Doc2 supports spontaneous synaptic transmission by a Ca(2+)-independent mechanism
- Neuron. 2011 Apr 28;70(2):244-51. doi: 10.1016/j.neuron.2011.03.011.
- 1. Department of Molecular and Cellular Physiology, Stanford University, 265 Campus Drive, Stanford, CA 94305-5453, USA.
Two families of CA(2+)-binding proteins have been proposed as CA(2+) sensors for spontaneous release: synaptotagmins and Doc2s, with the intriguing possibility that Doc2s may represent high-affinity CA(2+) sensors that are activated by deletion of synaptotagmins, thereby accounting for the increased spontaneous release in synaptotagmin-deficient synapses. Here, we use an shRNA-dependent quadruple knockdown of all four CA(2+)-binding proteins of the Doc2 family to confirm that Doc2-deficient synapses exhibit a marked decrease in the frequency of spontaneous release events. Knockdown of Doc2s in synaptotagmin-1-deficient synapses, however, failed to reduce either the increased spontaneous release or the decreased evoked release of these synapses, suggesting that Doc2s do not constitute CA(2+) sensors for asynchronous release. Moreover, rescue experiments revealed that the decrease in spontaneous release induced by the Doc2 knockdown in wild-type synapses is fully reversed by mutant Doc2B lacking CA(2+)-binding sites. Thus, our data suggest that Doc2s are modulators of spontaneous synaptic transmission that act by a CA(2+)-independent mechanism.