Sahoko Miyama

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.

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.

Developmental regulation of the effects of fibroblast growth factor-2 and 1-octanol on neuronogenesis: Implications for a hypothesis relating to mitogen–antimitogen opposition

Neocortical neurons arise from a pseudostratified ventricular epithelium (PVE) that lies within the ventricular zone (VZ) at the margins of the embryonic cerebral ventricles. We examined the effects of fibroblast growth factor‐2 (FGF‐2) and 1‐octanol on cell output behavior of the PVE in explants of the embryonic mouse cerebral wall. FGF‐2 is mitogenic and 1‐octanol antimitogenic in the PVE. Whereas all postmitotic cells migrate out of the VZ in vivo, in the explants some postmitotic cells remain within the VZ. We refer to these cells as the indeterminate or I fraction, because they neither exit from the VZ nor reenter S phase as part of the proliferative (P) fraction. They are considered to be either in an extremely prolonged G1 phase, unable to pass the G1/S transition, or in the G0 state. The I fate choice is modulated by both FGF‐2 and 1‐octanol. FGF‐2 decreased the I fraction and increased the P fraction. In contrast, 1‐octanol increased the I fraction and nearly eliminated the P fraction. The effects of FGF‐2 and 1‐octanol were developmentally regulated, in that they were observed in the developmentally advanced lateral region of the cerebral wall but not in the medial region.

Children with posterior reversible encephalopathy syndrome associated with atypical diffusion-weighted imaging and apparent diffusion coefficient

Posterior reversible encephalopathy syndrome (PRES) is a reversible, predominantly posterior, leukoencephalopathy associated with renal insufficiency, hypertension, or immunosuppressant drugs. We describe two children with PRES whose primary diagnoses were idiopathic nephrotic syndrome and lupus nephritis. Cranial magnetic resonance (MR) imaging at the onset of PRES showed strong hyperintense signals on diffusion-weighted imaging with restricted apparent diffusion coefficient values predominantly in the posterior region. Such findings have been rarely reported in children with PRES and initially suggested irreversible brain damage; however, both children fully recovered clinically as well as radiologically. Our findings suggest the limitations of cranial MR imaging for diagnosing PRES. Further experience with cranial MR imaging, including diffusion-weighted imaging with apparent diffusion coefficient mapping, is required to improve diagnostic accuracy and the ability to predict outcomes in patients with early-stage PRES. At present, initial imaging studies do not necessarily provide sufficient evidence for a firm diagnosis of PRES or the prediction of outcomes.

Regulation of Normal Proliferation in the Developing Cerebrum Potential Actions of Trophic Factors

We review here a computational model of neocortical histogenesis based upon experiments in the developing cerebral wall of the mouse. Though based upon experiments in mouse, commonalities of developmental history and structure of neocortex across mammalian species suggest that the principles which support this model will be generally applicable to neocortical evolution and development across species. In its scope the model spans the successive histogenetic events: cell proliferation, cell migration, and the positioning of cell somata in neocortical layers following migration. Neurons are produced in a pseudostratified epithelium (PVE) which lines the ventricular cavaties of the embryonic cerebrum. The parameters which determine the rate and total number of neurons produced in the PVE are (1) the size of the founder population, (2) the number of integer cell cycles executed by the founder population and its progeny in the course of the neuronogenetic interval, (3) the growth fraction, and (4) the fraction of cells which exits the cycle (Q fraction) with each integer cycle. There is a systematic relationship between the integer cycle of origin and the sequence of cell migration, position in the cortex, and the extent to which a set of postmigratory neurons will be diluted in the cortex by the combined effects of tissue growth and cell death. Variation across species in the number of integer cell cycles as a function of the rate of progression of Q may be expected to modulate profoundly the total numbers of neurons that are produced but not the relative proportions of neurons assigned to the major neocortical layers.

Hirschsprung disease as a yet undescribed phenotype in a patient with ARID1B mutation

Mutations in the BAF complex (mammalian SWI/SNF complex) are responsible for Coffin‐Siris syndrome, which is characterized by developmental delay, distinctive facial features, hirsutism, and hypoplasia/aplasia of the fifth finger/fingernails. Hirschsprung disease is characterized by defective stem cells in the enteric neural system, and the involvement of multiple signaling cascades has been implicated. So far, the roles of the BAF complex in the genesis of Hirschsprung disease have remained unknown. Here, we document a patient with coarse facial features, postnatal growth failure, developmental delay, epilepsy, and hypoplasia of the corpus callosum and cerebellum but without a hypoplastic fifth finger/fingernail. In addition, he had Hirschsprung disease. Exome sequencing with a gene set representing a total of 4,813 genes with known relationships to human diseases revealed a heterozygous frameshift mutation in ARID1B (c.5789delC p.Pro1930Leufs*44). The presence of a congenital cataract and Hirschsprung disease in the presently reported patient further expands the phenotypic spectrum of patients with ARID1B mutations and may suggest the potential role of the BAF complex in the pathogenesis of the enteric neural system. The present observation is in agreement with a recent study of Drosophila neuroblasts showing that the dysregulated BAF complex leads to an abnormal lineage progression of neural stem cell lineages and that Hirschsprung disease is caused by abnormal stem cell lineages in the peripheral neural tissues.

Epidemiology of Pediatric Convulsive Status Epilepticus With Fever in the Emergency Department A Cohort Study of 381 Consecutive Cases

Pediatric convulsive status epilepticus with fever is common in the emergency setting but leads to severe neurological sequelae in some patients. To explore the epidemiology of convulsive status epilepticus with fever, a retrospective cohort covering all convulsive status epilepticus cases with fever seen in the emergency department of a tertiary care children’s hospital were consecutively collected. Of the 381 consecutive cases gathered, 81.6% were due to prolonged febrile seizure, 6.6% to encephalopathy/encephalitis, 0.8% to meningitis, and 7.6% to epilepsy. In addition, seizures were significantly longer in encephalopathy/encephalitis cases than in prolonged febrile seizure cases (log rank test, P < .001). These results provide for the first time the pretest probability of final diagnoses in children with convulsive status epilepticus with fever in the emergency setting, and will help optimize the management of pediatric patients presenting to the emergency department with convulsive status epilepticus with fever.

Diagnostic use of computational retrotransposon detection: Successful definition of pathogenetic mechanism in a ciliopathy phenotype

Among more than 5,000 human monogenic disorders with known causative genes, transposable element insertion of a Long Interspersed Nuclear Element 1 (LINE1, L1) is known as the mechanistic basis in only 13 genetic conditions. Meckel–Gruber syndrome is a rare ciliopathy characterized by occipital encephalocele and cystic kidney disease. Here, we document a boy with occipital encephalocele, post‐axial polydactyly, and multicystic renal disease. A medical exome analysis detected a heterozygous frameshift mutation, c.4582_4583delCG p.(Arg1528Serfs*17) in CC2D2A in the maternally derived allele. The further use of a dedicated bioinformatics algorithm for detecting retrotransposon insertions led to the detection of an L1 insertion affecting exon 7 in the paternally derived allele. The complete sequencing and sequence homology analysis of the inserted L1 element showed that the L1 element was classified as L1HS (L1 human specific) and that the element had intact open reading frames in the two L1‐encoded proteins. This observation ranks Meckel–Gruber syndrome as only the 14th disorder to be caused by an L1 insertion among more than 5,000 known human genetic disorders. Although a transposable element detection algorithm is not included in the current best‐practice next‐generation sequencing analysis, the present observation illustrates the utility of such an algorithm, which would require modest computational time and resources. Whether the seemingly infrequent recognition of L1 insertion in the pathogenesis of human genetic diseases might simply reflect a lack of appropriate detection methods remains to be seen.