Postnatal Central Nervous System Research Articles

Postnatal Systemic Inflammation Exacerbates Impairment of Hippocampal Synaptic Plasticity in an Animal Seizure Model

Objective: To investigate the effects of systemic inflammation in the critical postnatal stages on neurophysiological actions of immune processes and neural plasticity in adult rats after kainic acid (KA)-induced seizures. Methods: To determine changes in hippocampal synaptic plasticity after postnatal central nervous system inflammatory responses and seizure attacks, we performed intraperitoneal injections of lipopolysaccharide (LPS) in postnatal Sprague Dawley rats on day 14 (P14) to induce central nervous system inflammation. We then used a KA tail vein injection on P35 to induce seizure attacks. We compared the variability in synaptic plasticity in the hippocampal Schaffer collateral-CA1 region of seizure animals with or without LPS-induced inflammation preconditioning. Results: P14 injection of LPS increased susceptibility to seizures, while treatment with KA on P35 induced seizures. Long-term potentiation (LTP) of the Schaffer collateral-CA1 region was impaired in seizure animals, and this effect was more pronounced in the P14 LPS injection group. Fluoro-Jade staining revealed an increase in degenerated hippocampal CA1 pyramidal cells in the P14 LPS injection group. Cytokine expression in the hippocampus in the pre-, peri- and postictus periods was greater in P14 LPS rats than in saline-treated rats. Conclusions: Intraperitoneal LPS injection on P14 induces higher cytokine secretion after KA-induced seizures, enhancing neuronal excitability, shortening seizure onset time and exacerbating neuronal degeneration and impairment of LTP formation in the hippocampal Schaffer collateral-CA1 region. Central nervous system inflammation during critical stages of childhood development could disrupt the balance needed for neurophysiological actions of immune processes, producing direct, pernicious effects on memory, neural plasticity and neurogenesis into adulthood.

Use of “MGE Enhancers” for Labeling and Selection of Embryonic Stem Cell-Derived Medial Ganglionic Eminence (MGE) Progenitors and Neurons

The medial ganglionic eminence (MGE) is an embryonic forebrain structure that generates the majority of cortical interneurons. MGE transplantation into specific regions of the postnatal central nervous system modifies circuit function and improves deficits in mouse models of epilepsy, Parkinson's disease, pain, and phencyclidine-induced cognitive deficits. Herein, we describe approaches to generate MGE-like progenitor cells from mouse embryonic stem (ES) cells. Using a modified embryoid body method, we provided gene expression evidence that mouse ES-derived Lhx6+ cells closely resemble immature interneurons generated from authentic MGE-derived Lhx6+ cells. We hypothesized that enhancers that are active in the mouse MGE would be useful tools in detecting when ES cells differentiate into MGE cells. Here we demonstrate the utility of enhancer elements [422 (DlxI12b), Lhx6, 692, 1056, and 1538] as tools to mark MGE-like cells in ES cell differentiation experiments. We found that enhancers DlxI12b, 692, and 1538 are active in Lhx6-GFP+ cells, while enhancer 1056 is active in Olig2+ cells. These data demonstrate unique techniques to follow and purify MGE-like derivatives from ES cells, including GABAergic cortical interneurons and oligodendrocytes, for use in stem cell-based therapeutic assays and treatments.

Tumor suppressive pathways in the control of neurogenesis.

The generation of specialized neural cells in the developing and postnatal central nervous system is a highly regulated process, whereby neural stem cells divide to generate committed neuronal progenitors, which then withdraw from the cell cycle and start to differentiate. Cell cycle checkpoints play a major role in regulating the balance between neural stem cell expansion and differentiation. Loss of tumor suppressors involved in checkpoint control can lead to dramatic alterations of neurogenesis, thus contributing to neoplastic transformation. Here we summarize and critically discuss the existing literature on the role of tumor suppressive pathways and their regulatory networks in the control of neurogenesis and transformation.

Programming and reprogramming neuronal subtypes in the central nervous system

Recent discoveries in nuclear reprogramming have challenged the dogma that the identity of terminally differentiated cells cannot be changed. The identification of molecular mechanisms that reprogram differentiated cells to a new identity carries profound implications for regenerative medicine across organ systems. The central nervous system (CNS) has historically been considered to be largely immutable. However, recent studies indicate that even the adult CNS is imparted with the potential to change under the appropriate stimuli. Here, we review current knowledge regarding the capability of distinct cells within the CNS to reprogram their identity and consider the role of developmental signals in directing these cell fate decisions. Finally, we discuss the progress and current challenges of using developmental signals to precisely direct the generation of individual neuronal subtypes in the postnatal CNS and in the dish.

Identification of a novel intronic enhancer responsible for the transcriptional regulation of musashi1 in neural stem/progenitor cells

BackgroundThe specific genetic regulation of neural primordial cell determination is of great interest in stem cell biology. The Musashi1 (Msi1) protein, which belongs to an evolutionarily conserved family of RNA-binding proteins, is a marker for neural stem/progenitor cells (NS/PCs) in the embryonic and post-natal central nervous system (CNS). Msi1 regulates the translation of its downstream targets, including m-Numb and p21 mRNAs. In vitro experiments using knockout mice have shown that Msi1 and its isoform Musashi2 (Msi2) keep NS/PCs in an undifferentiated and proliferative state. Msi1 is expressed not only in NS/PCs, but also in other somatic stem cells and in tumours. Based on previous findings, Msi1 is likely to be a key regulator for maintaining the characteristics of self-renewing stem cells. However, the mechanisms regulating Msi1 expression are not yet clear.ResultsTo identify the DNA region affecting Msi1 transcription, we inserted the fusion gene ffLuc, comprised of the fluorescent Venus protein and firefly Luciferase, at the translation initiation site of the mouse Msi1 gene locus contained in a 184-kb bacterial artificial chromosome (BAC). Fluorescence and Luciferase activity, reflecting the Msi1 transcriptional activity, were observed in a stable BAC-carrying embryonic stem cell line when it was induced toward neural lineage differentiation by retinoic acid treatment. When neuronal differentiation was induced in embryoid body (EB)-derived neurosphere cells, reporter signals were detected in Msi1-positive NSCs and GFAP-positive astrocytes, but not in MAP2-positive neurons. By introducing deletions into the BAC reporter gene and conducting further reporter experiments using a minimized enhancer region, we identified a region, "D5E2," that is responsible for Msi1 transcription in NS/PCs.ConclusionsA regulatory element for Msi1 transcription in NS/PCs is located in the sixth intron of the Msi1 gene. The 595-bp D5E2 intronic enhancer can transactivate Msi1 gene expression with cell-type specificity markedly similar to the endogenous Msi1 expression patterns.

Optimization of a 96-Well Electroporation Assay for Postnatal Rat CNS Neurons Suitable for Cost–Effective Medium-Throughput Screening of Genes that Promote Neurite Outgrowth

Following an injury, central nervous system (CNS) neurons show a very limited regenerative response which results in their failure to successfully form functional connections with their original target. This is due in part to the reduced intrinsic growth state of CNS neurons, which is characterized by their failure to express key regeneration-associated genes (RAGs) and by the presence of growth inhibitory molecules in CNS environment that form a molecular and physical barrier to regeneration. Here we have optimized a 96-well electroporation and neurite outgrowth assay for postnatal rat cerebellar granule neurons (CGNs) cultured upon an inhibitory cellular substrate expressing myelin-associated glycoprotein or a mixture of growth inhibitory chondroitin sulfate proteoglycans. Optimal electroporation parameters resulted in 28% transfection efficiency and 51% viability for postnatal rat CGNs. The neurite outgrowth of transduced neurons was quantitatively measured using a semi-automated image capture and analysis system. The neurite outgrowth was significantly reduced by the inhibitory substrates which we demonstrated could be partially reversed using a Rho Kinase inhibitor. We are now using this assay to screen large sets of RAGs for their ability to increase neurite outgrowth on a variety of growth inhibitory and permissive substrates.

Visual Activity Regulates Neural Progenitor Cells in Developing Xenopus CNS through Musashi1

Regulation of progenitor cell fate determines the numbers of neurons in the developing brain. While proliferation of neural progenitors predominates during early central nervous system (CNS) development, progenitor cell fate shifts toward differentiation as CNS circuits develop, suggesting that signals from developing circuits may regulate proliferation and differentiation. We tested whether activity regulates neurogenesis invivo in the developing visual system of Xenopus tadpoles. Both cell proliferation and the number of musashi1-immunoreactive progenitors in the optic tectum decrease as visual system connections become stronger. Visual deprivation for 2days increased proliferation of musashi1-immunoreactive radial glial progenitors, while visual experience increased neuronal differentiation. Morpholino-mediated knockdown and overexpression of musashi1 indicate that musashi1 is necessary and sufficient for neural progenitor proliferation in the CNS. These data demonstrate a mechanism by which increased brain activity in developing circuits decreases cell proliferation and increases neuronal differentiation through the downregulation of musashi1 in response to circuit activity.

Effect of neuronal precursor cells derived from medial ganglionic eminence in an acute epileptic seizure model

Most of the gamma-aminobutyric acid (GABA)ergic interneurons in the cerebral cortex originate from restricted regions of the ventral telencephalon known as the caudal and medial ganglionic eminence (MGE) and from the preoptic area. It is well established that dysfunction of GABAergic interneurons can lead to epilepsy. During the last decade new approaches to prevent, reduce, or reverse the epileptic condition have been studied, including cell-based therapy from different sources. Recent studies have shown that transplanted neuronal precursor cells derived from MGE have the ability to migrate, differentiate into inhibitory GABAergic interneurons, and integrate into cortical and hippocampal networks, modifying the inhibitory tone in the host brain. Therefore, transplantation of neuronal precursors derived from MGE into the postnatal central nervous system (CNS) could modify the neuronal circuitry in neurologic diseases in which inhibitory synaptic function is altered, such as in epilepsy. Here, we evaluated the seizure susceptibility of mice transplanted with MGE-derived cells in the maximum electroconvulsive shock (MES) model and we review some data from different studies using GABAergic precursor or GABA-releasing cell grafts in animal models of seizure and epilepsy.

Frequency and cause of disagreements in imaging diagnosis in children with ventriculomegaly diagnosed prenatally

To assess the frequency and cause of variability in diagnosis on cranial sonography and magnetic resonance imaging (MRI) in children referred following prenatal diagnosis of ventriculomegaly. Between 19 September 2003 and 16 March 2007, 119 infants with ultrasound and/or MRI studies performed within 13 months (median, 6 days) after birth, following prenatal referral for ventriculomegaly, were studied prospectively. There were 97 infants with ultrasound results and 53 with MRI, including 31 with both. Three sonologists and three pediatric neuroradiologists interpreted the postnatal ultrasound and MRI findings, blinded to prenatal diagnosis, and a final consensus diagnosis or group of diagnoses was obtained. Ventricular sizes as well as types of and reasons for any disagreement in diagnosis were recorded. Disagreements on a per patient basis were categorized as being major when they crossed diagnostic categories and had the potential to change patient counseling. Postnatal and prenatal diagnoses were compared. There was prospective agreement on 42/97 (43%) ultrasound and on 9/53 (17%) MRI readings. Prospective consensus was more likely when the number of central nervous system (CNS) anomalies was lower (P < 0.001 and P = 0.002 for ultrasound and MRI, respectively). In 24/55 (44%) ultrasound and 11/44 (25%) MRI examinations with disagreement in diagnosis, there was disagreement concerning the presence of ventriculomegaly. In 22/97 (23%) ultrasound studies and 22/53 (42%) MRI studies the disagreements were potentially important. Reasons for discrepancies in the reporting of major findings included errors of observation as well as modality differences in depiction of abnormalities. In comparing prenatal with postnatal diagnoses, there were 11/97 (11%) ultrasound and 27/53 (51%) MRI examinations with newly detected major findings, the most common being migrational abnormalities, callosal dysgenesis/destruction and interval development of hemorrhage. Variability in postnatal CNS diagnosis is common after a prenatal diagnosis of ventriculomegaly. This is due in part to a lack of standardization in the definition of postnatal ventriculomegaly.

Glial progenitors in the brainstem give rise to malignant gliomas by platelet‐derived growth factor stimulation

Glial progenitors in the white matter and the subventricular zone are the major population of cycling cells in the postnatal central nervous system, and thought to be candidates for glioma-initiating cells. However, less is known about the dividing cell populations in the brainstem than those in the cerebrum, leading to the lag of basic understanding of brainstem gliomas. We herein demonstrate much fewer cycling glial progenitors exist in the brainstem than in the cerebrum. We also show that infecting brainstem glial progenitors with PDGFB-green fluorescent protein (GFP)-expressing retrovirus induced tumors that closely resembled human malignant gliomas. Of note, brainstem tumors grew more slowly than cerebral tumors induced by the same retrovirus, and >80% tumor cells in the brainstem consisted of GFP-positive, infected progenitors while GFP-positive cells in the cerebral tumors were <20%. These indicate that cerebral tumors progressed rapidly by recruiting resident progenitors via paracrine mechanism whereas brainstem tumors grew more slowly by clonal expansion of the infected population. The cerebral and brainstem glial progenitors similarly showed reversible dedifferentiation upon PDGF stimulation in vitro and did not show the intrinsic difference in terms of the responsiveness to PDGF. We therefore suggest that slower, monoclonal progression pattern of the brainstem tumors is at least partly due to the environmental factors including the cell density of the glial progenitors. Together, these findings are the first implications regarding the cell-of-origin and the gliomagenesis in the brainstem.

Secreted semaphorins control spine distribution and morphogenesis in the postnatal CNS

The majority of excitatory synapses in the mammalian CNS are formed on dendritic spines1, and spine morphology and distribution are critical for synaptic transmission2–6, synaptic integration and plasticity7. Here, we show that a secreted semaphorin, Sema3F, is a negative regulator of spine development and synaptic structure. Mice with null mutations in genes encoding Sema3F, and its holoreceptor components neuropilin-2 (Npn-2) and plexinA3 (PlexA3), exhibit increased dentate gyrus (DG) granule cell (GC) and cortical layer V pyramidal neuron spine number and size, and also aberrant spine distribution. Moreover, Sema3F promotes loss of spines and excitatory synapses in dissociated neurons in vitro, and in Npn-2−/− brain slices cortical layer V and DG GCs exhibit increased mEPSC frequency. In contrast, a distinct Sema3A–Npn-1/PlexA4 signaling cascade controls basal dendritic arborization in layer V cortical neurons but does not influence spine morphogenesis or distribution. These disparate effects of secreted semaphorins are reflected in the restricted dendritic localization of Npn-2 to apical dendrites and of Npn-1 to all dendrites of cortical pyramidal neurons. Therefore, Sema3F signaling controls spine distribution along select dendritic processes, and distinct secreted semaphorin signaling events orchestrate CNS connectivity through the differential control of spine morphogenesis, synapse formation, and the elaboration of dendritic morphology.

Co‐localization of Nkx6.2 and Nkx2.2 homeodomain proteins in differentiated myelinating oligodendrocytes

Recent studies have suggested that Nkx6.2/Gtx and Nkx2.2 homeodomain transcription factors are involved in the regulation of oligodendrocyte maturation and/or myelination which occur predominantly in postnatal stages. However, their cellular specificity in postnatal central nervous system has not been characterized and their dynamic expressional relationship during oligodendrocyte lineage progression has not been determined. Here we report that both Nkx2.2 and Nkx6.2 are selectively expressed in Olig2+ cells of oligodendrocyte lineage in postnatal spinal cords. Although Nkx6.2 is specifically expressed in the APC+ mature oligodendrocytes, Nkx2.2 is initially expressed in differentiating oligodendrocyte precursor cells (OPCs) but quickly down-regulated as OPCs undergo terminal differentiation. Intriguingly, Nkx2.2 expression is up-regulated in mature myelinating oligodendrocytes at later stages. The co-expression of Nkx2.2 and Nkx6.2 transcription factors in myelinating oligodendrocytes suggests their functional interactions in the regulation of myelin sheath formation and/or maintenance.

Engineering of Dominant Active Basic Helix-Loop-Helix Proteins That Are Resistant to Negative Regulation by Postnatal Central Nervous System Antineurogenic Cues

Neural precursor cells (NPCs) are present in most regions of the adult central nervous system (CNS). Using NPCs in a therapeutical perspective, that is, to regenerate CNS tissue after injury or in neurodegenerative diseases, will require the efficient manipulation of their fate. Proneural gene overexpression in NPCs represents a promising strategy to promote neuronal differentiation. The activity of the proneural proteins is, however, context-dependent and can be inhibited/modulated by binding with other bHLH (basic helix-loop-helix) or HLH transcription factors. In this study, we show that the two proneural proteins, Ngn2 and Mash1, are differentially sensitive to negative regulation by gliogenic factors or a gliogenic substrate (i.e., postnatal spinal cord slices). Coexpressing E-proteins with proneural proteins was efficient to rescue proneural proteins neurogenic activity, suggesting a central role for E-protein sequestration in mediating postnatal CNS gliogenic inhibition. Tethering of proneural proteins with E47 further insulated Mash1 from negative environmental influences whereas this strategy was not successful with Ngn2, suggesting that mechanisms of inhibition differ in between these two proneural proteins. Our results demonstrate that a better understanding of proneural protein modulation by environmental cues is a prerequisite to develop innovative approaches that will permit the manipulation of the fate of NPCs in the adult CNS after trauma or disease.

Functional α7‐containing nicotinic receptors of NG2‐expressing cells in the hippocampus

In the postnatal central nervous system, glial cells expressing the chondroitin sulfate proteoglycan NG2 (NG2-cells) constitute a cell population exhibiting several properties of oligodendrocyte precursors such as the ability to proliferate. One particular feature of NG2-cells is that they express several glutamatergic and GABAergic ionotropic receptors activated by synaptic neurotransmitter release. Here, we used patch-clamp recordings, immunostaining, calcium imaging, and intracellular labeling to test for the presence of ionotropic nicotinic acetylcholine receptors (nAChRs) in NG2-cells identified in acute hippocampal slices of mice. We demonstrated that these cells express functional nAChRs during the second postnatal week, i.e., the period in which they become the most abundant proliferative cell type of CA1 stratum radiatum. Pharmacological experiments showed that NG2-cells express alpha 7-containing nAChRs. In particular, the powerful positive allosteric modulator of these receptors PNU-120596 induced a 20-fold increase of agonist-induced currents and revealed rises in intracellular calcium concentration upon agonist applications. In addition, nanomolar concentrations of nicotine, which did not induce any response in these cells, largely desensitized nAChR-mediated currents. These data indicate that the functional expression of Ca(2+)-permeable alpha 7-containing nAChRs in hippocampal slices is not restricted to neurons and that the receptors of NG2-cells can be desensitized by low concentrations of nicotine.

50 Years Ago in The Journal of Pediatrics: Comments on current literature: congenital damage to the central nervous system as a result of intrauterine infection

Blattner RJ. J Pediatr 1958;52:620-6 As little as 50 years ago, the importance of intrauterine infection as a cause of damage to the fetal central nervous system (CNS) was not widely appreciated. Autopsy studies on large series of patients identified only syphilis as a relatively common etiology of intrauterine and early postnatal CNS damage. In 1957, Edith Potter described the clinical pathological correlation of intrauterine cytomegalic inclusion body disease (CMV) due to placental transfer of viruses. It was recognized that human “salivary gland virus,” rarely responsible for overt illness in mother, could cause severe or fatal disease when transferred placentally to the fetus. Examination of the urinary sediment for inclusion bodies was the only available diagnostic procedure. We now realize that intrauterine infections, both systemic and involving the CNS, are a frequent and important cause of morbidity and mortality in the neonatal period. As many as 2% of fetuses are infected in utero by viral, bacterial, fungal, or protozoal agents. The acronym TORCH is widely used, although it has recently been maligned for its simplicity and lack of specificity. Congenital CMV infection is the most common intrauterine infection in developed countries, affecting 0.2% to 2.2% live neonates. Contemporary obstetrics involves first and second trimester ultrasound examinations, which can reveal abnormalities that suggest possible intrauterine infections, including intracranial calcifications, hydrocephalus, hyperechoic bowel, and intrauterine growth restriction. There is great variability in the clinical specificity and yield of algorithms used to evaluate these patients. Thankfully, a variety of microbiological and molecular tools with a high degree of diagnostic specificity are now available. Potter's report indicated that transplacental fetal infection often went undiagnosed during pregnancy because the mother was asymptomatic or had nonspecific signs and symptoms at the time of acute infection. We now appreciate not only the frequency of these important infections but also the importance of the stage of gestation at which infection occurs and the risk of adverse outcome. Nowadays, the obstetric standard of care is to screen all pregnant women for rubella, syphilis, hepatitis B, group B streptococcus, Chlamydia, and gonorrhea (with some states also screening for HIV), the most common and preventable perinatally acquired infections. Examination of the placenta also is recommended when infection is being considered as a causal or contributing factor to preterm delivery, fetal tachycardia, maternal signs of chorioamnionitis, neonatal intensive care unit admission, stillbirth, fetal birth defects, or abnormalities in intrauterine growth.

Expression of the transcription factor GATA3 in the postnatal mouse central nervous system

GATA binding protein 3 (GATA3) is an important regulator of central nervous system (CNS) development, but its expression pattern in the postnatal CNS has not been studied. In the present study, we examined the distribution of GATA3 mRNA in the mouse CNS at different postnatal stages by in situ hybridization. During the first 2 weeks of postnatal development, numerous GATA3-expressing cells were found in the intergeniculate leaf, ventral lateral geniculate nucleus, pretectal nucleus, nucleus of the posterior commissure, superior colliculus, inferior colliculus, periaqueductal grey, substantia nigra and raphe nuclei. Few notable changes in the profile of GATA3 expression occurred over this time period. As postnatal development progressed, however, GATA3 expression weakened, and was maintained in only a few regions of the adult CNS. Throughout the brain, we found that GATA3-expressing cells were NeuN-positive, and no colocalization with glial fibrillary acidic protein (GFAP) was observed. In the substantia nigra, GATA3 was exclusively expressed in cells of the reticulate part and some of which were found to be GABAergic. This study presents a comprehensive overview of GATA3 expression in the CNS throughout postnatal life, and the dynamics that we observed provide insights for further investigations of the roles of GATA3 in postnatal development and the maintenance of the mature CNS.

Essential role of B-Raf in oligodendrocyte maturation and myelination during postnatal central nervous system development

Mutations in the extracellular signal-regulated kinase (ERK) pathway, particularly in the mitogen-activated protein kinase/ERK kinase (MEK) activator B-Raf, are associated with human tumorigenesis and genetic disorders. Hence, B-Raf is a prime target for molecule-based therapies, and understanding its essential biological functions is crucial for their success. B-Raf is expressed preferentially in cells of neuronal origin. Here, we show that in mice, conditional ablation of B-Raf in neuronal precursors leads to severe dysmyelination, defective oligodendrocyte differentiation, and reduced ERK activation in brain. Both B-Raf ablation and chemical inhibition of MEK impair oligodendrocyte differentiation in vitro. In glial cell cultures, we find B-Raf in a complex with MEK, Raf-1, and kinase suppressor of Ras. In B-Raf–deficient cells, more Raf-1 is recruited to MEK, yet MEK/ERK phosphorylation is impaired. These data define B-Raf as the rate-limiting MEK/ERK activator in oligodendrocyte differentiation and myelination and have implications for the design and use of Raf inhibitors.

Risk factors and clinical profiles in Turkish children with cerebral palsy: analysis of 625 cases

The aim of the study was to investigate risk factors, clinical profiles and gross motor function levels of Turkish children with cerebral palsy (CP). A total of 625 consecutive children with CP, who were rehabilitated in the pediatrics rehabilitation clinic between 2000 and 2004 years, were included. Factors causing CP were investigated by interviewing the families and by scanning medical files. Risk factors were recorded as consanguineous marriage, maternal disorder, preterm birth, birth asphyxia, low birth weight, multiple pregnancy, neonatal convulsion, kernicterus, postnatal central nervous system infection and brain injury. Swedish classification was followed in CP typing. Of 625 children with CP, 370 (59.2%) were males and 255 (40.8%) were females, with ages ranging between 2 and 13 years (the mean age was 5.11+/-2.19 years). It was determined that 47.8% of the cases were spastic diplegic CP, 27.7% were spastic tetraplegic CP, 12.8% spastic hemiplegic CP and 11.7% were other types (ataxic, dyskinetic and mixed CP types). The most frequently encountered risk factors were low birth weight (45.1%), preterm birth (40.5%), birth asphyxia (34.6%) and consanguineous marriage (23.8%). Low birth weight, preterm birth, birth asphyxia and consanguineous marriage were top-ranked risk factors that were determined in Turkish children with CP. Compared with other countries, consanguineous marriage is still an important problem in Turkey.

Amnionless (AMN) mutations in Imerslund–Gräsbeck syndrome may be associated with disturbed vitamin B12 transport into the CNS

Familial selective vitamin B12 (cobalamin, Cbl) malabsorption (Imerslund-Gräsbeck syndrome, IGS, OMIM 261100) is a group of autosomal recessive disorders characterized by selective malabsorption of Cbl from the terminal ileum in the presence of normal histology. Mutations in the amnionless (AMN) and cubilin (CUBN) genes are known to be causes of IGS. Their gene products combine to form a receptor complex (cubam), which is instrumental in the binding and transport of Cbl in the gut. As opposed to Cbl transport in the terminal ileum, normal transport of Cbl into the CNS is poorly understood and little is known regarding its molecular basis. Studies in adults with neuropsychiatric disease have suggested the presence of an active transport mechanism into the central nervous system constituting a blood-brain barrier (BBB) for Cbl. A child with IGS, compound heterozygous for a missense and a nonsense mutation in the amnionless (AMN) protein gene, was noted to have a high daily cobalamin (Cbl) requirement for neuropsychiatric, but not for systemic metabolic and haematological, remission. Measurements of CSF Cbl revealed evidence that the transport of Cbl into the central nervous system was impaired, and a standard Schilling test was consistent with a dose response of cobalamin transport across the terminal ileum. Amnionless protein is known to be expressed in the fetal and postnatal central nervous system, and is known to be involved in Cbl transport in other tissues such as kidney as well as the gut. It is possible that an active Cbl transport mechanism at the BBB exists, and that the amnionless (AMN) protein may be part of this mechanism, as it is in cobalamin transport in the terminal ileum.

NG2 cells generate both oligodendrocytes and gray matter astrocytes

NG2 glia constitute a fourth major glial cell type in the mammalian central nervous system (CNS) that is distinct from other cell types. Although circumstantial evidence suggests that some NG2 glia differentiate into oligodendrocytes, their in vivo fate has not been directly examined. We have used the bacterial artificial chromosome (BAC) modification technique to generate transgenic mice that express DsRed or Cre specifically in NG2-expressing (NG2+) cells. In NG2DsRedBAC transgenic mice, DsRed was expressed specifically in NG2+ cells throughout the postnatal CNS. When the differentiation potential of NG2+ cells in vitro was examined using DsRed+NG2+ cells purified from perinatal transgenic brains, the majority of the cells either remained as NG2+ cells or differentiated into oligodendrocytes. In addition, DsRed+NG2+ cells also differentiated into astrocytes. The in vivo fate of NG2 glia was examined in mice that were double transgenic for NG2creBAC and the Cre reporter Z/EG. In the double transgenic mice, the Cre reporter EGFP was detected in myelinating oligodendrocytes and in a subpopulation of protoplasmic astrocytes in the gray matter of ventrolateral forebrain but not in fibrous astrocytes of white matter. These observations suggest that NG2+ cells are precursors of oligodendrocytes and some protoplasmic astrocytes in gray matter.