Ciboulot Regulates Actin Assembly during Drosophila Brain Metamorphosis

Abstract

A dynamic actin cytoskeleton is essential for the remodeling of cell shape during development, but the specific roles of many actin partners remain unclear. Here we characterize a novel actin binding protein, Ciboulot (Cib), which plays a major role in axonal growth during Drosophila brain metamorphosis. Loss of Cib function leads to axonal growth defects in the central brain, while overexpression of the gene during development leads to overgrown projections. The Cib protein displays strong sequence similarity to beta-thymosins but has biochemical properties like profilin: the Cib-actin complex participates in actin filament assembly exclusively at the barbed end, and Cib enhances actin-based motility in vitro. Genetic experiments show that Cib and the Drosophila profilin protein Chickadee (Chic) cooperate in central brain metamorphosis.

TetraThymosinβ Is Required for Actin Dynamics inCaenorhabditis elegansand Acts via Functionally Different Actin-binding Repeats

“…As outlined in detail in Materials and Methods, this SPR analysis demonstrates that at least three actin monomers can simultaneously interact with one tetraThymosin␤ molecule. This is clearly in contrast with conclusions made for the homologous protein ciboulot where a 1:1 stoichiometry is proposed (Boquet et al, 2000;Hertzog et al, 2002Hertzog et al, , 2004. The steepness of the slopes of the binding curves suggests that on and off rates are fast.…”

“…The actin-binding determinants of this module are clearly delineated: a hexapeptide motif ( 17 LKKTET 22 in thymosin␤4) and a hydrophobic cluster in a preceding ␣-helix (Vancompernolle et al, 1992;Van Troys et al, 1996b;Rossenu et al, 1997;Simenel et al, 2000;Rossenu et al, 2003;Domanski et al, 2004). Given their repeated structures, tetraThymosin␤, Drosophila ciboulot, and the amoebal protein actobindin (harboring four, three, and two repeats, respectively; Lambooy and Korn, 1986;Van Troys et al, 1999;Boquet et al, 2000) form a novel subset of ␤-thymosins. Both ciboulot and actobindin have been demonstrated to display a similar promotive effect on filament growth as is observed Article published online ahead of print.…”

“…Article and publication date are available at www.molbiolcell.org/cgi/doi/10.1091/mbc. E04 -03-0225. for profilin (Boquet et al, 2000;Hertzog et al, 2002). Indeed, profilin serves as a polymerization catalyst by capturing an actin monomer and ushering the actin onto the growing filament barbed end as a 1:1 profilin:actin complex, whereupon profilin itself is released (Pantaloni and Carlier, 1993;Kang et al, 1999).…”

“…Indeed, profilin serves as a polymerization catalyst by capturing an actin monomer and ushering the actin onto the growing filament barbed end as a 1:1 profilin:actin complex, whereupon profilin itself is released (Pantaloni and Carlier, 1993;Kang et al, 1999). Ciboulot is suggested to act on elongation via the same mechanism as profilin by forming a 1:1 complex with an actin monomer (Boquet et al, 2000). The complex of the first domain of ciboulot and monomeric actin have very recently been crystallized .…”

The β‐thymosins: Intracellular and extracellular activities of a versatile actin binding protein family

“…Although WH2-domains from different proteins may share only 15% sequence identity, their common feature is their ability to bind to the barbed-end face of actin. Meanwhile WH2-domains were discovered in about 38 other proteins [see also Hertzog et al, 2004], mainly actin binding proteins, which regulate the organization of the actin cytoskeleton like actobindin possessing two b-thymosin-repeats each containing a WH2-domain [Vancompernolle et al, 1991], ciboulot-a protein with three b-thymosin-repeats found in Drosophila [Boquet et al, 2000], and the nucleating protein Spire, which was first discovered in Drosophila containing four WH2-domains in series [Quinlan et al, 2005]. In contrast to b-thymosins, most of these proteins (such as actobindin, ciboulot, and Spire) support actin polymerization.…”