Cortical development

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Which derivative of the prosencephalon forms the rudiments of the cerebral cortex? When does the differentiation of the prosencephalon occur?: *telencephalon
*between embryonic weeks 3 and 8
Describe the growth pattern that results in the hemispheric structure of the cortex.: *cells on the midline growth plate divide less and show more apoptosis...this results in the fixation of the plate
*cells in the lateral portions proliferate rapidly
Name one chemical secreted by organizer tissue that in part directs patterning of the cortex.: *sonic hedgehog (SHH)
(*FGf8)
Describe the gross defect seen in holoprosencephaly. Deletions in what gene have been implicated as a cause of HPE?: *forebrain fails to separate; cortex is continuous as a single holosphere rather than two hemispheres
*SHH in mesencephalon
In what part of the developing cortex does cell proliferation occur?: Ventricular zone of proliferation, adjacent to the lumen of the brain.
What kinds of cells are produced when a neural precursor cell divides symmetrically? When it divides asymmetrically?: *symmetric division = 2 glial cells
*assymetric division = 1 neuron + 1 glial cell
What are the signs of microcephaly? What is the general defect?: *small cortex, MR
*failure to generate the appropriate number of neurons
What is ASPM? What do defects in APSM result in? How?: *abnormal spindle protein
*microcephaly
*interferes with the organization of spindle fibers in mitotic cells, causing them to arrest in M-phase
Mutations in the gene coding for B-catenin have caused what kinds of effects in lab animals? What is the mechanism?: *macrocephaly
*enlarged lateral ventricles and an expanded pool of neural precursors
When is neural cell fate atleast partially specified?: In the paraventricular zone when the neuron is born.
Underexpression of GABA neurons can be induced by a specific mutation - what is it?: Double mutations to D1x-1/2.
What is the difference between radial and tangential migration of neurons?: *radial migration: movement along a glial scaffolding system
*tangential migration: movement in a glial-independent manner
How are cortical layers laid out - inside-out or outside in?: Inside-out, with the deepest layers made first and the most superficial layers made last.
What are the 3 general stages in neuron migration?: 1.Recognition of route and onset of migration
2.Maintenence of migration over long distances
3.Termination of migration at the proper location
What is schizencephaly?: *defect in neural migration results in random distribution of neurons
*fistula between ventricle and outer surface of brain seen
What is the gross appearance of the bain in Type 1 lissencephaly? What causes this defect? What is the mechanism?: *smooth cortical surface with no sulci or gyri
*mutation in Lis-1 gene
*abnormal accumulation of microtubules
What is the appearance of periventricular hetertopia? What is the primary problem? What symptoms are seen?: *enlarged periventricular area
*failure of neurons to initiate migration
*seizures
What is the molecular problem in periventricular hetertopia?: Mutations in the gene coding for filamin-1 prevent f-actin filaments from binding together normally.
Is periventricular hetertopia seen more frequently in boys or girls?: It is not seen in boys. The mutation is on an X-linked gene and males are spontaneously aborted. Females survive because they are mosaic carriers.
What is the appearance of polymicrogyria?: Small gyri inside the cortex.
a-3 integrin is proposed to play what role in neural migration? What is the molecular defect seen in knockout animals?: *recognition of surroundings during migration
*disruption of f-actin dynamics at the leading edge
Reeler mouse mutants have neurons that show an inability to terminate migration at the appropriate location. What is the appearance of these animals' brains?: The laminar structure of the cortex is reversed with layer 6 most superficial and layer 1 most deep.
How is neural migration affected in Walker-Warburg syndrome? What anatomical anomalies are seen?: *neurons fail to terminate migration at the proper location and splay out through the pia mater into the subarachnoid space
*hydrocephaly, thinning of the cortex, aplasia of corpus callosum
What is the genetic defect thought to be the cause of Walker-Warburg syndrome?: A mutation in the gene coding for mannosyltransferase wich regulates the glycosylation of many proteins.
What are the 6 steps in normal cortical development?: 1.Pattern formation
2.Cell proliferation
3.Cell fate specification
4.Cell migration
5.Cell differentiation
6.Synapse and circuit formation
A failure to make the correct synaptic connections generally results in what?: Induction of apoptotic pathways.
What defect results in neurological separation of the two cortical hemispheres?: Agenesis of the corpus callosum.
What is tuberus sclerosis? What is a common symptom?: *groups of abnormally placed neurons (tubers) make abberent connections with a variety of effects
*epilepsy
Fragile X Syndrome results from a mutation in the FMR-1 gene. What are the roles of this gene in normal individuals? There are three.: 1.Influence the initial generation of a synapse
2.Regulate the generation of NT's and chemotactic factors at the synapse
3.Destroy RNA complexes
How does the mutation of FMR-1 seen in Fragile X affect transcription of the gene?: *increases the number of CCG repeats in the gene
*this induces methylation of the gene
*transcription is turned off
What structural anomalies are seen in Fragile X syndrome?: *increase in dendritic spine density
*excess of long, thin spines
ARFGEF2 codes for proteins normally involved in vesicular transport of membrane components. What 2 defects are seen when this gene is mutated? What protein is inadequately transported in these patients?: 1.periventricular hetertopia
2.microcephaly
*B-catenin
What are three general effects seen in FAS?: 1.Increased neuronal apoptosis
2.Sparsity of dendrites
3.Deficits in neuronal growth resulting in loss of brain surface morphology
Describe microdysgenesia of the cortex. In what genetic condition is it commonly seen?: *abnormal gyrations that protrude through to subcortical layers
*trisomy 21
T/F: The brains of autistic patients are commonly much smaller in volume than normal brains.: False: most autistic patients exhibit macrocephaly.
Mutations in the neuregulin-1 gene have been implicated in schizophrenia. What is the normal role of this gene?: Development of radial glial cells and expression of certain neurotransmitter receptors.
T/F: Cortical development continues into adulthood.: This is true.

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