Calcium/Calmodulin-dependent protein kinase IV (CaMKIV) is found predominantly in neuronal nuclei and has been implicated in synaptic plasticity and memory. CaMKIV is localized to subsets of cortical neurons both in vivo and in vitro. Further characterization of cell type specific expression of CaMKIV revealed that CaMKIV expressing neurons were non-GABAergic in vivo and in vitro. In addition, some of the CaMKIV expressing neurons co-localized in vivo and in vitro with ER81, an ETS family transcription factor found in layer V neurons. Interestingly, CaMKIV upregulation in cortex during postnatal development suggests that CaMKIV may be essential for developmental events, such as filopodia formation and synaptogenesis. To examine the role of CaMKIV, we analyzed the dendrite morphology of E18 rat cortical neurons that expressed CaMKIV and those that did not. Dendrite complexity, as measured by number of branch points, number of primary dendrites, and dendrite length was significantly greater in CaMKIV positive neurons at 8 DIV in basal conditions. In addition, the number and density of filopodia were greater in CaMKIV expressing neurons. To test if CaMKIV is sufficient to promote dendritic complexity and filopodia formation constitutively active (ca) and wild type (wt) CaMKIV was coexpressed with GFP in cortical neurons. Neurons that expressed CaMKIVwt and CaMKIVca showed potentiated increases in filopodia number and density as well as in dendrite complexity. Furthermore, knockdown of CaMKIV with siRNA showed that CaMKIV is necessary for filopodia formation and dendrite complexity. CaMKIV, in addition to mediating dendrite complexity and filopodia formation, plays a role in spine formation. Endogenous CaMKIV expressing neurons showed increased post-synaptic density-95 (PSD95) labeled spines. Similarly, neurons that expressed CaMKIVwt and CaMKIVca showed potentiated increase in PSD95 labeled spines. Finally, basal dendrites and the apical tuft of layer 5 pyramidal neurons from CaMKIV null mice showed significant decrease in protrusion and spine densities when compared to wild type mice. Taken together, these results indicate that CaMKIV promotes dendrite arborization, including dendrite complexity, filopodia and spine formation.

INDEX WORDS: CaMKIV, dendrite, arborization, filopodia, spines