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Cdc42 is a signaling protein important for reorganization of actin cytoskeleton and morphogenesis of cells. However, the functional role of Cdc42 in synaptic plasticity and in behaviors such as learning and memory are not well understood. Here we report that postnatal forebrain deletion of Cdc42 leads to deficits in synaptic plasticity and in remote memory recall using conditional knockout of Cdc42. We found that deletion of Cdc42 impaired LTP in the Schaffer collateral synapses and postsynaptic structural plasticity of dendritic spines in CA1 pyramidal neurons in the hippocampus. Additionally, loss of Cdc42 did not affect memory acquisition, but instead significantly impaired remote memory recall. Together these results indicate that the postnatal functions of Cdc42 may be crucial for the synaptic plasticity in hippocampal neurons, which contribute to the capacity for remote memory recall.DOI: http://dx.doi.org/10.7554/eLife.02839.001View Full TextTo Top
Cdc42 is a signaling protein important for reorganization of actin cytoskeleton and morphogenesis of cells. However, the functional role of Cdc42 in synaptic plasticity and in behaviors such as learning and memory are not well understood. Here we report that postnatal forebrain deletion of Cdc42 leads to deficits in synaptic plasticity and in remote memory recall using conditional knockout of Cdc42. We found that deletion of Cdc42 impaired LTP in the Schaffer collateral synapses and postsynaptic structural plasticity of dendritic spines in CA1 pyramidal neurons in the hippocampus. Additionally, loss of Cdc42 did not affect memory acquisition, but instead significantly impaired remote memory recall. Together these results indicate that the postnatal functions of Cdc42 may be crucial for the synaptic plasticity in hippocampal neurons, which contribute to the capacity for remote memory recall.
DOI: http://dx.doi.org/10.7554/eLife.02839.001
Neurons communicate with one another at junctions called synapses, which are typically formed between the dendrite of one neuron and the axon terminus of another. The dendrites are protrusions coming out of the cell body that receive inputs from other cells; the axon is a cable-like structure that enables neurons to contact other cells. In excitatory neurons in part of the brain called the hippocampus, the dendrites are themselves covered in structures called spines, so most synapses are formed between an axon terminus (belonging to the presynaptic cell) and a dendritic spine (on the postsynaptic cell). The hippocampus is necessary for the formation of long-term memories.
The strength of a synapse can increase or decrease over time—a property that is called synaptic plasticity. Changes in the strength of synapses are thought to underlie learning and memory, and long-lasting changes in synaptic strength involve increases or decreases in the number and size of dendritic spines. Such changes are possible because spines have an internal skeleton that can be assembled and disassembled in a matter of minutes. This ‘remodeling’ process is regulated by a family of enzymes called small GTPases. One of these, known as Cdc42, has been shown to promote the formation and maintenance of spines in cell culture, but its role in synaptic plasticity, learning and memory remains unknown.
Now, Kim, Wang et al. have used genetically modified mice who have had Cdc42 deleted from excitatory neurons in their forebrain to examine the functions of this enzyme in living animals. These ‘knockout’ mice showed a small but statistically significant reduction in the number of dendritic spines in the hippocampus. They also showed smaller changes in spine volume and impaired long-term synaptic plasticity in the hippocampus.
When the mice performed long-term memory tests where they learnt to associate a specific set of visual cues with an impending electric shock, the knockout mice performed well for up to a few days. However, when tested again on the same task 45 days later, the knockout mice did not perform as well as normal mice. This is surprising, given the presumed role of long-term synaptic plasticity in learning and memory, and indicates that Cdc42 is required for ‘remote memory’, the form of memory lasting for many days. Similar results were obtained with another memory test using a water maze, where the animals have to remember the location of a hidden platform. Normal mice remember the location for more than 30 days. In contrast, the knockout mice could only remember the location for a few days.
As well as providing the first demonstration of the role of Cdc42 in synaptic plasticity in live animals, the work of Kim, Wang et al. has provided new insights into the functions of this enzyme in memory. Further work is required to determine how Cdc42 interacts with other proteins present at synapses.
DOI: http://dx.doi.org/10.7554/eLife.02839.002
