Analyses of the function of CAPS family proteins in vivo

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Ca2+-dependent activator protein for secretion 2 (CAPS2 or CADPS2) potently promotes the release of brain-derived neurotrophic factor (BDNF). A rare splicing form of CAPS2 with deletion of exon3 (dex3) was identified to be overrepresented in some patients with autism. Therefore, we generated Caps2-dex3 mice and verified a severe impairment in axonal Caps2-dex3 localization, contributing to a reduction in BDNF release from axons. In addition, circuit connectivity, measured by spine and interneuron density, was diminished globally. The collective effect of reduced axonal BDNF release during development was a striking and selective repertoire of deficits in social- and anxiety-related behaviors. Together, these findings represent the first mouse model of a molecular mechanism linking BDNF-mediated coordination of brain development to autism-related behaviors and patient genotype.We found that somal CAPS2 is associated with the Golgi membrane, and mediates binding and recruitment of the GDP-bound form of ARF4 and ARF5 (members of the membrane trafficking small GTPase family) to the Golgi membrane. CAPS2 knockdown and over-expression of CAPS2-binding-deficient ARF4/5 both induced accumulation of the DCV resident protein chromogranin A (ChgA) around the Golgi apparatus. CAPS2 knockout mice have dilated trans-Golgi structures when viewed by electron microscopy. These results for CAPS2 strongly support our idea that the CAPS family proteins exert dual roles in DCV trafficking, mediating trafficking at both the secretion site for exocytosis and at the Golgi complex for biogenesis.