The Timothy Syndrome Mutation In Cav1.2 Causes Dendritic Retraction Through Calcium-independent Activation Of The Rhoa Pathway

Abstract

L-type voltage-gated calcium channels (LTCs) play a key role in neuronal development by activating signaling pathways that regulate neuronal gene expression and morphology. A point mutation in the LTC CaV1.2, which blocks voltage-dependent inactivation (VDI), causes autism in Timothy Syndrome (TS) patients. While it is known how VDI influences the current through LTCs, it is not known how alterations in VDI affect the signalling function of CaV1.2 in neurons and ultimately cause developmental defects that lead to autism. Here we show that CaV1.2 channels containing the TS mutation (TS-CaV1.2) cause dendrite retraction and reduced dendrite branching in cortical neurons in vitro and in vivo. Surprisingly, we found that TS-CaV1.2 causes dendritic retraction independently of Ca2+ influx through the channel suggesting that the voltage-dependent conformational changes associated with VDI play an important and unexpected role in CaV1.2 signaling. In addition, we found that TS-CaV1.2 causes dendrite retraction by activating the RhoA signalling pathway. We found that the small GTP-binding protein Gem with the channel beta subunit play a critical role in mediating the calcium-independent activation of RhoA by TS-CaV1.2. Our results provide new insight into how LTCs are coupled to cytoskeletal signaling pathways in neurons and shed light on the molecular mechanisms underlying the generation of TS and other Autism Spectrum Disorders.Supported by NIH RO1 NS48564-01 to RD