A giant ankyrin-B mechanism for neuro-diversity/divergence through stochastic ectopic axon projections

ANK2 is a high-confidence autism spectrum disorder (ASD) gene where affected individuals exhibit diverse symptoms with a wide range of IQ. We report a cellular mechanism resulting in stochastic brain connectivity that provides a rationale for both gain and loss of function due to ANK2 mutation. Deficiency of giant ankyrin-B (ankB), the neurospecific ANK2 mutation target, results in ectopic CNS axon tracts associated with increased axonal branching. We elucidate a mechanism limiting axon branching, whereby giant ankB is recruited by L1CAM to periodic axonal plasma membrane domains where it coordinates cortical microtubules and prevents microtubule stabilization of nascent axon branches. Heterozygous giant ankB mutant mice exhibit innate social deficits combined with normal/enhanced cognitive function. Thus, giant ankB-deficiency results in gain of aberrant structural connectivity with penetrant behavioral consequences that may contribute to both high and low-function ASD and other forms of neurodiversity/divergence.