UC San Diego

Actin capping protein (CP) binds to the barbed ends of actin filaments and inhibits further polymerization. CP is thought to be essential for cell motility, but its role in mammalian migration has not been directly tested. Moreover, CP is widely believed to be absent from filopodia, and a role for CP in filopodia has remained uninvestigated. I have explored the role of CP in migrating cells and in primary hippocampal neurons. I begin this dissertation by reviewing the relevant literature on CP and on filopodia (Chapter One). I then investigate the effects of silencing CP in migrating B16F10 melanoma cells (Chapter Two). I find that depleting CP impairs cell migration. Moreover, CP is unexpectedly detected in filopodia, and CP depletion has dramatic effects on filopodial morphology and dynamics.These effects may be mediated by unchecked actin polymerization resulting from severely reduced capping activity and consequent depletion of monomeric actin. My novel findings suggest that CP may be an important player in filopodial form and function. I also report that silencing CP has dramatic effects on neuronal development (Chapter Three). CP depletion in primary hippocampal neurons accelerates neuronal maturation in vitro without affecting neurite length or number of Stage III neurons; these effects may possibly be mediated by changes in filopodial number. Finally, I outline the outstanding questions raised by my results in Chapters Two and Three and discuss future experiments that could help to address these questions (Chapter Four)