mortality/aging
• fewer than expected double homozygotes are found at P21, the expected numbers are found at E12.5-E16.5 and at E18.5-P0
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nervous system
• reduced size and medial shift of fimbria in coronal sections
• mossy fiber axons are absent from the infrapyramidal blade of the dentate gyrus
• ectopic axon bundles of thalamic origin are found in adult and embryonic brains apparently directed towards the ectopic cell clusters
• at E16.5, fewer thalamocortical axon fibers are seen in the intermediate zone and fewer fibers leaving the intermediate zone to enter the internal capsule
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• at E14.5, E16.5, and E18.5 clusters of ectopic cells are seen on the neocortical surface often associated with streams of migrating cells directed towards the ectopic cluster
• however, at E12.5 no ectopic cells are seen in the preplate
• these ectopic cells appear to be radially migrating neuroepithelial cells
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• at E14.5 and E18.5, Cajal-Retzius cells are displaced by ectopic cells but no substantial loss of these cells is seen
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• agenesis of the corpus callosum is seen in all homozygotes at E18.5 and in adults
• Probst bundles are seen in many adult homozygotes
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• the infrapyramidal blade of the dentate gyrus is foreshortened, deflected towards the thalamus, and lacks mossy fiber axons
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• focal heterotopias are found layer 1 of the cortex, but not in the cerebellum or olfactory bulb
• penetrance of heterotopias is 100%
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• focal heterotopias are found in the frontal cortex
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• focal heterotopias are found in the parietal cortex
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• meningeal fibroblasts have reduced punctate laminin, lack fibrillar laminin at the cell periphery, and fewer but thicker F-actin fibers
• however, no menigeal fibrosis is seen
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• areas of the marginal zone containing ectopic cells have disrupted pial basement membranes with reduced and disrupted chondroitin sulfate proteoglycan and laminin staining
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growth/size/body
• viable double homozygotes are smaller than their littermates
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cellular
• reduced size and medial shift of fimbria in coronal sections
• mossy fiber axons are absent from the infrapyramidal blade of the dentate gyrus
• ectopic axon bundles of thalamic origin are found in adult and embryonic brains apparently directed towards the ectopic cell clusters
• at E16.5, fewer thalamocortical axon fibers are seen in the intermediate zone and fewer fibers leaving the intermediate zone to enter the internal capsule
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