Primary cellular meningeal defects cause neocortical dysplasia and dyslamination.
OBJECTIVE
Cortical malformations are important causes of neurological morbidity, but in many cases their etiology is poorly understood. Mice with Foxc1 mutations have cellular defects in meningeal development. We use hypomorphic and null alleles of Foxc1 to study the effect of meningeal defects on neocortical organization.


METHODS
Embryos with loss of Foxc1 activity were generated using the hypomorphic Foxc1(hith) allele and the null Foxc1(lacZ) allele. Immunohistologic analysis was used to assess cerebral basement membrane integrity, marginal zone heterotopia formation, neuronal overmigration, meningeal defects, and changes in basement membrane composition. Dysplasia severity was quantified using 2 measures.


RESULTS
Cortical dysplasia resembling cobblestone cortex, with basement membrane breakdown and lamination defects, is seen in Foxc1 mutants. As Foxc1 activity was reduced, abnormalities in basement membrane integrity, heterotopia formation, neuronal overmigration, and meningeal development appeared earlier in gestation and were more severe. Surprisingly, the basement membrane appeared intact at early stages of development in the face of severe deficits in meningeal development. Prominent defects in basement membrane integrity appeared as development proceeded. Molecular analysis of basement membrane laminin subunits demonstrated that loss of the meninges led to changes in basement membrane composition.


CONCLUSIONS
Cortical dysplasia can be caused by cellular defects in the meninges. The meninges are not required for basement membrane establishment but are needed for remodeling as the brain expands. Specific changes in basement membrane composition may contribute to subsequent breakdown. Our study raises the possibility that primary meningeal defects may cortical dysplasia in some cases.
Department of Neurology, Program in Neuroscience, Institute for Regenerative Medicine, San Francisco, San Francisco, CA 94158, USA.
Jonathan H
JH
Hecht
Julie A
JA
Siegenthaler
Katelin P
KP
Patterson
Samuel J
SJ
Pleasure
D000818:Animals; D001485:Basement Membrane / Q000378:metabolism / Q000473:pathology*; D002465:Cell Movement / Q000235:genetics; D004195:Disease Models, Animal; D004622:Embryo, Mammalian; D005260:Female; D051858:Forkhead Transcription Factors / Q000172:deficiency / Q000235:genetics; D018507:Gene Expression Regulation, Developmental / Q000235:genetics; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D007797:Laminin / Q000378:metabolism*; D054220:Malformations of Cortical Development / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D008578:Meninges / Q000002:abnormalities*; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation / Q000235:genetics; D009474:Neurons / Q000378:metabolism / Q000473:pathology; D011247:Pregnancy; D019718:Receptors, CXCR4 / Q000235:genetics; D012097:Repressor Proteins / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000378:metabolism
C511143:Bcl11b protein, mouse; C527276:CXCR4 protein, human; D051858:Forkhead Transcription Factors; C112890:Foxc1 protein, mouse; D007797:Laminin; D019718:Receptors, CXCR4; D012097:Repressor Proteins; D025521:Tumor Suppressor Proteins; C485184:enhanced green fluorescent protein; C102645:laminin alpha 2; D049452:Green Fluorescent Proteins