The Actin-Binding Protein UNC-115/abLIM Controls Formation of Lamellipodia and Filopodia and Neuronal Morphogenesis in Caenorhabditis elegans

Abstract

The roles of actin-binding proteins in development and morphogenesis are not well understood. The actin-binding protein UNC-115 has been implicated in cytoskeletal signaling downstream of Rac in Caenorhabditis elegans axon pathfinding, but the cellular role of UNC-115 in this process remains undefined. Here we report that UNC-115 overactivity in C. elegans neurons promotes the formation of neurites and lamellipodial and filopodial extensions similar to those induced by activated Rac and normally found in C. elegans growth cones. We show that UNC-115 activity in neuronal morphogenesis is enhanced by two molecular mechanisms: when ectopically driven to the plasma membrane by the myristoylation sequence of c-Src, and by mutation of a putative serine phosphorylation site in the actin-binding domain of UNC-115. In support of the hypothesis that UNC-115 modulates actin cytoskeletal organization, we show that UNC-115 activity in serum-starved NIH 3T3 fibroblasts results in the formation of lamellipodia and filopodia. We conclude that UNC-115 is a novel regulator of the formation of lamellipodia and filopodia in neurons, possibly in the growth cone during axon pathfinding.

ACKNOWLEDGMENTS

We thank M. Buechner, K. Neufeld, R. Ward, and members of the Lundquist lab for critical reading of the manuscript and discussions; K. Neufeld, S. Quackenbush, and J. Rovnak for assistance with cell culture and transfection; E. Struckhoff and S. Mariano for technical assistance; and A. Fire for gfp vectors.

Some C. elegans strains used in this work were provided by the C. elegans Genetics Center, funded by the National Center for Research Resources. This work was supported by NIH grant NS40945 and NSF grant IBN93192 to E.A.L.