon based. Comparisons between the genomes of such closely related species might provide a means to determine the molecular basis of giant axon formation and other neural condensations. The molecular mechanism responsible may involve 'fusogens', small molecules possibly derived from viruses, which draw membranes together prior to fusion. Identifying these fusogen-based mechanisms using genome analysis may be hindered by the many changes in anatomy and physiology that followed giant axon evolution, but the genomic signal-to-noise ratio may be improved by examining the convergent evolution of giant axons in other hydrozoa, such as the subclass Siphonophora.

"You've Got to Work on This Axon": J. Z. Young and Squid Giant Axon Preparations in 20th -Century Neurobiology.

Employing and extending Hans-Jörg Rheinberger's analytical concept of epistemic things, this essay proposes one reason why squid giant axons, unusually large invertebrate nerve fibers, had such great impacts on twentieth-century neurobiology. The 1930s characterizations of these axons by John Zachary Young reshaped prevailing assumptions about nerve cells as epistemic things, I argue. Specifically, Young's preparations of these axons, which consisted of fibers attached to laboratory technologies, highlighted similarities between giant axons and more familiar ones via lines of comparative study common to aquatic biology. Young's work convinced other biologists that the squid giant fibers were, in fact, axons, despite their unusual fused (syncytial) structures, thereby promoting further studies, such as intracellular measurements, made possible by the fiber's size. Tracing direct relations between preparations of squid axons and broader interpretations of neurons as epistemic things, this paper renders an actors' category, "preparations," into an analytical one. In turn, it offers glimpses into how aquatic organisms shaped twentieth-century neurobiology and how local experiments can drive broader, disciplinary changes.

Connexin/Innexin Channels in Cytoplasmic Organelles. Are There Intracellular Gap Junctions? A Hypothesis!

This paper proposes the hypothesis that cytoplasmic organelles directly interact with each other and with gap junctions forming intracellular junctions. This hypothesis originated over four decades ago based on the observation that vesicles lining gap junctions of crayfish giant axons contain electron-opaque particles, similar in size to junctional innexons that often appear to directly interact with junctional innexons; similar particles were seen also in the outer membrane of crayfish mitochondria. Indeed, vertebrate connexins assembled into hexameric connexons are present not only in the membranes of the Golgi apparatus but also in those of the mitochondria and endoplasmic reticulum. It seems possible, therefore, that cytoplasmic organelles may be able to exchange small molecules with each other as well as with organelles of coupled cells via gap junctions.

Giant Axonal Neuropathy: A Case Report of Subclinical Childhood Manifestations.

Giant axonal neuropathy (GAN) is a rare, inherited neurodegenerative disease that affects both the central and peripheral nervous systems. It is mostly characterized by a progressive loss of motor and sensory function, which can begin in early childhood. GAN is thought to be caused by a mutation in the GAN gene on chromosome 16q24.1. We report a seven-year-old Saudi male child with GAN who was diagnosed using whole-exome sequencing. The child presented with a history of progressive weakness and muscle wasting in the arms and legs as well as difficulty walking. The sequencing identified a mutation in the GAN gene (NM_022041.3: c.1456G>A). Electrodiagnostic studies showed evidence of diffuse axonal motor and sensory polyneuropathy involving cranial nerves. This case report adds to the growing evidence that whole-exome sequencing can be a useful tool for diagnosing rare inherited neuromuscular disorders. It also highlights the importance of early diagnosis and intervention for this condition.

The brain structure of selected trypanorhynch tapeworms.

The brain architecture in four species of tapeworms from the order Trypanorhyncha has been studied. In all species, the brain consists of paired anterior and lateral lobes, and an unpaired central lobe. The anterior lobes connect by dorsal and ventral semicircular commissures; the central and lateral lobes connect by a median and an X-shaped crisscross commissure. In the center of the brain, five well-developed compact neuropils are present. The brain occupies a medial position in the scolex pars bothrialis. The ventral excretory vessels are situated outside the lateral lobes of the brain; the dorsal excretory vessels are located inside the brain and dorsal to the median commissure. The brain gives rize four anterior proboscis nerves and four posterior bulbar nerves with myelinated giant axons (GAs). The cell bodies of the GAs are located within the X-commissure and in the bulbar nerves. Highly developed serotonergic neuropils are present in the anterior and lateral lobes; numerous 5-HT neurons are found in the brain lobes including the central unpaired lobe. The X-cross commissure consists of the α-tub-immunoreactive and 5-HT-IR neurites. Eight ultrastructural types of neurons were found in the brain of the three species investigated. In addition, different types of synapses were present in the neuropils. Glial cells ensheath the brain lobes, the neuropils, the GAs, and the bulbar nerves. Glia cell processes form complex branching patterns of thin cytoplasmic sheets sandwiched between adjacent neural processes and filling the space between neurons. Multilayer myelin-like envelopes and a mesaxon-like structure have been found in Trypanorhyncha nervous system. We compared the brain architecture of Trypanorhyncha with that of an early basal cestode taxon, that is, Diphyllobothriidea, and present a hypothesis about the homology of the anterior brain lobes in order Trypanorhyncha; and the lateral lobes and median commissure are homologous brain structures within Eucestoda.

Mechanical properties of the lamprey spinal cord: uniaxial loading and physiological strain.

During spinal cord injury, nerves suffer a strain beyond their physiological limits which damages and disrupts their structure. Research has been done to measure the modulus of the spinal cord and surrounding tissue; however the relationship between strain and spinal cord fibers is still unclear. In this work, our objective is to measure the stress-strain response of the spinal cord in vivo and in vitro and model this response as a function of the number of fibers. We used the larvae lamprey (Petromyzon Marinus), a model for spinal cord regeneration and animal locomotion. We found that physiologically the spinal cord is pre-stressed to a longitudinal strain of 10% and this strain increases to 15% during swimming. Tensile measurements show that uniaxial, longitudinal loading is independent of the meninges. Stress values for uniaxial strains below 18%, are homogeneous through the length of the body. However, for higher uniaxial strains the Head section shows more resistance to longitudinal loading than the Tail. These data, together with the number of fibers obtained from histological sections were used in a composite-material model to obtain the properties of the spinal cord fibers (2.4 MPa) and matrix (0.017 MPa) to uniaxial longitudinal loading. This model allowed us to approximate the percentage of fibers in the spinal cord, establishing a relationship between uniaxial longitudinal strains and spinal cord composition. We showed that there is a proportional relationship between the number of fibers and the properties of the spinal cord at large uniaxial strains.

Giant axonal neuropathy.

Giant axonal neuropathy (GAN) is a rare hereditary autosomal recessive neurodegenerative disease affecting both the peripheral and the central nervous system. Clinically it is characterized by an age of onset during the first decade, progressive and severe motor sensory neuropathy followed, in some patients, by the occurrence of various central nervous system signs such as cerebellar syndrome, upper motor neuron signs, or epilepsy. Although kinky hairs are reported in the majority of patients, it is not a constant finding. The prognosis is usually severe with death occurring during the second or third decade; nevertheless a less severe course is reported in some patients. The presence of a variable number of giant axons filled with neurofilaments in the nerve biopsy represents the pathological feature of the disease and it is usually associated to a variable degree with axonal loss and demyelization. Giant axons are also found in the central nervous system associated with Rosenthal fibers and a variable degree of involvement of white matter and neuronal loss. The disease is caused by mutation in the GAN gene encoding for gigaxonin, a member of BTB-Kelch. Up to now 37 mutations in the GAN gene have been reported. These mutations are scattered over the 11 exons of the gene without a clear genotype-phenotype correlation. These mutations resulting in gigaxonin deficiency lead to a slow down in ubiquitin-mediated protein degradation and possibly of other unidentified proteins. GAN represents a good model of a neurodegenerative disorder in which there is a primary defect of the ubiquitin proteasome system and its network with neurofilaments. The clarification of molecular mechanisms involved in GAN can help in understanding other frequent neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and Parkinson disease.