Inactivation of vimentin in satellite glial cells affects dorsal root ganglion intermediate filament expression and neuronal axon growth in vitro.

Peripheral nerve trauma and regeneration are complex events, and little is known concerning how occurrences in the distal stump affect the cell body's response to injury. Intermediate filament (IF) proteins underpin cellular architecture and take part in nerve cell proliferation, differentiation and axon regeneration, but their role in these processes is not yet fully understood. The present study aimed to investigate the regulation and interrelationship of major neural IFs in adult dorsal root ganglion (DRG) neurons and satellite glial cells (SGCs) following sciatic nerve injury. We demonstrated that the expression of neural IFs in DRG neurons and SGCs after axotomy depends on vimentin activity. In intact DRGs, synemin M and peripherin proteins are detected in small neurons while neurofilament L (NFL) and synemin L characterize large neurons. Both neuronal populations are surrounded by vimentin positive- and glial fibrillary acidic protein (GFAP)-negative SGCs. In response to axotomy, synemin M and peripherin were upregulated in large wild-type DRG neurons and, to a lesser extent, in vim-/- and synm-/- DRG neurons, suggesting the role for these IFs in axon regeneration. However, an increase in the number of NFL-positive small neurons was observed in vim-/- mice, accompanied by a decrease of peripherin-positive small neurons. These findings suggest that vimentin is required for injury-induced neuronal IF remodeling. We further show that vimentin is also indispensable for nerve injury-induced GFAP upregulation in perineuronal SGCs and that inactivation of vimentin and synemin appears to accelerate the rate of DRG neurite regeneration at early stages in vitro.

Recovery from tachyphylaxis of TRPV1 coincides with recycling to the surface membrane.

The transient receptor potential vanilloid-1 (TRPV1) ion channel is essential for sensation of thermal and chemical pain. TRPV1 activation is accompanied by Ca2+-dependent desensitization; acute desensitization reflects rapid reduction in channel activity during stimulation, whereas tachyphylaxis denotes the diminution in TRPV1 responses to repetitive stimulation. Acute desensitization has been attributed to conformational changes of the TRPV1 channel; however, the mechanisms underlying the establishment of tachyphylaxis remain to be defined. Here, we report that the degree of whole-cell TRPV1 tachyphylaxis is regulated by the strength of inducing stimulation. Using light-sheet microscopy and pH-sensitive sensor pHluorin to follow TRPV1 endocytosis and exocytosis trafficking, we provide real-time information that tachyphylaxis of different degrees concurs with TRPV1 recycling to the plasma membrane in a proportional manner. This process controls TRPV1 surface expression level thereby the whole-cell nociceptive response. We further show that activity-gated TRPV1 trafficking associates with intracellular Ca2+ signals of distinct kinetics, and recruits recycling routes mediated by synaptotagmin 1 and 7, respectively. These results suggest that activity-dependent TRPV1 recycling contributes to the establishment of tachyphylaxis.

The GSK3-MAP1B pathway controls neurite branching and microtubule dynamics.

The microtubule-associated protein MAP1B plays a key role in axon regeneration. We investigated the role of GSK3-mediated MAP1B phosphorylation in local fine-tuning of neurite branching and the underlying microtubule (MT) dynamics. In wildtype adult dorsal root ganglia (DRG) neurons, MAP1B phosphorylation is locally reduced at branching points, and branching dynamics from growth cones and distal neurite shafts is increased upon GSK3 inhibition. While map1b-/- neurites, that display increased branching, are not affected by GSK3 inhibition, transfection of map1b-/- neurons with full-length map1b-cDNA restores the wildtype branching phenotype, demonstrating that MAP1B is a key effector downstream of GSK3. Experiments in mutant mice lacking tyrosinated MTs indicate a preferential association of phospho-MAP1B with tyrosinated MTs. Interestingly, inhibition of GSK3-mediated MAP1B phosphorylation in map1b-cDNA-transfected fibroblasts protects both tyrosinated and acetylated MTs from nocodazole-induced depolymerization, while detyrosinated MTs are less abundant in the presence of MAP1B. Our data thus provide new insight into the molecular link between GSK3, MAP1B, neurite branching and MT stability regulation. We suggest that, at branching points, MAP1B undergoes a fine regulation of both its phosphorylation and sub-cellular amounts, in order to modulate the local balance between acetylated, detyrosinated, and tyrosinated microtubule pools.

Giant scaffolding protein AHNAK1 interacts with ß-dystroglycan and controls motility and mechanical properties of Schwann cells.

The profound morphofunctional changes that Schwann cells (SCs) undergo during their migration and elongation on axons, as well as during axon sorting, ensheathment, and myelination, require their close interaction with the surrounding laminin-rich basal lamina. In contrast to myelinating central nervous system glia, SCs strongly and constitutively express the giant scaffolding protein AHNAK1, localized essentially underneath the outer, abaxonal plasma membrane. Using electron microscopy, we show here that in the sciatic nerve of ahnak1(-) (/) (-) mice the ultrastructure of myelinated, and unmyelinated (Remak) fibers is affected. The major SC laminin receptor ß-dystroglycan co-immunoprecipitates with AHNAK1 shows reduced expression in ahnak1(-) (/) (-) SCs, and is no longer detectable in Cajal bands on myelinated fibers in ahnak1(-) (/) (-) sciatic nerve. Reduced migration velocity in a scratch wound assay of purified ahnak1(-) (/) (-) primary SCs cultured on a laminin substrate indicated a function of AHNAK1 in SC motility. This was corroborated by atomic force microscopy measurements, which revealed a greater mechanical rigidity of shaft and leading tip of ahnak1(-) (/) (-) SC processes. Internodal lengths of large fibers are decreased in ahnak1(-) (/) (-) sciatic nerve, and longitudinal extension of myelin segments is even more strongly reduced after acute knockdown of AHNAK1 in SCs of developing sciatic nerve. Together, our results suggest that by interfering in the cross-talk between the transmembrane form of the laminin receptor dystroglycan and F-actin, AHNAK1 influences the cytoskeleton organization of SCs, and thus plays a role in the regulation of their morphology and motility and lastly, the myelination process.

Macrophage polarization in vitro and in vivo modified by contact with fragmented chitosan hydrogel.

We have previously shown that implantation of a fragmented chitosan hydrogel suspension (chitosan-FPHS) into a traumatic spinal cord lesion in adult rats led to significant axon regrowth and functional recovery, which was associated to a modulation of inflammation. Using an in vitro culture system, we show here that polarization of bone marrow-derived macrophages is indeed modified by direct contact with chitosan-FPHS. Reducing the degree of acetylation (DA) and raising the concentration of chitosan (Cp, from 1.5% to 3%), favors macrophage polarization toward anti-inflammatory subtypes. These latter also migrate and adhere efficiently on low, but not high DA chitosan-FPHS, both in vitro and in vivo, while inflammatory macrophages rarely invade a chitosan-FPHS implant in vivo, no matter the DA. Our in vitro model setup should prove a valuable tool for screening diverse biomaterial formulations and combinations thereof for their inflammatory potential prior to implantation in vivo.

Ultrafast Doppler imaging and ultrasound localization microscopy reveal the complexity of vascular rearrangement in chronic spinal lesion.

Acute spinal cord injury (SCI) leads to severe damage to the microvascular network. The process of spontaneous repair is accompanied by formation of new blood vessels; their functionality, however, presumably very important for functional recovery, has never been clearly established, as most studies so far used fixed tissues. Here, combining ultrafast Doppler imaging and ultrasound localization microscopy (ULM) on the same animals, we proceeded at a detailed analysis of structural and functional vascular alterations associated with the establishment of chronic SCI, both at macroscopic and microscopic scales. Using a standardized animal model of SCI, our results demonstrate striking hemodynamic alterations in several subparts of the spinal cord: a reduced blood velocity in the lesion site, and an asymmetrical hypoperfusion caudal but not rostral to the lesion. In addition, the worsening of many evaluated parameters at later time points suggests that the neoformed vascular network is not yet fully operational, and reveals ULM as an efficient in vivo readout for spinal cord vascular alterations. Finally, we show statistical correlations between the diverse biomarkers of vascular dysfunction and SCI severity. The imaging modality developed here will allow evaluating recovery of vascular function over time in pre-clinical models of SCI. Also, used on SCI patients in combination with other quantitative markers of neural tissue damage, it may help classifying lesion severity and predict possible treatment outcomes in patients.

Distinct roles of c-Jun N-terminal kinase isoforms in neurite initiation and elongation during axonal regeneration.

c-Jun N-terminal kinases (JNKs) (comprising JNK1-3 isoforms) are members of the MAPK (mitogen-activated protein kinase) family, activated in response to various stimuli including growth factors and inflammatory cytokines. Their activation is facilitated by scaffold proteins, notably JNK-interacting protein-1 (JIP1). Originally considered to be mediators of neuronal degeneration in response to stress and injury, recent studies support a role of JNKs in early stages of neurite outgrowth, including adult axonal regeneration. However, the function of individual JNK isoforms, and their potential effector molecules, remained unknown. Here, we analyzed the role of JNK signaling during axonal regeneration from adult mouse dorsal root ganglion (DRG) neurons, combining pharmacological JNK inhibition and mice deficient for each JNK isoform and for JIP1. We demonstrate that neuritogenesis is delayed by lack of JNK2 and JNK3, but not JNK1. JNK signaling is further required for sustained neurite elongation, as pharmacological JNK inhibition resulted in massive neurite retraction. This function relies on JNK1 and JNK2. Neurite regeneration of jip1(-/-) DRG neurons is affected at both initiation and extension stages. Interestingly, activated JNKs (phospho-JNKs), as well as JIP1, are also present in the cytoplasm of sprouting or regenerating axons, suggesting a local action on cytoskeleton proteins. Indeed, we have shown that JNK1 and JNK2 regulate the phosphorylation state of microtubule-associated protein MAP1B, whose role in axonal regeneration was previously characterized. Moreover, lack of MAP1B prevents neurite retraction induced by JNK inhibition. Thus, signaling by individual JNKs is differentially implicated in the reorganization of the cytoskeleton, and neurite regeneration.

AAV2/9-mediated silencing of PMP22 prevents the development of pathological features in a rat model of Charcot-Marie-Tooth disease 1 A.

Charcot-Marie-Tooth disease 1 A (CMT1A) results from a duplication of the PMP22 gene in Schwann cells and a deficit of myelination in peripheral nerves. Patients with CMT1A have reduced nerve conduction velocity, muscle wasting, hand and foot deformations and foot drop walking. Here, we evaluate the safety and efficacy of recombinant adeno-associated viral vector serotype 9 (AAV2/9) expressing GFP and shRNAs targeting Pmp22 mRNA in animal models of Charcot-Marie-Tooth disease 1 A. Intra-nerve delivery of AAV2/9 in the sciatic nerve allowed widespread transgene expression in resident myelinating Schwann cells in mice, rats and non-human primates. A bilateral treatment restore expression levels of PMP22 comparable to wild-type conditions, resulting in increased myelination and prevention of motor and sensory impairments over a twelve-months period in a rat model of CMT1A. We observed limited off-target transduction and immune response using the intra-nerve delivery route. A combination of previously characterized human skin biomarkers is able to discriminate between treated and untreated animals, indicating their potential use as part of outcome measures.

Microglia control the glycinergic but not the GABAergic synapses via prostaglandin E2 in the spinal cord.

Microglia control excitatory synapses, but their role in inhibitory neurotransmission has been less well characterized. Herein, we show that microglia control the strength of glycinergic but not GABAergic synapses via modulation of the diffusion dynamics and synaptic trapping of glycine (GlyR) but not GABAA receptors. We further demonstrate that microglia regulate the activity-dependent plasticity of glycinergic synapses by tuning the GlyR diffusion trap. This microglia-synapse cross talk requires production of prostaglandin E2 by microglia, leading to the activation of neuronal EP2 receptors and cyclic adenosine monophosphate-dependent protein kinase. Thus, we now provide a link between microglial activation and synaptic dysfunctions, which are common early features of many brain diseases.

Physical chitosan microhydrogels as scaffolds for spinal cord injury restoration and axon regeneration.

Recovery from traumatic spinal cord injury (SCI) usually fails due to a cascade of cellular and molecular events that compromise neural tissue reconstitution by giving rise to glial scarring and cavity formation. We designed a scaffold material for SCI treatment containing only chitosan and water as fragmented physical hydrogel suspension (Chitosan-FPHS), with defined degree of acetylation (DA), polymer concentration, and mean fragment size. Implantation of Chitosan-FPHS alone into rat spinal cord immediately after a bilateral dorsal hemisection promoted reconstitution of spinal tissue and vasculature, and diminished fibrous glial scarring: with astrocyte processes primarily oriented towards the lesion, the border between lesion site and intact tissue became permissive for regrowth of numerous axons into, and for some even beyond the lesion site. Growing axons were myelinated or ensheathed by endogenous Schwann cells that migrated into the lesion site and whose survival was prolonged. Interestingly, Chitosan-FPHS also modulated the inflammatory response, and we suggest that this might contribute to tissue repair. Finally, this structural remodeling was associated with significant, long-lasting gain in locomotor function recovery. Because it effectively induces neural tissue repair, Chitosan-FPHS biomaterial may be a promising new approach to treat SCI, and a suitable substrate to combine with other strategies.

Microtubule-associated protein 1B controls directionality of growth cone migration and axonal branching in regeneration of adult dorsal root ganglia neurons.

During development, microtubule-associated protein 1B (MAP1B) is one of the earliest MAPs, preferentially localized in axons and growth cones, and plays a role in axonal outgrowth. Although generally downregulated in the adult, we have shown that MAP1B is constitutively highly expressed in adult dorsal root ganglia (DRGs) and associated with central sprouting and peripheral regeneration of these neurons. Mutant mice with a complete MAP1B null allele that survive until adulthood exhibit a reduced myelin sheath diameter and conductance velocity of peripheral axons and lack of the corpus callosum. Here, to determine the function of MAP1B in axonal regeneration, we used cultures of adult DRG explants and/or dissociated neurons derived from this map1b-/- mouse line. Whereas the overall length of regenerating neurites lacking MAP1B was similar to wild-type controls, our analysis revealed two main defects. First, map1b-/- neurites exhibited significantly (twofold) higher terminal and collateral branching. Second, the turning capacity of growth cones (i.e., "choice" of a proper orientation) was impaired. In addition, lack of MAP1B may affect the post-translational modification of tubulin polymers: quantitative analysis showed a reduced amount of acetylated microtubules within growth cones, whereas the distribution of tyrosinated or detyrosinated microtubules was normal. Both growth cone turning and axonal branch formation are known to involve local regulation of the microtubule network. Our results demonstrate that MAP1B plays a role in these processes during plastic changes in the adult. In particular, the data suggest MAP1B implication in the locally coordinated assembly of cytoskeletal components required for branching and straight directional axon growth.

Expression of MAP1B protein and its phosphorylated form MAP1B-P in the CNS of a continuously growing fish, the rainbow trout.

Microtubule-associated protein-1B (MAP1B), and particularly its phosphorylated isoform MAP1B-P, play an important role in axonal outgrowth during development of the mammalian nervous system and have also been shown to be associated with axonal plasticity in the adult. Here, we used antibodies and mRNA probes directed against mammalian MAP1B to extend our analysis to fish species, trout (Oncorhynchus mykiss), at different stages of development. The specificity of the cross-reaction of our anti-total-MAP1B/MAP1B-P antibodies was confirmed by Western blotting. Trout MAP1B-like proteins exhibited about the same apparent molecular weight (320 kDa) as rat-MAP1B. Immunohistochemistry and in situ hybridization analysis performed on hindbrain and spinal cord revealed the presence of MAP1B in neurons and some glial subpopulations. Primary sensory neurons and motoneurons maintain high levels of MAP1B expression from early stages throughout adulthood, as has been shown for mammals. Unlike mammals, however, MAP1B and axon-specific MAP1B-P continue to be strongly expressed by hindbrain neurons projecting into spinal cord, with the important exception of Mauthner cells. MAP1B/MAP1B-P immunostaining were also detected elsewhere within the brain, including axons of the retino-tectal projection. This obvious difference between adult fish and mammals is likely to reflect the capacity of fish for continued growth and regeneration. Our results suggest that MAP1B/MAP1B-P expression is generally maintained in neurons known to regenerate after axotomy. The regenerative potential of the adult nervous system may in fact depend on continued expression of neuron-intrinsic growth related proteins, a feature of MAP1B that appears phylogenetically conserved.

Astrocytic and vascular remodeling in the injured adult rat spinal cord after chondroitinase ABC treatment.

Upregulation of extracellular chondroitin sulfate proteoglycans (CSPG) is a primary cause for the failure of axons to regenerate after spinal cord injury (SCI), and the beneficial effect of their degradation by chondroitinase ABC (ChABC) is widely documented. Little is known, however, about the effect of ChABC treatment on astrogliosis and revascularization, two important factors influencing axon regrowth. This was investigated in the present study. Immediately after a spinal cord hemisection at thoracic level 8-9, we injected ChABC intrathecally at the sacral level, repeated three times until 10 days post-injury. Our results show an effective cleavage of CSPG glycosaminoglycan chains and stimulation of axonal remodeling within the injury site, accompanied by an extended period of astrocyte remodeling (up to 4 weeks). Interestingly, ChABC treatment favored an orientation of astrocytic processes directed toward the injury, in close association with axons at the lesion entry zone, suggesting a correlation between axon and astrocyte remodeling. Further, during the first weeks post-injury, ChABC treatment affected the morphology of laminin-positive blood vessel basement membranes and vessel-independent laminin deposits: hypertrophied blood vessels with detached or duplicated basement membrane were more numerous than in lesioned untreated animals. In contrast, at later time points, laminin expression increased and became more directly associated with newly formed blood vessels, the size of which tended to be closer to that found in intact tissue. Our data reinforce the idea that ChABC injection in combination with other synergistic treatments is a promising therapeutic strategy for SCI repair.

Ensaio sobre a melancolia: suas origens, sua dialética, seus caminhos tortuosos e seu destino inelutável / Essay on melancholy: its origins, dialectic, winding paths, and ineluctable destiny / Ensayo sobre la melancolía: sus orígenes, su dialéctica, sus caminos tortuosos y su destino ineluctable

Inspirada pela leitura do filósofo Giorgio Agamben, a autora faz uma reflexão sobre a genealogia da melancolia, a partir de referências patrísticas da época medieval - que a designavam "acidia" -, de associações com a cosmologia ocidental e de distintas teorias no decorrer da história, até suas expressões na atualidade. O cerne do trabalho respalda-se em Freud, em "Luto e melancolia", e na leitura peculiar de Agamben, que, ao cotejar a interpretação psicanalítica do mecanismo da melancolia com o complexo humoral saturnino, destaca dois elementos descritos na acidia: o recesso do objeto e o retirar-se em si mesmo da intenção contemplativa. A autora aborda os conceitos de relações de objeto, fetichismo e narcisismo para esclarecer a dialética das relações, sua tortuosa intenção em busca do objeto e a natureza melancólica que subjaz na sombra desses processos.

Inspired by the work of the Italian philosopher Giorgio Agamben, the author ponders over the genealogy of melancholy, starting from patristics references in the Middle Ages - when it was termed "acedia" -, passing through associations with western cosmology and other theories throughout history, to its current expressions. The core of this paper is based on Freud's work "Mourning and melancholy" and on the peculiar review made by Giorgio Agamben. By comparing psychoanalytic understanding of the mechanism of melancholy with the saturnine humoral complex, Agamben emphasizes two elements of acedia: recess of the object and a self-alienation from the contemplative intention. The author also writes about concepts of object relations, fetichism and narcissism, in order to clarify the relational dialectic, its tortuous intent to pursue the object, and the melancholic nature underlying these processes.

Inspirada por las obras del filósofo Giorgio Agamben, la autora hace una reflexión sobre la genealogía de la melancolía, a partir de referencias patrísticas de la época medieval - que la denominaban "acedia" -, asociaciones con la cosmología occidental y distintas teorías surgidas en el transcurso de la historia, hasta llegar a sus manifestaciones actuales. Este trabajo se respalda en Freud - "Luto y melancolía" - y en la particular lectura de Agamben, que, al cotejar la interpretación psicoanalítica del mecanismo de la melancolía con el complejo humoral saturnino, destaca dos elementos descritos en la acedia: el receso del objeto y el retirarse en sí mismo de la intención contemplativa. La autora aborda los conceptos de las relaciones de objeto, del fetichismo y del narcisismo para aclarar la dialéctica de las relaciones, su tortuosa intención en busca del objeto y la naturaleza melancólica que subyaz en la sombra de esos procesos.

Extensive structural remodeling of the injured spinal cord revealed by phosphorylated MAP1B in sprouting axons and degenerating neurons.

Spinal cord injury (SCI) results in loss of sensory and motor function because injured axons do not regenerate and neurons that die are not replaced. Nevertheless, there is evidence for spontaneous reorganization of spared pathways (i.e. sprouting) that could be exploited to improve functional recovery. The extent of morphological remodeling after spinal cord injury is, however, not understood. We have previously shown that a phosphorylated form of microtubule-associated protein-1B, MAP1B-P, is expressed by growing axons, but is detected in intact adult SC in fibers exhibiting a somatotopic distribution of myelinated sensory fibers. We now demonstrate that after adult SCI, MAP1B-P is up-regulated in other classes of axons. We used immunohistochemistry to show changing levels and distributions of MAP1B-P after a right thoracic hemisection of adult rat spinal cord. MAP1B-P labeling suggests rearrangements of the axonal circuitry that go well beyond previous descriptions. MAP1B-P-positive fibers are present in ectopic locations in gray matter in both dorsal and ventral horns and around the central canal. Double staining reveals that primary sensory and descending serotonergic and corticospinal axons are MAP1B-P positive. In white matter, high MAP1B-P expression is found on terminal enlargements near the injury, reflecting retraction of transected axons. MAP1B-P also accumulates in pre-apoptotic neuronal somata axotomized by the lesion, indicating association of MAP1B-P not only with axon extension and retraction, but also with neuronal degeneration. Finally, we provide evidence that MAP1B phosphorylation is correlated with activation of JNK MAP-kinase, providing a step towards unraveling the mechanisms of regulation of this plasticity-related cytoskeletal protein.

Spinal cord injury-induced up-regulation of AHNAK, expressed in cells delineating cystic cavities, and associated with neoangiogenesis.

To investigate the molecular basis for the poor regenerative capacity of the mammalian central nervous system (CNS) after injury, we searched for genes whose expression was affected by an adult rat spinal cord hemi-section. Differential screening of a rat spinal cord expression library was performed using polyclonal antibodies raised against lesioned spinal cord tissue. A striking overexpression was found for ahnak, encoding a 700-kDa protein, in normal CNS present only in the blood-brain barrier (BBB) forming vascular endothelial cells. Indeed, very early after spinal cord injury (SCI), high levels of membrane-associated AHNAK are observed on non-neuronal cells invading the lesion site. With time, AHNAK distribution spreads rostrally and caudally concomitant with the process of tissue inflammation and axon degeneration, delineating the interior surface of cystic cavities, mainly in front of barrier-forming astrocytes. Strong overexpression is also observed on vascular endothelial cells reacting to BBB breakdown. Based on our detailed analysis of its spatiotemporal and cellular expression, and its previously described function in BBB, we suggest that AHNAK expression is associated with cell types displaying tissue-protective barrier properties. Our study may thus contribute to the elucidation of the precise molecular and cellular events that eventually render traumatic spinal cord tissue non-permissive for regeneration.

Neuronal and glial expression of the adhesion molecule TAG-1 is regulated after peripheral nerve lesion or central neurodegeneration of adult nervous system.

Expression of the cell adhesion molecule TAG-1 is down-regulated in adult brain, with the exception of certain areas exhibiting structural plasticity. Here, we present evidence that TAG-1 expression persists also in adult rat spinal cord and dorsal root ganglia (DRG), and can be up-regulated after injury. On Western blots of adult tissue, TAG-1 is detected as a 135-kDa band, with an additional specific 90-kDa band, not present in developing tissue. TAG-1 expression is found both in DRG neurons and in Schwann cells, particularly those associated with the peripherally projecting DRG processes. Quantitative in situ hybridization revealed that TAG-1 expression is significantly higher in small neurons that give rise to unmyelinated fibers, than in large DRG neurons. The regulation of TAG-1 was then examined in two different lesion paradigms. After a sciatic nerve lesion, TAG-1 expression is not up-regulated in DRG neurons, but decreases with time. At the lesion site, reactive Schwann cells up-regulate TAG-1, as demonstrated by both immunohistochemistry and in situ hybridization. In a second paradigm, we injected kainic acid into the spinal cord that kills neurons but spares glia and axons. TAG-1 is up-regulated in the spinal neuron-depleted area as well as in the corresponding dorsal and ventral roots, associated with both target-deprived afferent fibers and with the non-neuronal cells that invade the lesion site. These results demonstrate a local up-regulation of TAG-1 in the adult that is induced in response to injury, suggesting its involvement in axonal re-modelling, neuron-glia interactions, and glial cell migration.

Phosphorylated MAP1B is induced in central sprouting of primary afferents in response to peripheral injury but not in response to rhizotomy.

A peripheral nerve lesion induces sprouting of primary afferents from dorsal root ganglion (DRG) neurons into lamina II of the dorsal horn. Modifications of the environment in consequence to the axotomy provide an extrinsic stimulus. A potential neuron-intrinsic factor that may permit axonal sprouting is microtubule-associated protein 1B (MAP1B) in a specific phosphorylated form (MAP1B-P), restricted to growing or regenerating axons. We show here that both in rat and mouse, a sciatic nerve cut is rapidly followed by the appearance of MAP1B-P expression in lamina II, increasing to a maximum between 8 and 15 days, and diminishing after three months. Evidence is provided that sprouting and induction of MAP1B-P expression after peripheral injury are phenomena concerning essentially myelinated axons. This is in accordance with in situ hybridization data showing especially high MAP1B-mRNA levels in large size DRG neurons that give rise to myelinated fibers. We then employed a second lesion model, multiple rhizotomy with one spared root. In this case, unmyelinated CGRP expressing fibers do indeed sprout, but coexpression of MAP1B-P and CGRP is never observed in lamina II. Finally, because a characteristic of myelinated fibers is their high content in neurofilament protein heavy subunit (NF-H), we used NF-H-LacZ transgenic mice to verify that MAP1B-P induction and central sprouting were not affected by perturbing the axonal organization of neurofilaments. We conclude that MAP1B-P is well suited as a rapidly expressed, axon-intrinsic marker associated with plasticity of myelinated fibers.

Mash1 specifies neurons and oligodendrocytes in the postnatal brain.

Progenitors in the telencephalic subventricular zone (SVZ) remain mitotically active throughout life, and produce different cell types at embryonic, postnatal and adult stages. Here we show that Mash1, an important proneural gene in the embryonic telencephalon, is broadly expressed in the postnatal SVZ, in progenitors for both neuronal and oligodendrocyte lineages. Moreover, Mash1 is required at birth for the generation of a large fraction of neuronal and oligodendrocyte precursors from the olfactory bulb. Clonal analysis in culture and transplantation experiments in postnatal brain demonstrate that this phenotype reflects a cell-autonomous function of Mash1 in specification of these two lineages. The conservation of Mash1 function in the postnatal SVZ suggests that the same transcription mechanisms operate throughout life to specify cell fates in this structure, and that the profound changes in the cell types produced reflect changes in the signalling environment of the SVZ.