Mammalian Diaphanous (Dia)-related formins initiate the assembly of filamentous actin downstream of Rho GTPases to regulate cellular processes such as cytokinesis, cell polarity, cell motility and adhesion. In this work, we show that Neurochondrin (NC) is a novel Dial interacting protein. NC specifically binds to the formin homology 3 (FH3), but not to the FH1 or FH2 domain of Dial. Both proteins show a partial co-localization in dissociated primary rat hippocampal neurons. Ectopic expression of both proteins induced neurite outgrowth in Neuro2A cells. Using a series of deletion mutants of NC we could show that the first 100 amino acids were responsible for its effect on neurite outgrowth, whereas the C-terminal part of NC had no neurite outgrowth promoting activity. Moreover, co-expression of the C terminus of NC with Dia1 Delta DAD resulted in a dramatic reduction of Dial-induced neurite outgrowth. On the basis of actin fractionation assays, SRF-activity assays as well as microtubule stabilization assays, we could demonstrate that the C terminus of NC does not influence the actin polymerizing activity of Dial, indicating a more specific function of NC in the modulation of Dial activity. (c) 2008 Elsevier Inc. All rights reserved.