During neural development motile growth cones at the leading edge of elongating axons and dendrites use environmental cues to navigate to their synaptic targets. While many diffusible, cell surface and extracellular matrix bound guidance cues and their receptors have been identified, relatively little is known of the downstream intracellular signal transduction cascades they activate. One intracellular signal that has particularly diverse effects on axonal and dendritic growth is cytosolic calcium ions (Ca2+). Transient elevations of intracellular Ca2+ in growth cones can promote, inhibit or orient motility depending on the size, duration and distribution of these signals, as well as on the downstream Ca2+-dependent targets available. Interestingly, the mode of Ca2+ entry has also been found to determine the specificity of some responses. The diverse effects of Ca2+ on neurite outgrowth are likely due to the many cytoskeletal regulatory targets expressed by growth cones. Importantly, recent evidence suggests that Ca2+ signaling may influence the activity of some of the Rho-family of small G proteins. Rho-family GTPases are potent and diverse regulators of the actin cytoskeleton in growth cones and could be key intermediaries between Ca2+ signals and growth cone motility. Dr. Gomez hypothesizes that Ca2+ influx through plasma membrane channels versus release from intracellular receptor stores regulate distinct subsets of Ca2+-sensors within local microdomains of growth cones. Further, the downstream signaling pathways activated by Ca2+ movement through different channels will have opposing effects on growth cone motility. The aim of this study is to begin by characterizing the effects of altering general and specific Ca2+ influx and release pathways on neurite outgrowth. Next, the effects of these Ca2+ changes on the activity of three different Rho GTPases will be measured and the necessity of GTPase function for motility determined. The long-term goal of Dr. Gomez's research is to understand how specific Ca2+ signals orchestrate the spatial and temporal activation of downstream targets that control growth cone pathfinding. Knowing the molecular mechanisms through which Ca2+ exerts such varied effects on growth cone motility will support treatment strategies for developmental disorders and neural injury. Five graduate students from three different graduate programs and two undergraduates are current members of the Gomez Lab. The proposed project will directly involve two graduate students, but all students will receive some indirect support from this award. Students in the lab are trained as developmental neurobiologists using molecular and biophotonic based approaches. Student participation in research, as well as coursework, journal clubs, lab meetings, graduate program subgroup meetings, and international meetings reflect this focus. In addition to receiving training, graduate students are expected to teach junior graduate students, undergraduates or in some cases high school students. Several students are currently involved in University organized teaching programs. Dr. Gomez is also an active member of the Carnegie Initiative on the Doctorate (CID) planning committee. If awarded to the Neuroscience Training Program, CID will be a multi-year research program aimed at enriching and invigorating the education of doctoral students. Finally, as a member of the Biophotonics cluster hire, Dr. Gomez collaborates with labs in other departments such as Physiology and Electrical and Computer Engineering. These collaborations focus on technology transfer and as indicated by this agreement the Gomez lab provides imaging expertise as well as access to the lab's modern imaging facilities.
