This would argue that CSPα-Hsc70 complex directly participates in oligomerization of dynamin 1 by switching its conformation to one that facilitates self-assembly. It also suggests that CSPα is probably not functioning to protect dynamin 1 from degradation, and in fact we do not find that dynamin 1

is ubiquitinated (data not shown). The apparent decrease in dynamin 1 levels in CSPα KO synapses may be accounted for by a selective PD0332991 in vitro loss of dynamin 1 from the membrane synaptic fractions (Figures S2A and S2B), again consistent with a deficit in membrane-associated oligomerization. We also ruled out that dynamin 1 is aggregated in the CSPα KO (Figure S5D). To investigate whether deletion of CSPα leads to a partial loss of dynamin 1 function, we explored if the CSPα KO phenocopies any aspects of the dynamin 1 KO. Similar to the CSPα KO, deletion of dynamin 1 in mice leads to activity-dependent synaptic find more dysfunction and perinatal lethality after 2 weeks. At an ultrastructural level, CSPα KO synapses have fewer

synaptic vesicles (Figures 5G and 5H) like the dynamin 1 KO (Ferguson et al., 2007 and Hayashi et al., 2008). A decrement in synaptic vesicle number is found in many other endocytic mutants (Dickman et al., 2005) and is consistent with the hypothesis that the CSPα KO has endocytic deficits. In an accompanying paper in this issue of Neuron, Rozas et al. (2012) have directly measured synaptic vesicle recycling in CSPα KO motor neurons with synaptopHluorin imaging and show deficits in dynamin-dependent synaptic Org 27569 vesicle endocytosis, consistent with a loss of dynamin 1 function in the CSPα KO. The distinct interactions of the Hsc70-CSPα chaperone complex with SNAP-25 and dynamin 1 reveal that this chaperone has a dual mode of action and is a testament to the versatility of this chaperone complex. Synapse loss is a cardinal

feature of neurodegenerative diseases such as AD (Selkoe, 2002). Therefore, it was intriguing to determine if a decrement of CSPα-dependent synapse maintenance mechanism plays a role in neurodegenerative diseases. Such an involvement was hinted at by the interaction of CSPα with huntingtin (Miller et al., 2003) (Figure 1D). Hence, we tested the levels of CSPα and Hsc70 in age-matched human control and AD brains. Interestingly, protein levels of CSPα and Hsc70 were both decreased by approximately 40% in the frontal cortex of AD brains (Figure S6), suggesting a possible role in synaptic degeneration. Consistent with previously published results, synaptophysin levels were also decreased in AD brains compared to age-matched controls, and served as a positive control in this cohort (Masliah et al., 2001). In this study, we sought to understand presynaptic mechanisms of synapse maintenance.