The functions of the actin nucleator Cobl in cellular morphogenesis critically depend on syndapin I

Abstract

Spatial control of cortical actin nucleation is indispensable for proper establishment and plasticity of cell morphology. Cobl is a novel WH2 domain-based actin nucleator. The cellular coordination of Cobl's nucleation activity, however, has remained elusive. Here, we reveal that Cobl's cellular functions are dependent on syndapin. Cobl/syndapin complexes form in vivo, as demonstrated by colocalization, coimmunoprecipitation and subcellular recruitment studies. In vitro reconstitutions and subcellular fractionations demonstrate that, via its lipid-binding Fer/CIP4 Homology (FCH)-Bin/Amphiphysin/Rvs (F-BAR) domain, syndapin recruits Cobl to membranes. Consistently, syndapin I RNAi impairs cortical localization of Cobl. Further functional studies in neurons show that Cobl and syndapin I work together in dendritic arbor development. Importantly, both proteins are crucial for dendritogenesis. Cobl-mediated functions in neuromorphogenesis critically rely on syndapin I and interestingly also on Arp3. Endogenous Cobl, syndapin I and the Arp2/3 complex activator and syndapin-binding partner N-WASP were present in one complex, as demonstrated by coimmunoprecipitations. Together, these data provide detailed insights into the molecular basis for Cobl-mediated functions and reveal that different actin nucleators are functionally intertwined by syndapin I during neuromorphogenesis.

Proteomic Analysis of Glycine Receptor β Subunit (GlyRβ)-interacting Proteins

“…8, center top). This local destabilization of synaptic F-actin might be further enhanced by additional effects of reduced SdpI levels on the actin nucleator cordon bleu (48). In conclusion, SdpI could contribute to synaptic GlyR anchoring by regulating receptor immobilization via the actin cytoskeleton.…”

“…Localization of SdpI in Spinal Cord Neurons-So far, SdpI has been studied pre-and postsynaptically at excitatory synapses in rat hippocampus (24,48,49) and presynaptically at the reticulospinal synapse in lamprey (19). Additionally, SdpI has been found in parvalbumin-positive inhibitory interneurons of the mouse brain (20).…”

“…Notably, the binding of SdpI to the GTPase dynamin depends on a similar motif, RRXPXXP, in which arginine residues provide positive charges for SdpI association (18). Recently, KXRAPXPP motifs have been implicated in SdpI binding to the actin nucleator cordon bleu (48). A comparison of all these SdpI-binding motifs reveals that dynamin and GlyR␤ and two of the three cordon bleu-binding sites all share the well known motif (R/K)XXPXXP involved in SH3 domain binding of polyproline type II helices (40).…”

Different functional modes of BAR domain proteins in formation and plasticity of mammalian postsynapses

“…SH3-domain-mediated interactions of syndapin I have been shown to play a pivotal role in the recruitment of cellular machineries involved in endocytic vesicle formation and actin nucleation (Schwintzer et al, 2011) to the plasma membrane. Furthermore, biochemical studies have demonstrated that, at least in the case of syndapin I, its SH3-domain-interaction partners can be incorporated into larger protein complexes that arise from self-association of syndapin F-BAR domains (Kessels and Qualmann, 2006;Schwintzer et al, 2011) (Fig. 3B).…”

FMRP regulates actin filament organization via the armadillo protein p0071

“…Morphometric measurements of transiently transfected hippocampal neurons were performed with ImageJ according to Schwintzer et al (2011). Transfected neurons identified by anti-MAP2 staining were imaged in systematic sweeps across the cover slips of repeated transfections with independent neuronal preparations.…”