Establishing Myelinating Cocultures Using Human iPSC-Derived Sensory Neurons to Investigate Axonal Degeneration and Demyelination.

Complex signaling between Schwann cells and axons are vital for peripheral neuron development, myelination, and repair. The interaction between these two cell types can be modeled in vitro by coculturing rodent Schwann cells and neurons together. These have in the past been used with great success to help unravel the bidirectional signaling mechanisms that lead to Schwann cell proliferation and myelination. To provide more translatable potential, we have developed myelinating cocultures using human, induced pluripotent stem cell (iPSC)-derived neurons. Under the right conditions, the human neurons are efficiently myelinated by rat Schwann cells, demonstrating successful cross-species signaling. This chapter describes all the necessary steps to generate these myelinating cocultures and methods to investigate and quantify various aspects of myelination. The myelinating cocultures can be maintained in excellent health for over 1 year, facilitating their use to study developmental or chronic disease processes. With this in mind, we have used the cocultures to model a sensory neuropathy which displays clinically with both axonal and demyelinating features. In the cocultures, we found evidence of extensive axonal degeneration and demyelination demonstrated by axonal swelling and fragmentation, and myelin disintegration. The myelinating cocultures can therefore be used to study complex, human disease processes that result in both axonal and myelin-associated degenerative processes.

Glutamate Activates AMPA Receptor Conductance in the Developing Schwann Cells of the Mammalian Peripheral Nerves.

Schwann cells (SCs) are myelinating cells of the PNS. Although SCs are known to express different channels and receptors on their surface, little is known about the activation and function of these proteins. Ionotropic glutamate receptors are thought to play an essential role during development of SC lineage and during peripheral nerve injury, so we sought to study their functional properties. We established a novel preparation of living peripheral nerve slices with preserved cellular architecture and used a patch-clamp technique to study AMPA-receptor (AMPAR)-mediated currents in SCs for the first time. We found that the majority of SCs in the nerves dissected from embryonic and neonatal mice of both sexes respond to the application of glutamate with inward current mediated by Ca2+-permeable AMPARs. Using stationary fluctuation analysis (SFA), we demonstrate that single-channel conductance of AMPARs in SCs is 8-11 pS, which is comparable to that in neurons. We further show that, when SCs become myelinating, they downregulate functional AMPARs. This study is the first to demonstrate AMPAR-mediated conductance in SCs of vertebrates, to investigate elementary properties of AMPARs in these cells, and to provide detailed electrophysiological and morphological characterization of SCs at different stages of development.SIGNIFICANCE STATEMENT We provide several important conceptual and technical advances in research on the PNS. We pioneer the first description of AMPA receptor (AMPAR)-mediated currents in the PNS glia of vertebrates and provide new insights into the properties of AMPAR channels in peripheral glia; for example, their Ca2+ permeability and single-channel conductance. We describe for the first time the electrophysiological and morphological properties of Schwann cells (SCs) at different stages of development and show that functional AMPARs are expressed only in developing, not mature, SCs. Finally, we introduce a preparation of peripheral nerve slices for patch-clamp recordings. This preparation opens new possibilities for studying the physiology of SCs in animal models and in surgical human samples.

GABA and its B-receptor are present at the node of Ranvier in a small population of sensory fibers, implicating a role in myelination.

The γ-aminobutyric acid (GABA) type B receptor has been implicated in glial cell development in the peripheral nervous system (PNS), although the exact function of GABA signaling is not known. To investigate GABA and its B receptor in PNS development and degeneration, we studied the expression of the GABAB receptor, GABA, and glutamic acid decarboxylase GAD65/67 in both development and injury in fetal dissociated dorsal root ganglia (DRG) cell cultures and in the rat sciatic nerve. We found that GABA, GAD65/67, and the GABAB receptor were expressed in premyelinating and nonmyelinating Schwann cells throughout development and after injury. A small population of myelinated sensory fibers displayed all of these molecules at the node of Ranvier, indicating a role in axon-glia communication. Functional studies using GABAB receptor agonists and antagonists were performed in fetal DRG primary cultures to study the function of this receptor during development. The results show that GABA, via its B receptor, is involved in the myelination process but not in Schwann cell proliferation. The data from adult nerves suggest additional roles in axon-glia communication after injury.

Peripheral nervous system defects in a mouse model for peroxisomal biogenesis disorders.

Peroxisome biogenesis disorders (PBD) are autosomal recessive disorders in humans characterized by skeletal, eye and brain abnormalities. Despite the fact that neurological deficits, including peripheral nervous system (PNS) defects, can be observed at birth in some PBD patients including those with PEX10 mutations, the embryological basis of the PNS defects is unclear. Using a forward genetic screen, we identified a mouse model for Pex10 deficiency that exhibits neurological abnormalities during fetal development. Homozygous Pex10 mutant mouse embryos display biochemical abnormalities related to a PBD deficiency. During late embryogenesis, Pex10 homozygous mutant mice experience progressive loss of movement and at birth they become cyanotic and die shortly thereafter. Homozygous Pex10 mutant fetuses display decreased integrity of axons and synapses, over-extension of axons in the diaphragm and decreased Schwann cell numbers. Our neuropathological, molecular and electrophysiological studies provide new insights into the embryological basis of the PNS deficits in a PBD model. Our findings identify PEX10 function, and likely other PEX proteins, as an essential component of the spinal locomotor circuit.

Roles of chromatin remodelers in maintenance mechanisms of multipotency of mouse trunk neural crest cells in the formation of neural crest-derived stem cells.

We analyzed roles of two chromatin remodelers, Chromodomain Helicase DNA-binding protein 7 (CHD7) and SWItch/Sucrose NonFermentable-B (SWI/SNF-B), and Bone Morphogenetic Protein (BMP)/Wnt signaling in the maintenance of the multipotency of mouse trunk neural crest cells, leading to the formation of mouse neural crest-derived stem cells (mouse NCSCs). CHD7 was expressed in the undifferentiated neural crest cells and in the dorsal root ganglia (DRG) and sciatic nerve, typical tissues containing NCSCs. BMP/Wnt signaling stimulated the expression of CHD7 and participated in maintaining the multipotency of neural crest cells. Furthermore, the promotion of CHD7 expression maintained the multipotency of these cells. The inhibition of CHD7 and SWI/SNF-B expression significantly suppressed the maintenance of the multipotency of these cells. In addition, BMP/Wnt treatment promoted CHD7 expression and caused the increase of the percentage of multipotent cells in DRG. Thus, the present data suggest that the chromatin remodelers as well as BMP/Wnt signaling play essential roles in the maintenance of the multipotency of mouse trunk neural crest cells and in the formation of mouse NCSCs.

Anatomical relation between sciatic nerve and piriformis muscle and its bifurcation level during fetal period in human.

PURPOSE: The aim of this study is to determine the morphometric development, location and variant formations of the sciatic nerve using anatomic dissection method during the fetal period. METHODS: Sciatic nerves of 200 human fetuses (103 males and 97 females) aged between 9 and 40 weeks of gestation were studied bilaterally. The bifurcation level of the sciatic nerve to its terminal branches was evaluated with respect to popliteal fossa. Then the length of the sciatic nerve, starting from where it leaves the piriformis muscle till the bifurcation point of the nerve, and its width at the point where it leaves infrapiriforme foramen and its width at the bifurcation level were measured. We also measured the distance of the sciatic nerve to the ischial tuberosity, the greater trochanter and the intergluteal sulcus. Mean values and standard deviations of all parameters according to trimesters were calculated. RESULTS: We found that all parameters increase with age during the fetal period (P < 0.05). Parameters do not show any significant differences between sexes (P > 0.05). In our analysis, we observed that in 98 % of the cases (on the right and the left side) the sciatic nerve leaves the pelvis below the piriformis muscle. The remaining cases (2 %) are variant formations. CONCLUSION: We believe that our study will be useful for better understanding of sciatic nerve development and it may contribute to future studies in obstetrics, orthopedics and fetal pathology. Knowledge of variant formations of the sciatic nerve, its bifurcation level and its relation with neighboring structures may be important for blockade of the nerve in newborn surgeries.

Formation of the sural nerve in foetal cadavers.

The purpose of this study was to provide a morphologic description and assessment on the formation level of the sural nerve (SN) and its components. Also we aimed to reveal histological features of the SN components. An anatomical study of the formation of the SN was carried out on 100 limbs from 50 embalmed foetuses. The results showed that the SN was formed by the union of the medial sural cutaneous nerve (MSCN) and the peroneal communicating branch (PCB) in 71% of the cases (Type A); the MSCN and PCB are branches of the tibial and common peroneal nerve (CPN) or lateral sural cutaneous nerves (LSCN), respectively. Formation level of the SN was at the distal third of the leg in 43% of the cases, at the middle third of the leg in 46% of the cases, and at the upper third of the leg in 11% of the cases. The PCB originated in the CPN in 68% and the PCB originated in the LSCN in 3% of the cases. The SN was formed only by the MSCN in 20% of the cases (Type B). Type C was divided into four subgroups: in the first group the PCB and fibres of the posterior femoral cutaneous nerve joined the MSCN in 4% of cases; in the second group the MSCN, PCB, and sciatic nerve did not unite and coursed separately in 1% of cases; in the third group the SN arose directly from the sciatic nerve alone and the MSCN made a little contribution in 2% of cases; and in the fourth group the PCB, fibres of the sciatic nerve, and the MSCN formed the SN in 1% of the cases. The SN was formed only by the PCB in 1% of the cases (Type D). Distances of the formation level of the SN to the intercondylar line and the lateral malleolus were measured and also noted. A detailed knowledge of the anatomy of the SN and its contributing nerves are important in many interventional procedures.

BD PuraMatrix peptide hydrogel as a culture system for human fetal Schwann cells in spinal cord regeneration.

BD PuraMatrix peptide hydrogel, a three-dimensional cell culture model of nanofiber scaffold derived from the self-assembling peptide RADA16, has been applied to regenerative tissue repair in order to develop novel nanomedicine systems. In this study with PuraMatrix, self-assembling nanofiber scaffold (SAPNS) and Schwann cells (SCs) were isolated from human fetal sciatic nerves, cultured within SAPNS, and then transplanted into the spinal cord after injury (SCI) in rats. First, the peptide nanofiber scaffold was evaluated via scanning electron microscopy and atomic force microscopy. With phase-contrast microscopy, the appearance of representative human fetal SCs encapsulated in PuraMatrix on days 3, 5, and 7 in 12-well plates was revealed. The Schwann cells in PuraMatrix were cultured for 2 days, and the SCs had active proliferative potential. Spinal cord injury was induced by placing a 35-g weight on the dura of T9-T10 segments for 15 min, followed by in vivo treatment with SAPNS and human fetal SCs (100,000 cells/10 µl/injection) grafted into spinal cord 7 days after SCI. After treatment, the recovery of motor function was assessed periodically using the Basso, Beattie, and Bresnahan scoring system. Eight weeks after grafting, animals were perfusion fixed, and the survival of implanted cells was analyzed with antibody recognizing SCs. Immunohistochemical analysis of grafted lumber segments at 8 weeks after grafting revealed reduced asterogliosis and considerably increased infiltration of endogenous S100(+) cells into the injury site, suggesting that PuraMatrix may play an important role in the repair observed after SAPNS and human fetal SC transplantation.

The topographical features and variations of nervus ischiadicus in human fetuses.

BACKGROUND: We aimed to investigate the topographical features and variations of ischiadic nerve during prenatal period in human. METHODS: Our study was conducted on lower extremities of 34 human fetal cadavers who were free of any anomalies and were obtained from the department of pathology of our faculty. RESULTS: When the development of topographical features of ischiadic nerve is considered according to the gestational weeks, it was shown that the distances increased in accordance with the age and there was a positive correlation between the two (p < 0.01), however the width of the ischiadic nerve did not increase similarly and there was no significant correlation between its width and the age (p > 0.01). CONCLUSIONS: Understanding the structure and course of ischiadic nerve in both gluteal and femoral regions is important during all interventions to these regions due to the potential damage on the nerve itself. The knowledge of topographical features of ischiadic nerve in the prenatal period and its relations with reference points that are used especially in childhood and adults will help to follow up the variations during postnatal and grow up periods (Tab. 2, Fig. 4, Ref. 13).

The effects of valproic acid on sciatic nerve of fetal rats and protective effects of folic acid and vitamin E / Efectos del ácido valproico sobre el nervio ciático de fetos de ratas y efectos de protección del ácido fólico y vitamina E

We aimed to investigate the potential harmful effects of maternal valproic acid (VPA) on fetal sciatic nerve, and the protective effects of vitamin E (Vit E) and folic acid (FA) on fetal rats. Valproic acid (400mg/kg), folic acid (400mg/kg) and vitamin E (250 mg/kg) were administered to rats on each of gestation days 8-10. All fetuses were collected on gestation day 20. With thin sections of biopsies, sciatic nerve of fetuses were stained with uranyl acetat and were examined under transmission electron microscope. The fetuses (n:36) were divided into five groups: control, vpa, vpa+fa, vpa+vit e and vpa+fa+vit e groups. In each group; drug procedure, surgical procedure and histological methods were performed. Later, weights and lengths of fetuses in each group were compared and analyzed by One-Way Anova test. Administration of single doses of valproic acid (400 mg/kg) resulted in weight and length loss between control and vpa group. However, length and weight differences between the other groups were not significant. The histopathological findings of control group was normal. In vpa group, it showed extensive degenerative changes especially in myelin coat. In addition, most prominent finding in this group was condensation of collagen fibers in extensively demyelinated samples, while moderately effected areas were relatively normal. Both vpa+fa and vpa+ vit e groups exhibited similar ultrastructural changes, reflecting minimal to moderate degenerative changes. In vpa+fa+vit e group had almost the normal structure. Administration of single doses of valproic acid (400 mg/kg) resulted in a deteriorative effect on sciatic nerve at ultrastructural level. Administration of FA and Vit E had a protective effect to prevent the degenerative changes to a certain degree. Combination of FA and Vit E together following VPA administration had a more potent protective effect. The objective of the present study is to analyze histopathologic changes which ...

El objetivo fue investigar los posibles efectos perjudiciales del ácido valproico (AVP) materno sobre el nervio ciático en fetos y los efectos protectores de la vitamina E (Vit E) y ácido fólico (AF) en fetos de ratas. Se administraron a ratas ácido valproico (400mg/kg), ácido fólico (400mg/kg) y vitamina E (250 mg/kg) en cada uno de los días de gestación 8-10. Todos los fetos fueron recogidos a los 20 días de gestación. Finas secciones de biopsias obtenidas de los nervios ciáticos de fetos fueron teñidos con acetato de uranilo y examinados bajo microscopio electrónico de transmisión. Los fetos (n: 36) fueron divididos en cinco grupos: control, avp, avp+af, avp+vit e y avp+fa+vit e. En cada grupo, se realizaron los procedimientos farmacológicos, quirúrgicos y los métodos histológicos. Los pesos y longitudes de los fetos de cada grupo fueron comparados y analizados usando la prueba One-Way Anova. La administración de dosis únicas de ácido valproico (400 mg / kg) resultó en la pérdida del peso la longitud entre el control y el grupo apv. Sin embargo, las diferencias en la longitud y el peso entre los otros grupos no fueron significativas. Los hallazgos histopatológicos del grupo control fueron normales. En el grupo avp, se mostró especialmente cambios degenerativos en la mielina que envuelve al nervio periféricamente. Además, predominatemente se encontró en las muestras de este grupo fibras colágenas condensadas y zonas ampliamente desmielinizadas, mientras que las zonas moderadamente afectadas eran relativamente normales. Ambos grupos avp+fa y avp+vit e exhibieron cambios ultraestructurales similares, lo que supone un mínimo o moderado cambio degenerativo. El grupo avp+fa+vit e tuvo casi una estructura normal. La administración de dosis únicas de ácido valproico (400 mg / kg) produjo un efecto sobre el deterioro del nervio ciático a nivel ultraestructural. La administración de la AF y vitamina E tienen un efecto protector, en cierta medida, ...

Expression and localization of Ski determine cell type-specific TGFbeta signaling effects on the cell cycle.

Transforming growth factor beta (TGFbeta) promotes epithelial cell differentiation but induces Schwann cell proliferation. We show that the protooncogene Ski (Sloan-Kettering viral oncogene homologue) is an important regulator of these effects. TGFbeta down-regulates Ski in epithelial cells but not in Schwann cells. In Schwann cells but not in epithelial cells, retinoblastoma protein (Rb) is up-regulated by TGFbeta. Additionally, both Ski and Rb move to the cytoplasm, where they partially colocalize. In vivo, Ski and phospho-Rb (pRb) appear to interact in the Schwann cell cytoplasm of developing sciatic nerves. Ski overexpression induces Rb hyperphosphorylation, proliferation, and colocalization of both proteins in Schwann cell and epithelial cell cytoplasms independently of TGFbeta treatment. Conversely, Ski knockdown in Schwann cells blocks TGFbeta-induced proliferation and pRb cytoplasmic relocalization. Our findings reveal a critical function of fine-tuned Ski levels in the control of TGFbeta effects on the cell cycle and suggest that at least a part of Ski regulatory effects on TGFbeta-induced proliferation of Schwann cells is caused by its concerted action with Rb.

Induction of abnormal proliferation by nonmyelinating schwann cells triggers neurofibroma formation.

Recent evidence suggests that alterations in the self-renewal program of stem/progenitor cells can cause tumorigenesis. By utilizing genetically engineered mouse models of neurofibromatosis type 1 (NF1), we demonstrated that plexiform neurofibroma, the only benign peripheral nerve sheath tumor with potential for malignant transformation, results from Nf1 deficiency in fetal stem/progenitor cells of peripheral nerves. Surprisingly, this did not cause hyperproliferation or tumorigenesis in early postnatal period. Instead, peripheral nerve development appeared largely normal in the absence of Nf1 except for abnormal Remak bundles, the nonmyelinated axon-Schwann cell unit, identified in postnatal mutant nerves. Subsequent degeneration of abnormal Remak bundles was accompanied by initial expansion of nonmyelinating Schwann cells. We suggest abnormally differentiated Remak bundles as a cell of origin for plexiform neurofibroma.

Induction of neuronal and myelin-related gene expression by IL-6-receptor/IL-6: a study on embryonic dorsal root ganglia cells and isolated Schwann cells.

The conditional knockdown of the Interleukin-6 (IL-6) family signal transducer (gp130) causes peripheral nerve demyelination and degeneration. In the present work, we investigated the effect of gp130 signaling on peripheral nerves and Schwann cells (SC). We stimulated gp130 signaling with IL6RIL6, a fusion molecule of IL-6 and IL-6R, in rat embryonic day 14 dorsal root ganglia (DRG) cell cultures. In neurons, IL6RIL6 strongly increased the axonal network. In SC, IL6RIL6 favored the appearance of elongated more mature cells versus stellar shaped cells. Gene expression profiling showed an increased expression of neuronal and glial-specific genes. mRNAs related to SC function, including myelin-specific genes, were increased by IL6RIL6 treatment of DRG cells, or of purified SCs isolated from rat sciatic nerve. In IL6RIL6-treated cells, immunostaining showed a strong nuclear signal for Krox-20, a transcription factor essential for differentiation of the SC lineage. On the contrary, we observed that IL6RIL6 inhibited the genes related to TGF-beta family as well as the production of smooth muscle actin.

The mRNA of transferrin is expressed in Schwann cells during their maturation and after nerve injury.

Transferrin, the iron carrier protein, has been shown to be involved in oligodendroglial cell differentiation in the central nervous system but little is known about its role in the peripheral nervous system. In the present work, we have studied the presence of transferrin and of its mRNA in rat sciatic nerves and in Schwann cells isolated at embryonic and adult ages as well as during the regeneration process that follows nerve crush. We have also studied the correlation between the expression of the mRNAs of transferrin and the expression of mature myelin markers in the PNS. We show that transferrin is present in whole sciatic nerves at late stages of embryonic life as well as at postnatal day 4 and in adult rats. We demonstrate for the first time, that in normal conditions, the transferrin mRNA is expressed in Schwann cells isolated from sciatic nerves between embryonic days 14 and 18, being absent at later stages of development and in adult animals. In adult rats, 3 days after sciatic nerve crushing, the mRNA of transferrin is expressed in the injured nerve, but 7 days after injury its expression disappears. Transferrin protein in the sciatic nerve closely follows the expression of its mRNA indicating that under these circumstances, it appears to be locally synthesized. Transferrin in the PNS could have a dual role. During late embryonic ages it could be locally synthesized by differentiating Schwann cells, acting as a pro-differentiating factor. A similar situation would occur during the regeneration that follows Wallerian degeneration. In the adult animals on the other hand, Schwann cells could pick up transferrin from the circulation or/and from the axons, sub serving possible trophic actions closely related to myelin maintenance.

Action of Schwann cells implanted in cerebral hemorrhage lesion.

OBJECTIVE: To investigate whether there is neogenesis of myelin sheath and neuron after transplantation of Schwann cells into cerebral hemorrhage lesion. METHODS: Schwann cells were expanded, labeled with BrdU in vitro and transplanted into rat cerebral hemorrhage with blood extracted from femoral artery and then injected into the basal nuclei. Double immunohistochemistry staining and electron microscopy were used to detect the expression of BrdU/MBP and BrdU/GAP-43 and remyelination. RESULTS: BrdU/MBP double positive cells could be seen at 1 week up to 16 weeks after transplantation of Schwann cells. Thin remyelination was observed under electron microscope. GAP-43 positive cells appeared after 12 weeks and were found more in Hippocamp. CONCLUSIONS: Grafted Schwann cells participate in remyelination and promoter nerve restore in rat cerebral hemorrhage.

TGFbeta type II receptor signaling controls Schwann cell death and proliferation in developing nerves.

During development, Schwann cell numbers are precisely adjusted to match the number of axons. It is essentially unknown which growth factors or receptors carry out this important control in vivo. Here, we tested whether the type II transforming growth factor (TGF) beta receptor has a role in this process. We generated a conditional knock-out mouse in which the type II TGFbeta receptor is specifically ablated only in Schwann cells. Inactivation of the receptor, evident at least from embryonic day 18, resulted in suppressed Schwann cell death in normally developing and injured nerves. Notably, the mutants also showed a strong reduction in Schwann cell proliferation. Consequently, Schwann cell numbers in wild-type and mutant nerves remained similar. Lack of TGFbeta signaling did not appear to affect other processes in which TGFbeta had been implicated previously, including myelination and response of adult nerves to injury. This is the first in vivo evidence for a growth factor receptor involved in promoting Schwann cell division during development and the first genetic evidence for a receptor that controls normal developmental Schwann cell death.

The instability of the neural crest phenotypes: Schwann cells can differentiate into myofibroblasts.

In the vertebrate embryo, the neural crest cells (NCCs) that migrate out from the neural primordium yield multiple phenotypes, including melanocytes, peripheral neurones and glia and, in the head, cartilage, bone, connective cells and myofibroblasts / vascular smooth muscle cells (SMCs). The differentiation of pluripotent NCCs is mainly directed by local growth factors. Even at postmigratory stages, NC-derived cells exhibit some fate plasticity. Thus, we reported earlier that pigment cells and Schwann cells are able in vitro to interconvert in the presence of endothelin 3 (ET3). Here, we further investigated the capacity of Schwann cells to reprogram their phenotype. We show that purified quail Schwann cells in dissociated cultures produce alpha smooth muscle actin ((alpha)SMA)-expressing myofibroblasts through the generation of a pluripotent progeny. This transdifferentiation took place independently of ET3, but was promoted by transforming growth factor beta1 (TGF(beta)1). Moreover, when implanted into chick embryos, the Schwann cells were found to contribute with host cephalic NCCs to perivascular SMCs. These data provided the first evidence for the acquisition of an NC-derived mesenchymal fate by Schwann cells and further demonstrate that the differentiation state of NC-derived cells is unstable and capable of reprogramming. The high plasticity of Schwann cells evidenced here also suggests that, as in the CNS, glial cells of the PNS may function as NC stem cells in particular circumstances such as repair.

Conditional beta1-integrin gene deletion in neural crest cells causes severe developmental alterations of the peripheral nervous system.

Integrins are transmembrane receptors that are known to interact with the extracellular matrix and to be required for migration, proliferation, differentiation and apoptosis. We have generated mice with a neural crest cell-specific deletion of the beta1-integrin gene to analyse the role of beta1-integrins in neural crest cell migration and differentiation. This targeted mutation caused death within a month of birth. The loss of beta1-integrins from the embryo delayed the migration of Schwann cells along axons and induced multiple defects in spinal nerve arborisation and morphology. There was an almost complete absence of Schwann cells and sensory axon segregation and defective maturation in neuromuscular synaptogenesis. Thus, beta1-integrins are important for the control of embryonic and postnatal peripheral nervous system development.

The temporospatial expression of peripheral myelin protein 22 at the developing blood-nerve and blood-brain barriers.

Peripheral myelin protein 22 (PMP22), also known as growth arrest-specific gene 3 (gas3), is a tetraspan membrane protein whose misexpression is associated with demyelinating peripheral neuropathies. Although the function of PMP22 in Schwann cells is unknown, the protein is found at intercellular junctions of various epithelia and endothelia. To begin to elucidate the role of PMP22 at cell junctions, we examined the temporal expression and protein localization during development and maturation of the rat blood-nerve barrier (BNB) and blood-brain barrier (BBB). Developing and adult rat sciatic nerves and brains were coimmunostained for PMP22 and known junctional proteins including zonula occludens-1 (ZO-1), occludin, and claudin-5. Prior to the maturation of the BNB and BBB and detection of the tight junction protein occludin, PMP22 is present at ZO-1 positive endothelial junctions of the sciatic nerve and brain cortex. The subcellular localization of PMP22 in cultured brain endothelia was confirmed by internalization with ZO-1 after EGTA-induced disruption of cell junctions. In choroid epithelia, PMP22 is detected along with occludin and ZO-1 as early as embryonic day 15 (E15). In agreement, PMP22 message is elevated in P1 rat brain microvasculature and choroid epithelia, compared with total cortex. Additionally, neuroepithelial cell junctions in the embryonic rat brain are immunoreactive for PMP22, ZO-1, and beta-catenin but not occludin. Together, these studies identify PMP22 as an early constituent of intercellular junctions in the developing and mature rat BNB and BBB.

Involvement of gicerin, a cell adhesion molecule, in development and regeneration of chick sciatic nerve.

We have examined the role of gicerin, an immunoglobulin superfamily cell adhesion molecule, in chick sciatic nerves during development and regeneration. Gicerin was expressed in the spinal cord, dorsal root ganglion (DRG) and sciatic nerves in embryos, but declined after hatching. Neurite extensions from explant cultures of the DRG were promoted on gicerin's ligands, which were inhibited by an anti-gicerin antibody. Furthermore, gicerin expression was upregulated in the regenerating sciatic nerves, DRG and dorsal horn of the spinal cord after injury to the sciatic nerve. These results indicate that gicerin might participate in the development and regeneration of sciatic nerves.