Research Description
Mechanisms of Axon Guidance in Zebrafish
My research is aimed at understanding how axons are guided to their targets during development of the nervous system. Several families of molecules have been identified that can act as axon guidance molecules by either attracting or repelling the motile growth cone at the tip of the growing axon. I am studying one class of molecules, called semaphorins, that were originally identified as inhibitory axon guidance molecules. The semaphorin gene family is very large and diverse, and is highly conserved from invertebrates to humans. To date little is known about how most family members function in vivo to affect growth cone motility and guide the direction of axon growth.
I use the zebrafish as an animal model to analyze semaphorin function in vivo. The zebrafish is a simple vertebrate with rapidly developing, transparent embryos ideal for visualizing developing axons. My goal is to combine the manipulation of gene expression with live imaging of growing axons to determine how semaphorins function in neural development. I have generated transgenic zebrafish in which I can misexpress semaphorin genes and analyze effects on growing axons. In these fish, the semaphorin transgene is driven by an inducible heat shock promoter. By heating embryos, we can turn on ectopic semaphorin expression throughout the embryo at select developmental time points. In addition, we can use a laser microbeam to heat individual cells and turn on the transgene in any cell of the embryo. We then use time lapse microscopy to observe behaviors of living growth cones when they encounter semaphorin expressing cells within the embryo. In addition, we can block expression of semaphorins with morpholino antisense. By analyzing the activity of semaphorins on living growth cones in vivo, I hope to reveal how these molecules normally function in vivo to control the formation of neural connections.
Recent Publications
Halloran, M.C., Sato-Maeda, M., Warren, J.T. Jr., Su, F., Lele, Z., Krone, P.H., Kuwada, J.Y., and Shoji, W. (2000) Laser-induced gene expression in specific cells of transgenic zebrafish. Development 127:1953-1960..
Halloran, M.C., Severance, S.M., Yee, C.S., Gemza, D.L., Raper, J.A., and Kuwada, J.Y. (1999) Analysis of a zebrafish semaphorin reveals potential function in vivo. Dev. Dynamics 214:13-25.
Halloran, M.C., Severance, S.M., Yee, C.S., Gemza, D.L., and Kuwada, J.Y. (1998) Molecular cloning and expression of two novel zebrafish semaphorins. Mech. Devel. 76:165-168.
|
