Intracellular Signaling During Midline Guidance in Drosophila

Wayne State University, Detroit MI

Investigators

Abstract

0091478 During development, neurons extend axons along very specific pathways to their target cells. Steering decisions are made as surface receptors at the tip of the axon (the growth cone) detect molecular guidance cues and convert them into intracellular signals that regulate growth cone movement. The long-term goal of this work is to understand how intracellular signaling pathways orchestrate the motile response underlying guidance decisions. The development of the embryonic nerve cord of Drosophila provides a unique opportunity to identify these intracellular signaling pathways. The ladder-like axon scaffold of the fly embryo is formed as axons decipher attractive and repulsive cues that dictate which axons may cross the midline. Several of the genes involved in this decision have been identified including three key intracellular signaling molecules: Calmodulin, Son-of-Sevenless (Sos) and Profilin. Interestingly, each of these molecules regulates key aspects of actin and myosin dynamics underlying motility. Thus it is hypothesized that a growth cone's response to midline guidance cues is tightly linked to its ability to regulate actin and myosin dynamics. To test this hypothesis, Dr. Van Berkum will define the role of downstream targets of both Calmodulin and Sos which may regulate actin and/or myosin processes during a midline guidance decision. Specifically, Dr. Van Berkums's work will focus on Myosin Light Chain Kinase, a target of Calmodulin, and three monomeric GTPases (Rac, Rho and Cdc42) known to function downstream of Sos. To investigate the role of Profilin, each of the three functional domains of Profilin will be neutralized by selected point mutations in order to determine which domain of Profilin is required to cross talk with Calmodulin dependent processes during axon guidance. In all cases, proteins are expressed in the developing embryo and midline guidance choices assayed by antibody staining. Given the essential role of Profilin, Sos and CaM as regulators of actin and myosin dynamics, this work will provide insight into how axon pathways, and thus nerve connections, are formed. Similar mechanisms will undoubtedly be used to regulate cell motility and/or contraction in a variety of other cell types.