Functional interdependence of the actin regulators CAP1 and cofilin1 in control of dendritic spine morphology

Abstract

The vast majority of excitatory synapses are formed on small dendritic protrusions termed dendritic spines. Dendritic spines vary in size and density that are crucial determinants of excitatory synaptic transmission. Aberrations in spine morphogenesis can compromise brain function and have been associated with neuropsychiatric disorders. Actin filaments (F-actin) are the major structural component of dendritic spines and therefore actin-binding proteins (ABP) that control F-actin dis-/assembly moved into the focus as critical regulators of brain function. Studies of the past decade identified the ABP cofilin1 as a key regulator of spine morphology, synaptic transmission and behavior, and they emphasized the necessity for a tight control of cofilin1 to ensure proper brain function. Here, we report spine enrichment of cyclase-associated protein 1 (CAP1), a conserved multidomain protein with largely unknown physiological functions. Super-resolution microscopy and live cell imaging of CAP1-deficient hippocampal neurons revealed impaired synaptic F-actin organization and dynamics associated with alterations in spine morphology. Mechanistically, we found that CAP1 cooperates with cofilin1 in spines and that its helical folded domain is relevant for this interaction. Moreover, our data proved functional interdependence of CAP1 and cofilin1 in control of spine morphology. In summary, we identified CAP1 as a novel regulator of the postsynaptic actin cytoskeleton that is essential for synaptic cofilin1 activity.

Cyclase-associated protein 1 (CAP1) represses MRTF-SRF-dependent gene expression in the mouse cerebral cortex

“…Studies from us and others identified cofilin1 and ADF as key actin regulators in neurons (Rust, 2015a, b), whose inactivation shifted the actin equilibrium towards Factin (Rust et al, 2010;Flynn et al, 2012;Wolf et al, 2015). Further, we recently demonstrated an interaction of cofilin1 with both CAP2 and CAP1 in neurons (Pelucchi et al, 2020;Schneider et al, 2021b;Heinze et al, 2022). We therefore expected increased SRF activity in neurons lacking i) cofilin1, ii) cofilin1 and ADF, iii) CAP2 and/or iv) CAP1.…”

“…These data suggested a crucial role for CAP1, but not for CAP2 in regulating neuronal SRF activity. Since previous studies revealed a cooperation of cofilin1 and CAP1 in actin subunit dissociation and in neuron morphology (Kotila et al, 2019;Shekhar et al, 2019;Schneider et al, 2021b;Heinze et al, 2022), we tested whether compound inactivation of both ABP further increased SRF activity. Interestingly, Creexpressing Cfl1 flx/flx /CAP1 flx/flx neurons (Cfl1/CAP1-dKO) displayed an increase in SRF reporter activity very similar to CAP1-KO neurons (Fig.…”

“…pcDNA3.1-CAP1-eGFP was purchased from GenScript, where CDS of NM_007598.4 was cloned upstream of eGFP. mCherry-CAP1, MYC-CAP1 and corresponding constructs with point mutations have been described previously (Heinze et al, 2022).…”

“…Instead, SRF activity was strongly increased upon inactivation of cyclase-associated protein 1 (CAP1), but not of its homolog CAP2. CAP1 is an ABP with largely unknown physiological functions (Rust et al, 2020;Rust and Marcello, 2022), which has been implicated in neuronal actin regulation only recently (Schneider et al, 2021b;Heinze et al, 2022). Reporter assays in isolated neurons combined with confocal microscopy as well as pharmacological and genetic approaches revealed that CAP1 promotes cytosolic MRTF retention and represses MRTF-SRF-induced gene expression via an actin-dependent mechanism.…”