Tomohide Goto

Sequence of Neuron Origin and Neocortical Laminar Fate: Relation to Cell Cycle of Origin in the Developing Murine Cerebral Wall

Neurons destined for each region of the neocortex are known to arise approximately in an “inside-to-outside” sequence from a pseudostratified ventricular epithelium (PVE). This sequence is initiated rostrolaterally and propagates caudomedially. Moreover, independently of location in the PVE, the neuronogenetic sequence in mouse is divisible into 11 cell cycles that occur over a 6 d period. Here we use a novel “birth hour” method that identifies small cohorts of neurons born during a single 2 hr period, i.e., 10–20% of a single cell cycle, which corresponds to ∼1.5% of the 6 d neuronogenetic period. This method shows that neurons arising with the same cycle of the 11 cycle sequence in mouse have common laminar fates even if they arise from widely separated positions on the PVE (neurons of fields 1 and 40) and therefore arise at different embryonic times. Even at this high level of temporal resolution, simultaneously arising cells occupy more than one cortical layer, and there is substantial overlap in the distributions of cells arising with successive cycles. We demonstrate additionally that the laminar representation of cells arising with a given cycle is little if at all modified over the early postnatal interval of histogenetic cell death. We infer from these findings that cell cycle is a neuronogenetic counting mechanism and that this counting mechanism is integral to subsequent processes that determine cortical laminar fate.

Dominant-Negative Mutations in α-II Spectrin Cause West Syndrome with Severe Cerebral Hypomyelination, Spastic Quadriplegia, and Developmental Delay

A de novo 9q33.3-q34.11 microdeletion involving STXBP1 has been found in one of four individuals (group A) with early-onset West syndrome, severe hypomyelination, poor visual attention, and developmental delay. Although haploinsufficiency of STXBP1 was involved in early infantile epileptic encephalopathy in a previous different cohort study (group B), no mutations of STXBP1 were found in two of the remaining three subjects of group A (one was unavailable). We assumed that another gene within the deletion might contribute to the phenotype of group A. SPTAN1 encoding alpha-II spectrin, which is essential for proper myelination in zebrafish, turned out to be deleted. In two subjects, an in-frame 3 bp deletion and a 6 bp duplication in SPTAN1 were found at the initial nucleation site of the alpha/beta spectrin heterodimer. SPTAN1 was further screened in six unrelated individuals with WS and hypomyelination, but no mutations were found. Recombinant mutant (mut) and wild-type (WT) alpha-II spectrin could assemble heterodimers with beta-II spectrin, but alpha-II (mut)/beta-II spectrin heterodimers were thermolabile compared with the alpha-II (WT)/beta-II heterodimers. Transient expression in mouse cortical neurons revealed aggregation of alpha-II (mut)/beta-II and alpha-II (mut)/beta-III spectrin heterodimers, which was also observed in lymphoblastoid cells from two subjects with in-frame mutations. Clustering of ankyrinG and voltage-gated sodium channels at axon initial segment (AIS) was disturbed in relation to the aggregates, together with an elevated action potential threshold. These findings suggest that pathological aggregation of alpha/beta spectrin heterodimers and abnormal AIS integrity resulting from SPTAN1 mutations were involved in pathogenesis of infantile epilepsy.

Small heat shock protein 27 mutation in a Japanese patient with distal hereditary motor neuropathy

AbstractHeat shock protein 27 (HSP27) belongs to a family of small heat shock proteins that play significant roles in the cellular stress response and are also involved in the control of protein-protein interactions as chaperons. Mutation in HSP27 has been identified as the cause of axonal Charcot-Marie-Tooth disease (CMT) and distal hereditary motor neuropathy (HMN). Heat shock protein 22 (HSP22) is a molecular counterpart of HSP27, and its mutation is another cause of distal HMN. We screened the mutation of HSP27 and HSP22 in 68 Japanese patients with axonal CMT or unclassified CMT and six Japanese patients with distal HMN. We detected a heterozygous P182S mutation of HSP27 in a patient with distal HMN, but we found no mutations in HSP22. Mutation in HSP27 may impair the formation of the stable neurofilament network that is indispensable for the maintenance of peripheral nerves.

δ-catenin is a nervous system-specific adherens junction protein which undergoes dynamic relocalization during development

δ‐catenin is a member of the Armadillo repeat family and component of the adherens junction discovered in a two‐hybrid assay as a bona fide interactor with presenilin‐1 (Zhou et al., [ 1997 ], NeuroReport 8:2085–2090), a protein which carries mutations that cause familial Alzheimers disease. The expression pattern of δ‐catenin was mapped between embryonic day 10 (E10) and adulthood by Northern blots, in situ hybridization and immunohistochemistry in the mouse. In development, δ‐catenin is dynamically regulated with respect to its site of expression. It is first expressed within proliferating neuronal progenitor cells of the neuroepithelium, becomes down‐regulated during neuronal migration, and is later reexpressed in the dendritic compartment of postmitotic neurons. In the mouse, δ‐catenin mRNA is expressed by E10, increases and peaks at postnatal day (P)7, with lower levels in adulthood. In the developing neocortex, δ‐catenin mRNA is strongly expressed in the proliferative ventricular zone and the developing cortical plate, yet is conspicuously less prominent in the intermediate zone, which contains migrating cortical neurons, δ‐catenin protein forms a honeycomb pattern in the neuroepithelium by labeling the cell periphery in a typical adherens junction pattern. By E18, δ‐catenin expression shifts primarily to nascent apical dendrites, a pattern that continues through adulthood. The dynamic relocalization of δ‐catenin expression during development, taken together with previously published data which described a role for δ‐catenin in cell motility (Lu et al., [ 1999 ] J. Cell. Biol. 144:519–532), suggests the hypothesis that δ‐catenin regulation is closely linked to neuronal migration and may play a role in the establishment of mature dendritic relationships in the neuropil. J. Comp. Neurol. 420:261–276, 2000.

Whole exome sequencing identifies KCNQ2 mutations in Ohtahara syndrome.

We thank Drs Jellinger and Attems for their interest in our study. In agreement with prior reports, we found that Parkinson disease (PD) pathology, including nigral neuronal loss and Lewy body pathology, is common in older adults without PD. Furthermore, we provide evidence that PD nigral pathology is related to parkinsonian motor signs in persons without a clinical diagnosis of PD. This contrasts with prior studies of incidental Lewy body disease, which found associations with subtle electrophysiologic changes but not with overt motor signs. Interestingly, in the current study, we also found that Alzheimer disease (AD) and cerebrovascular pathology showed independent associations with the severity of parkinsonian motor signs. As requested, the correlations among these common brain pathologies are included in the accompanying Table. It is interesting that Dr Attems and colleagues did not find an association of nigral pathology or cerebrovascular disease with parkinsonian signs among persons with AD. We and others have reported such associations. Overall, the findings in the current study have important public health implications. They suggest that mild parkinsonian signs, reported in up to 50% of older adults by age 85 years and associated with significant morbidity and mortality, may be caused by a range of pathologies including PD pathology, AD, and cerebrovascular pathologies. These data underscore the need for more sensitive clinical measures and biomarkers that can detect and differentiate the various neuropathologies underlying the development of parkinsonian signs in old age.

Altered patterns of neuron production in the p27KIP1 knockout mouse

The number and distribution of neurons in the murine neocortex are altered by loss of function of p27Kip1, a cyclin-dependent kinase inhibitor that regulates cell cycle progression at the G1 phase. We show that a temporary decline in the production of non-GABAergic projection neurons occurs in the dorsomedial neopallium of the p27Kip1 knockout mouse during the mid-term of neuronogenesis. It is followed by an augmentation of neuron production later in neuronogenesis leading to an increased production of projection neurons for the upper layers of the neocortex (layers II–IV). p27Kip1 is likely to play a critical role in cell internal regulatory mechanisms of proliferation/differentiation behavior of neural progenitor cells and may be directly involved in the control of neuron number during the period when non-GABAergic projection neurons for layers II–IV are being produced.

Carnitine palmitoyl transferase II polymorphism is associated with multiple syndromes of acute encephalopathy with various infectious diseases

The high incidence of acute encephalopathy in East Asia suggests the role of genetic factors in its pathogenesis. It has recently been reported that variations of the CPT II (carnitine palmitoyl transferase II) gene may be associated with fatal or severe cases of influenza-associated encephalopathy. In the present study, we examined the genotype of CPT II in cases of acute encephalopathy associated with various preceding infections. Twenty-nine Japanese patients with acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) or acute necrotizing encephalopathy (ANE) were studied. The frequency of F352C of CPT II exon 4 was significantly higher in patients than in controls. All patients who had allele C in F352C had allele I in V368I and allele M in M647V (CIM haplotype), which reportedly decreases CPT II activity to one third of that with FIM or FVM haplotype. The frequency of CIM haplotype was significantly different between patients and controls, but not between AESD and ANE. Our results revealed that having at least one CIM allele is a risk factor for the onset of acute encephalopathy, regardless of its antecedent infections.

ADORA2A polymorphism predisposes children to encephalopathy with febrile status epilepticus.

Objective: Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) is a childhood encephalopathy following severe febrile seizures, leaving neurologic sequelae in many patients. However, its pathogenesis remains unclear. In this study, we clarified that genetic variation in the adenosine A2A receptor (ADORA2A), whose activation is involved in excitotoxicity, may be a predisposing factor of AESD. Methods: We analyzed 4 ADORA2A single nucleotide polymorphisms in 85 patients with AESD. The mRNA expression in brain samples, mRNA and protein expression in lymphoblasts, as well as the production of cyclic adenosine monophosphate (cAMP) by lymphoblasts in response to adenosine were compared among ADORA2A diplotypes. Results: Four single nucleotide polymorphisms were completely linked, which resulted in 2 haplotypes, A and B. Haplotype A (C at rs2298383, T at rs5751876, deletion at rs35320474, and C at rs4822492) frequency in patients was significantly higher than in controls (p = 0.005). Homozygous haplotype A (AA diplotype) had a higher risk of developing AESD (odds ratio 2.32, 95% confidence interval 1.32–4.08; p = 0.003) via a recessive model. mRNA expression was significantly higher in AA than AB and BB diplotypes, both in the brain (p = 0.003 and 0.002, respectively) and lymphoblasts (p = 0.035 and 0.003, respectively). In lymphoblasts, ADORA2A protein expression (p = 0.024), as well as cellular cAMP production (p = 0.0006), was significantly higher in AA than BB diplotype. Conclusions: AA diplotype of ADORA2A is associated with AESD and may alter the intracellular adenosine/cAMP cascade, thereby promoting seizures and excitotoxic brain damage in patients.

CSF glutamate/GABA concentrations in pyridoxine-dependent seizures: etiology of pyridoxine-dependent seizures and the mechanisms of pyridoxine action in seizure control

Several lines of evidence suggest that the binding affinity of glutamate decarboxylase (GAD) to the active form of pyridoxine is low in cases of pyridoxine-dependent seizures (PDS) and that a quantitative imbalance between excitatory (i.e. glutamate) and inhibitory (i.e. gamma-aminobutyric acid, GABA) neurotransmitters could cause refractory seizures. However, inconsistent findings with GAD insufficiency have been reported in PDS. We report a case of PDS that is not accompanied by an elevated cerebrospinal fluid (CSF) glutamate concentration. Intravenous pyridoxine phosphate terminated generalized seizures which were otherwise refractory to conventional anti-epileptic medicines. No seizure occurred once oral pyridoxine (13.5 mg/kg per day) was started in combination with phenobarbital sodium (PB, 3.7 mg/kg per day). The electroencephalogram (EEG) normalized approximately 8 months after pyridoxine was started. The patient is gradually acquiring developmental milestones during the 15 months follow-up period. The CSF glutamate and GABA concentrations were determined on three separate occasions: (1) during status epilepticus; (2) during a seizure-free period with administration of pyridoxine and PB; and (3) 6 days after suspension of pyridoxine and PB and immediately before a convulsion. The CSF glutamate level was below the sensitivity of detection (<1.0 microM) on each of the three occasions; the CSF GABA level was within the normal range or moderately elevated. The CSF and serum concentrations of vitamin B6-related substances, before pyridoxine supplementation, were within the normal range. We suggest that (1) PDS is not a discrete disease of single etiology in that insufficient activation of GAD may not account for seizure susceptibility in all cases and (2) mechanism(s) of anti-convulsive effect of pyridoxine, at least in some cases, may be independent of GAD activation.

Proliferative Behavior of the Murine Cerebral Wall in Tissue Culture: Cell Cycle Kinetics and Checkpoints ☆

Cerebral wall from embryonic day 13 mice was cultured in a three-dimensional collagen matrix in defined, serum-free medium. The cerebral wall retained its normal architecture, including the radial glial fiber system, for up to 19 h in culture. The cell cycle was initially blocked at the S/G2/M and the G1/S phase transitions, resulting in a transient synchronization of the proliferative cells. The transient blockades correspond, we suggest, to the G2 checkpoint and G1 restriction point, adaptive mechanisms of normal proliferative cells. The blocks were relieved within a few hours of explantation with restoration of the interkinetic nuclear migration and flow of cells through the cycle phases. The duration of the reestablished cell cycle and those of G1, S, and combined G2-M phases were estimated to be 19.2, 6.3-8.3, 8.8, and 2.0-4.0 h, respectively. The leaving (Q) fraction of the cycle (0.64) was twice the in vivo value. Two-thirds of the Q fraction cells remained in the ventricular epithelium, resulting in a substantially low growth fraction of 0.73 compared with 1.0 in vivo. The embryonic murine cerebral explant, cultured in minimum essential medium, should be favorable for studies of cycle modulatory actions of cell external influences such as growth factors or neurotransmitters.