Conditional knockout of PTEN in adult progenitor cells of the subgranular zone of the hippocampus results in a depletion of the stem cell pool and development of hypertrophied neurons with abnormal polarity.92 Furthermore, conditional deletions of PTEN to discrete neuronal subpopulations in mice result in abnormal dendrite and axonal growth.93 There is also Cell Cycle inhibitor genetic evidence for impaired signaling beyond the mTOR pathway. For example, Inhibitors,research,lifescience,medical CNVs on chromosome 16 that disrupt the MAPK3 gene encoding extracellular signal-related kinase 1 (ERK1) are associated with autism94,95 and pinpoint disruptions of Ras/Raf/ERK1/2 signaling as a possible contributor to autism.96 Upregulation of this pathway results in impaired

neuronal cell migration, neurogenesis, synapse formation, and dendritic spine development.97 Also, two of the recent sequencing studies already discussed implicate dual-specificity tyrosine- (Y) -phosphorylation regulated kinase 1 A (DYRK1A),28,30 a serine/threonine kinase involved in Down syndrome Inhibitors,research,lifescience,medical that regulates neuronal morphogenesis via Inhibitors,research,lifescience,medical cytoskeletal dynamics.98 Taken together, combined in vitro

and in vivo studies would suggest impairments in intracellular signaling could lead to alterations in neuronal morphology and synaptic connections. Therefore, the genetic evidence in this case highlights disruptions of activity-independent neurodevelopmental mechanisms as a contributing factor to autism, especially those of neurite outgrowth. Such deficits, in turn, could

mimic the effects of epigenetic perturbations despite functioning activity-dependent processes since faulty neuronal wiring could produce an ineffective Inhibitors,research,lifescience,medical neuronal foundation for intepreting external stimuli. Postsynaptic Inhibitors,research,lifescience,medical density and cytoskeletal mechanisms Scaffolding proteins provide multimeric protein-protein interaction domains that localize key synaptic proteins and signaling molecules to the postsynaptic terminals, enabling effective neurotransmission and synaptic plasticity necessary for normal cognitive development in the brain. From autism de novo CNV studies, some critical genes that have been identified such as SHANK299 and SHANK3.100 Many of these genes are also implicated in other neurodevelopmental disorders with potentially overlapping mechanisms such as schizophrenia.46 Disrupting the function of these scaffolding proteins directly impairs the synapse organization and stabilization, Tryptophan synthase and neurite outgrowth. These cellular and physiological consequences were confirmed in knockdown animal models of SHANK2, which had smaller dendritic spines and reduced AMPA receptor currents.99 Dendritic morphology is intimately correlated to synaptic transmission and processing, and SHANK2 demonstrates how dysfunction of structural organization can lead to the physiological autistic phenotype of imbalanced excitatory and inhibitory currents.