Age dependent forebrain structural changes in mice deficient in the autism associated gene Met tyrosine kinase.

The MET tyrosine kinase has been identified as a susceptibility gene in patients with autism spectrum disorders. MET is expressed in the forebrain during prenatal and postnatal development. After birth, MET participates in dendritic outgrowth and circuit formation. Alterations in neuronal development, particularly in the cerebral cortex, may contribute to the pathology of developmental disorders, including autism. Patients with autism can exhibit abnormal cortical volumes and head circumferences. We tested the hypothesis that impaired Met signaling during development alters forebrain structure. We have utilized a conditional mutant mouse line which expresses a kinase-dead Met restricted to the cerebral cortex and hippocampal structures. In these mice, we have used magnetic resonance imaging (MRI) to analyze the structure of the cerebral cortex and related structures across postnatal development. We found that the rostral cortex, caudal hippocampus, dorsal striatum, thalamus, and corpus callosum were all larger in adult, but not juvenile, mutant mice relative to control mice. The specificity of the changes suggests that aberrant expansion of the forebrain is consistent with continued axonal and dendritic growth, potentially leading to improper circuit formation and maintenance.