Cobl-like promotes actin filament formation and dendritic branching using only a single WH2 domain.

Local actin filament formation powers the development of the signal-receiving arbor of neurons that underlies neuronal network formation. Yet, little is known about the molecules that drive these processes and may functionally connect them to the transient calcium pulses observed in restricted areas in the forming dendritic arbor. Here we demonstrate that Cordon-Bleu (Cobl)-like, an uncharacterized protein suggested to represent a very distantly related, evolutionary ancestor of the actin nucleator Cobl, despite having only a single G-actin-binding Wiskott-Aldrich syndrome protein Homology 2 (WH2) domain, massively promoted the formation of F-actin-rich membrane ruffles of COS-7 cells and of dendritic branches of neurons. Cobl-like hereby integrates WH2 domain functions with those of the F-actin-binding protein Abp1. Cobl-like-mediated dendritic branching is dependent on Abp1 as well as on Ca2+ /calmodulin (CaM) signaling and CaM association. Calcium signaling leads to a promotion of complex formation with Cobl-like's cofactor Abp1. Thus, Ca2+ /CaM control of actin dynamics seems to be a much more broadly used principle in cell biology than previously thought.