A major focus of current research in my lab is aimed at understanding mechanisms that control axon outgrowth and guidance. Our goal is to understand how guidance signals function to control axon motility and behavior in the complex in vivo environment, where axons must integrate multiple cues. We use zebrafish embryos as a model system, which allows us to combine molecular/genetic manipulations with live imaging of cell behavior and molecular activity in living intact embryos. In the past several years we have identified multiple molecular signals that guide axons in vivo and have shown how these signals function to control axon motile behavior, growth and direction in several regions of the CNS. One of the neuron types we study, the spinal sensory Rohon-Beard (RB) neurons, make an excellent model to investigate guidance mechanisms because they have stereotyped axon arbor morphology and can be readily imaged in vivo.
A main goal of our recent and current research is to further investigate the molecular mechanisms underlying differential guidance of central versus peripheral RB axons. We are exploring the roles of LIM homeodomain transcription factors in regulating RB morphology and axon trajectory. Inhibition of islet family LIM transcription factors by expression of a dominant negative form of a required cofactor (DN-CLIM) causes a strong reduction or elimination of RB and trigeminal peripheral axons. However, the cell bodies and central axons develop normally, indicating that LIM transcription factors function specifically to control peripheral sensory axon outgrowth. Although transcription factors have been shown in several systems to have key functions in defining axon trajectories, the molecular steps between transcriptional regulation and control of axon motility and morphology remain largely unknown. We have taken two general approaches to defining these molecular steps: 1) We are using live imaging of axon behavior and molecular activity to determine which cell motility processes are affected by DN-CLIM; and 2) We have done a microarray gene expression analysis to identify downstream targets of LIM transcription factors. We have recently published a manuscript characterizing motile behaviors of axons and dynamics of F-actin accumulation in DN-CLIM embryos. Other highlights of the past year are promising results analyzing the function of several genes found in our microarray.
Another main research area in the lab is aimed at understanding mechanisms of neural crest cell (NCC) migration, and in particular the epithelial to mesenchymal transition (EMT) that NCCs undergo to delaminate from the neuroepithelium and begin migration. EMT is a dramatic process involving major changes in cell morphology and motility that allow cell migration and formation of new tissues. EMTs are important for many developmental processes, and are also co-opted in several pathological processes, including cancer metastasis. The mechanisms controlling cell changes during EMT remain poorly understood. Because a cell’s environment strongly influences its motility and intracellular signaling, it is extremely useful to have a model in which we can study these mechanisms while cells undergo EMT in the natural 3D environment. We are again taking advantage of the zebrafish model to combine in vivo imaging of NCC behavior during EMT with manipulation of potential signaling molecules. This year we received an exploratory R21 grant from NIH to develop this system as a means to examine the function and activity of RhoGTPases in controlling cell behavior in an in vivo EMT model.
Zoology 555: Laboratory in Developmental Biology
Neuroscience 765: Developmental Neuroscience
Matt Clay, (email@example.com)
Cell and Molecular Biology PhD student
Tristan Lee, (firstname.lastname@example.org)
Neuroscience Training Program PhD student
Olga Ponomareva, (email@example.com)
Neuroscience Training Program and and Medical Scientist Training Program MD/PhD student.
Erica Andersen, PhD Genetics
Namrata Asuri, PhD Genetics