Developing Mouse CNS Research Articles

Oligodendrocyte calcium signaling promotes actin-dependent myelin sheath extension

Myelin is essential for rapid nerve signaling and is increasingly found to play important roles in learning and in diverse diseases of the CNS. Morphological parameters of myelin such as sheath length are thought to precisely tune conduction velocity, but the mechanisms controlling sheath morphology are poorly understood. Local calcium signaling has been observed in nascent myelin sheaths and can be modulated by neuronal activity. However, the role of calcium signaling in sheath formation remains incompletely understood. Here, we use genetic tools to attenuate oligodendrocyte calcium signaling during myelination in the developing mouse CNS. Surprisingly, genetic calcium attenuation does not grossly affect the number of myelinated axons or myelin thickness. Instead, calcium attenuation causes myelination defects resulting in shorter, dysmorphic sheaths. Mechanistically, calcium attenuation reduces actin filaments in oligodendrocytes, and an intact actin cytoskeleton is necessary and sufficient to achieve accurate myelin morphology. Together, our work reveals a cellular mechanism required for accurate CNS myelin formation and may provide mechanistic insight into how oligodendrocytes respond to neuronal activity to sculpt and refine myelin sheaths.

Minor splicing snRNAs are enriched in the developing mouse CNS and are crucial for survival of differentiating retinal neurons.

In eukaryotes, gene expression requires splicing, which starts with the identification of exon-intron boundaries by the small, nuclear RNA (snRNAs) of the spliceosome, aided by associated proteins. In the mammalian genome, <1% of introns lack canonical exon-intron boundary sequences and cannot be spliced by the canonical splicing machinery. These introns are spliced by the minor spliceosome, consisting of unique snRNAs (U11, U12, U4atac, and U6atac). The importance of the minor spliceosome is underscored by the disease microcephalic osteodysplastic primordial dwarfism type 1 (MOPD1), which is caused by mutation in U4atac. Thus, it is important to understand the expression and function of the minor spliceosome and its targets in mammalian development, for which we used the mouse as our model. Here, we report enrichment of the minor snRNAs in the developing head/central nervous system (CNS) between E9.5 and E12.5, along with enrichment of these snRNAs in differentiating retinal neurons. Moreover, dynamic expression kinetics of minor intron-containing genes (MIGs) was observed across retinal development. DAVID analysis of MIGs that were cotranscriptionally upregulated embryonically revealed enrichment for RNA metabolism and cell cycle regulation. In contrast, MIGs that were cotranscriptionally upregulated postnatally revealed enrichment for protein localization/transport, vesicle-mediated transport, and calcium transport. Finally, we used U12 morpholino to inactivate the minor spliceosome in the postnatal retina, which resulted in apoptosis of differentiating retinal neurons. Taken together, our data suggest that the minor spliceosome may have distinct functions in embryonic versus postnatal development. Importantly, we show that the minor spliceosome is crucial for the survival of terminally differentiating retinal neurons.

BioMEA™: A versatile high-density 3D microelectrode array system using integrated electronics

Microelectrode arrays (MEAs) offer a powerful tool to both record activity and deliver electrical microstimulations to neural networks either in vitro or in vivo. Microelectronics microfabrication technologies now allow building high-density MEAs containing several hundreds of microelectrodes. However, dense arrays of 3D micro-needle electrodes, providing closer contact with the neural tissue than planar electrodes, are not achievable using conventional isotropic etching processes. Moreover, increasing the number of electrodes using conventional electronics is difficult to achieve into compact devices addressing all channels independently for simultaneous recording and stimulation. Here, we present a full modular and versatile 256-channel MEA system based on integrated electronics. First, transparent high-density arrays of 3D-shaped microelectrodes were realized by deep reactive ion etching techniques of a silicon substrate reported on glass. This approach allowed achieving high electrode aspect ratios, and different shapes of tip electrodes. Next, we developed a dedicated analog 64-channel Application Specific Integrated Circuit (ASIC) including one amplification stage and one current generator per channel, and analog output multiplexing. A full modular system, called BIOMEA™, has been designed, allowing connecting different types of MEAs (64, 128, or 256 electrodes) to different numbers of ASICs for simultaneous recording and/or stimulation on all channels. Finally, this system has been validated experimentally by recording and electrically eliciting low-amplitude spontaneous rhythmic activity (both LFPs and spikes) in the developing mouse CNS. The availability of high-density MEA systems with integrated electronics will offer new possibilities for both in vitro and in vivo studies of large neural networks.

Voltage-sensitive dye analysis of spontaneous depolarization waves in the developing mouse CNS

Voltage-sensitive dye analysis of spontaneous depolarization waves in the developing mouse CNS

Increased large conductance calcium-activated potassium (BK) channel expression accompanied by STREX variant downregulation in the developing mouse CNS

BackgroundLarge conductance calcium- and voltage activated potassium (BK) channels are important determinants of neuronal excitability through effects on action potential duration, frequency and synaptic efficacy. The pore- forming subunits are encoded by a single gene, KCNMA1, which undergoes extensive alternative pre mRNA splicing. Different splice variants can confer distinct properties on BK channels. For example, insertion of the 58 amino acid stress-regulated exon (STREX) insert, that is conserved throughout vertebrate evolution, encodes channels with distinct calcium sensitivity and regulation by diverse signalling pathways compared to the insertless (ZERO) variant. Thus, expression of distinct splice variants may allow cells to differentially shape their electrical properties during development. However, whether differential splicing of BK channel variants occurs during development of the mammalian CNS has not been examined.ResultsUsing quantitative real-time polymerase chain reaction (RT-PCR) Taqman™ assays, we demonstrate that total BK channel transcripts are up regulated throughout the murine CNS during embryonic and postnatal development with regional variation in transcript levels. This upregulation is associated with a decrease in STREX variant mRNA expression and an upregulation in ZERO variant expression.ConclusionAs BK channel splice variants encode channels with distinct functional properties the switch in splicing from the STREX phenotype to ZERO phenotype during embryonic and postnatal CNS development may provide a mechanism to allow BK channels to control distinct functions at different times of mammalian brain development.

Cystathionine β‐synthase, a key enzyme for homocysteine metabolism, is preferentially expressed in the radial glia/astrocyte lineage of developing mouse CNS

Cystathionine beta-synthase (CBS; EC 4.2.1.22) is a key enzyme in the generation of cysteine from methionine. A deficiency of CBS leads to homocystinuria, an inherited human disease characterized by mental retardation, seizures, psychiatric disturbances, skeletal abnormalities, and vascular disorders; however, the underlying mechanisms remain largely unknown. Here, we show the regional and cellular distribution of CBS in the adult and developing mouse brain. In the adult mouse brain, CBS was expressed ubiquitously, but it is expressed most intensely in the cerebellar molecular layer and hippocampal dentate gyrus. Immunohistochemical analysis revealed that CBS is preferentially expressed in cerebellar Bergmann glia and in astrocytes throughout the brain. At early developmental stages, CBS was expressed in neuroepithelial cells in the ventricular zone, but its expression changed to radial glial cells and then to astrocytes during the late embryonic and neonatal periods. CBS was most highly expressed in juvenile brain, and a striking induction was observed in cultured astrocytes in response to EGF, TGF-alpha, cAMP, and dexamethasone. Moreover, CBS was significantly accumulated in reactive astrocytes in the hippocampus after kainic acid-induced seizures, and cerebellar morphological abnormalities were observed in CBS-deficient mice. Taken together, these results suggest that CBS plays a crucial role in the development and maintenance of the CNS and that radial glia/astrocyte dysfunction might be involved in the complex neuropathological features associated with abnormal homocysteine metabolism.

Expression of high affinity choline transporter during mouse development in vivo and its upregulation by NGF and BMP-4 in vitro

An important feature of cholinergic neurons is high-affinity choline transport, which allows them to reuse choline for the synthesis of ACh needed to support cholinergic neurotransmission. The choline transporter, designated CHT, was recently cloned. We applied RT/PCR to monitor the expression of CHT in the developing mouse CNS from embryonic day 14 (E14) to postnatal day 30 (P30). We found that CHT was expressed early in development, predominantly in the regions containing cholinergic neurons. In the spinal cord, CHT mRNA was present at close to adult levels at the earliest time point examined (E14) and showed almost no changes after birth. In the striatum and the septum, CHT mRNA increased steadily during embryonic stages and leveled off after birth. Surprisingly, CHT mRNA expression was also detected in other brain regions, notably in the cerebellum, where it peaked on E19, and then rapidly declined during postnatal development. CHT protein was detected by Western blotting as a band of apparent molecular weight of 70 kDa. The accumulation of this protein during development lagged behind mRNA accumulation in all tissues. We also examined the effects of NGF and BMP-4, the potent inducers of choline acetyltransferase and vesicular acetylcholine transporter genes, on CHT expression. Both factors increased CHT mRNA accumulation in primary septal cultures. The effect of NGF was dependent on the PI3K signaling, as it was abolished by the PI3K inhibitor LY294002. This result indicates that some of the signals regulating other cholinergic-specific genes also control CHT expression.

Novel transcription factor Satb2 interacts with matrix attachment region DNA elements in a tissue‐specific manner and demonstrates cell‐type‐dependent expression in the developing mouse CNS

Satb1 is a first cell-type-specific transcription factor of a novel type that functions as a regulator of the transcription of large chromatin domains. We identified a close homologue of Satb1, Satb2, in a cDNA subtraction screening in a search for genes controlling neural differentiation. Satb2 showed 61% amino-acid homology to Satb1. Satb2 and Satb1 expression was detected in different cell subpopulations of developing mouse CNS in a mutually exclusive manner. In the electrophoretic mobility shift assay we demonstrate that nuclear extracts from the embryonic day 18.5 mouse developing neocortex, in contrast to basal ganglia, contain a protein complex interacting with matrix attachment region DNA elements (MARs) with high affinity. Endogenous Satb2 protein is a part of this complex. In the developing neocortex Satb2 was detected largely in the superficial layers. In the developing spinal cord Satb2 expression marks a subpopulation of Lbx1-positive neurons dorsally and a subgroup of Isl1-positive neurons ventrally. In the Lbx1 mutants Satb2 expression is greatly reduced. We suggest that Satb2 may regulate differentiation of subsets of neurons at the level of higher order chromatin structure via binding to MARs.

Developmental Regulation of β1 Integrins during Angiogenesis in the Central Nervous System

We examined β1 integrin expression during angiogenesis in the developing mouse CNS. Maturation of blood vessels was accompanied by three main events: (1) marked upregulation of β1 integrin expression; (2) a switch in β1 integrin expression, from α4 and α5 at postnatal day 1 to α1 and α6 in the adult; and (3) downregulation of fibronectin and upregulation of laminin expression. Thus, blood vessel maturation was associated with a developmental switch, from fibronectin-mediated signaling early in angiogenesis, to laminin-mediated signaling at later stages. To investigate the potential role of α4 and α5 integrins in angiogenesis, we developed a novel approach to purify endothelial cells from the CNS by selective adhesion to fibronectin. BrdU incorporation showed that fibronectin induced more endothelial cell proliferation than laminin, and antibody-blocking studies revealed that fibronectin mediated its effect via both α4 and α5 integrins. This work provides the first evidence that there is a developmental switch in the use of β1 integrins during angiogenesis. Furthermore, it suggests that regulation of β1 integrin and ECM expression by endothelial cells are important factors influencing vascular development in the CNS.

Identification and localization of M-CoREST (1A13), a mouse homologue of the human transcriptional co-repressor CoREST, in the developing mouse CNS.

By means of subtractive and differential hybridization techniques we have identified a novel murine gene (1A13) the expression of which is developmentally regulated in the mouse brain. Comparison of the nucleotide and predicted protein sequence revealed closest relationship of 1A13 to human CoREST, a transcriptional co-repressor required for regulation of neural-specific gene expression. Thus, we will refer to 1A13 as M-CoREST. As shown by in situ hybridization and Northern blotting, expression of M-CoREST mRNA is abundant in neural tissue at early embryonic stages but declines significantly towards birth, coincident with the progression of CNS maturation.

ABSTRACT Cytokine regulation of neural stem cell fate in the developing mouse CNS

ABSTRACT Cytokine regulation of neural stem cell fate in the developing mouse CNS

Developmental expression of voltage-gated potassium channel β subunits

Expression of potassium channel beta subunits (Kvβ) was determined in the developing mouse CNS using an antiserum against an amino acid sequence present in the C-terminus of Kvβ1, Kvβ2, and Kvβ3. Using the anti-Kvβ antiserum, we determined that Kvβ expression is restricted to the spinal cord and dorsal root ganglia in the embryonic CNS. At birth, Kvβ expression is detected in brainstem and midbrain nuclei, but was not detected in the hippocampus, cerebellum or cerebral cortex. During the first postnatal week, Kvβ expression is present in hippocampal and cortical pyramidal cells and in cerebellar Purkinje cells. Expression of Kvβ subunits reaches adult levels by the third postnatal week in all of the brain regions examined. A rabbit antiserum directed against a unique peptide sequence in the N-terminus of the Kvβ1 protein demonstrates that this subunit displays a novel expression pattern in the developing mouse brain. Kvβ1 expression is high at birth in all brain regions examined and decreases with age. In contrast, Kvβ2 expression is low at birth and increases with age to reach adult levels by the third postnatal week. These findings support the notion that the differential regulation of distinct potassium channel beta subunits, in the developing mouse nervous system, may confer the functional diversity required to mediate both neuronal survival and maturation.

Expression of PACAP Receptor Splice Variant mRNAs in the Developing Mouse CNS

Expression of PACAP Receptor Splice Variant mRNAs in the Developing Mouse CNS

EMX2 protein in the developing mouse brain and olfactory area

The distribution of EMX2, the protein product of the homeobox gene Emx2, was analyzed in the developing mouse CNS by means of a polyclonal antibody we raised against it. The protein is present in the rostral brain, the olfactory area and a set of scattered cells lying between the nasal pits and the telencephalon. In the cortical neuroepithelium EMX2 is expressed all along the rostro-caudal axis in a graded distribution with a caudal-medial maximum and a rostral-lateral minimum. Anti-EMX2 immunoreactivity is also detectable in Cajal–Retzius cells as well as in apical dendrites of marginal neurons of the cortical plate. We also observe that the EMX2 and EMX1 homeoproteins display complementary expression patterns in olfactory bulbs and amygdaloid complex. Here, they demarcate different neuronal populations, involved in processing olfactory information coming from the vomero-nasal organ and from the main olfactory epithelium, respectively. EMX2 is also detectable in mesencephalic structures, such as the optic tectum and tegmentum. The graded distribution of EMX2 along antero-posterior and medial-lateral axes of the primitive cortex prefigures a role of this protein in the subdivision of the cortex in cytoarchitectonic regions and possibly functional areas, whereas its presence in Cajal–Retzius cells suggests a role in the process of cortical lamination.

Nkx2-9 is a novel homeobox transcription factor which demarcates ventral domains in the developing mouse CNS

Nkx homeobox transcription factors are expressed in diverse embryonic cells and presumably control cell-type specification and morphogenetic events. Nkx2-9 is a novel family member of NK2 genes which lacks the conserved TN-domain found in all hitherto known murine Nkx2 genes. The prominent expression of Nkx2-9 in ventral brain and neural tube structures defines a subset of neuronal cells along the entire neuraxis. During embryonic development, Nkx2-9-expressing cells shift from the presumptive floor plate into a more dorsolateral position of the neuroectoderm and later become limited to the ventricular zone. Nkx2-9 expression overlaps with that of Nkx2-2 but is generally broader. While initially Nkx2-9 is expressed in close proximity to sonic hedgehog, its expression domain clearly segregates from sonic hedgehog at later developmental stages. The dynamic expression pattern of Nkx2-9 in ventral domains of the CNS is consistent with a possible role in the specification of a distinct subset of neurons.

Polysialic acid synthase (ST8Sia II/STX) mRNA expression in the developing mouse central nervous system.

A comparative study was undertaken to correlate the immunohistochemical localization of polysialic acid (PSA) and the in situ localization of ST8Sia II mRNA. In situ hybridization of postnatal day 3 mouse brain showed high levels of ST8Sia II mRNA expression in the cerebral neocortex, striatum, hippocampus, subiculum, medial habenular nucleus, thalamus, pontine nuclei, and inferior colliculus; intermediate-level expression in the olfactory bulb, hypothalamus, superior colliculus, and cerebellum; and low-level expression in other regions. The distribution of ST8Sia II mRNA in the neocortex and cerebellum coincided with the immunohistochemical localization of PSA. During brain development, ST8Sia II mRNA started decreasing and had almost disappeared by postnatal day 14. Comparison between ST8Sia II and IV mRNA expression was also undertaken by northern blot analysis and competitive PCR analysis. During the late embryonic to early postnatal stages of the mouse CNS, the ST8Sia II mRNA showed abundant mRNA expression compared with the ST8Sia IV mRNA. Competitive PCR analysis of the adult mouse CNS showed weak expression of the two genes in the olfactory bulb, thalamus, hippocampus, and eyes. The regional and transient expression of ST8Sia II mRNA coincides with that of PSA, suggesting that ST8Sia II is closely involved in the biosynthesis and expression of PSA in the developing mouse CNS.

BaxDeficiency Prevents the Increased Cell Death of Immature Neurons inbcl-x-Deficient Mice

The intracellular balance between pro- and antiapoptotic members of the Bcl-2 gene family is thought to regulate cell death. Targeted disruption of bcl-x, a death repressing member, causes massive cell death of immature neurons in the developing mouse CNS, whereas targeted disruption of bax, a proapoptotic member, blocks the death of specific populations of sympathetic and motor neurons. In the present study, mice deficient in both Bcl-xL and Bax (bcl-x-/-/bax-/-) are used to examine the relative significance and potential interactions of Bcl-xL and Bax during early CNS development. bcl-x-/-/bax-/- mice demonstrate greatly reduced levels of apoptosis both in vivo and in vitro compared with the CNS of Bcl-xL-deficient mice, as assessed by histology and terminal deoxytransferase-mediated deoxyuridine triphosphate nick end-labeling. Bax-deficient mice, however, contain occasional apoptotic cells in the developing CNS, and cultures of bax-deficient telencephalic cells demonstrate similar levels of apoptosis as wild-type cultures. These results suggest that Bax critically interacts with Bcl-xL to regulate survival of immature neurons, but indicate that other cell death regulating proteins, in addition to Bcl-xL and Bax, also function during CNS development.

Changes in the mouse neuroepithelium associated with cadmium-induced neural tube defects.

The aim of this study was to investigate the teratogenic action of cadmium (Cd) on the developing mouse CNS. Pregnant mice were injected with 4 mg/kg CdCl2 on day 7, 8, 9, or 10 of gestation. These animals and saline injected controls were sacrificed either on the day before birth or at various times up to 48 hours after injection and the embryos examined grossly and histologically. Exencephaly occurred after Cd treatment on day 7 or 8 and its development was examined in day 8 embryos. Eight hours after Cd injection many cells of the closing neural plate contained dense-staining inclusions, thought to be autophagic vacuoles. After 24 hours this damage had almost disappeared, but the anterior neural folds, although looking histologically normal, were more open than in controls. Forty-eight hours after injection it was apparent that this part of the neural tube was not going to close and would result in exencephaly. Cd exposure on day 9 or 10 did not cause gross CNS defects such as exencephaly. On both days, twelve hours after Cd injection, similar dark-staining inclusions were seen in many cells throughout the CNS. After twenty-four hours there were variable amounts of cell death, resulting in some embryos in breakdown of parts of the wall of the neural tube. Forty-eight hours after treatment all inclusions and cellular debris had disappeared, indicating repair had taken place, but in some embryos, treated on day 9, severe lasting damage was seen as dorsal openings in the previously closed neural tube.