John Flanagan, PhD
Department of Cell Biology, Harvard Medical School
Molecular analysis of axon guidance
Investigate molecular mechanisms of axonal guidance, including the continuum of axon response to guidance cues, and the corresponding receptor-mediated signaling.
Investigate mechanisms of axonal guidance for developing new approaches to promoting neuronal cell regeneration
Dr. Flanagan has made key discoveries relating to axonal guidance molecules and their mechanism of action. These developmental studies are important for understanding the intricacies of neuronal cell circuitry and the growth and inhibitory mechanisms that control neural topography. Moreover, the insights developed from these investigations will be critical in approaching the formidable task of regenerating neuronal networks damaged in pathological conditions such as spinal cord injury or stroke.
These debilitating disorders have been virtually intractable from the standpoint of effective intervention, due to the inability to effect neuronal regeneration. Clearly, a more fundamental understanding of axonal cell growth, development, guidance, and patterning are needed for future efforts directed at repairing damage to the central nervous system, and Dr. Flanagan’s lab is making important strides in this area. As such, his lab is an attractive partner for companies focused on new paradigms for restoring activity to non-functional regions of the central nervous system via pharmaceutical treatment.
Current Research Interests
Dr. Flanagan’s studies are focused on understanding the molecular basis for the development of the neural wiring patterns, which is highly regulated. For example, axons acknowledge intermediate targets such that their response to guidance cues can be altered. Thus, spatiotemporal aspects of axon guidance are important for deconstructing the molecular events and cell-cell interactions that underlie the development of neuronal connections.
Dr. Flanagan is combining molecular tagging techniques such as Receptor Affinity Probe methodology with cellular and animal models in order to gain insights into the signaling mechanisms that rely on different “beacons” to modulate axon guidance. These beacons, such as the secreted ephrins, signal through cell surface receptor tyrosine kinases, and Dr. Flanagan is investigating the biochemical pathways in neuronal cells that respond to these extracellular cues.
These studies have thus progressed from the identification of different receptor ligands that regulate axonal extensions and neuronal connections, to the current focus on molecular mechanisms that detect the changing gradients of axonal guidance molecules during neural development as well as neural mapping, which describes a topography related to gradient-driven axonal guidance.
Dr. Flanagan has been interested in neuronal signaling processes that mediate axonal guidance, with a particular emphasis on the ephrins, a family of ligands that bind a subclass of transmembrane receptor tyrosine kinases designated as the ephrin receptors. Dr. Flanagan was responsible for identifying one of the ligands to the ephrin receptors, using the powerful technique of Receptor Affinity Probe. This methodology was based on the construction of soluble fusion proteins consisting of the orphan receptor extracellular domain fused to alkaline phosphatase, which enabled coimmunoprecipitation experiments to be performed. These studies helped lay the foundation for investigation into neuronal connectivity and axonal guidance, since ephrin receptors and their ligands play important roles in the development and mapping of neurons in various locations within the central nervous system, including the eye. More recent studies by the lab have focused on the molecular mechanisms of axonal guidance and neural mapping. Employing reporter genes, the lab demonstrated that local protein synthesis occurs within axons, and can lead to membrane targeting of newly synthesized proteins. Importantly, the ephrin A2 receptor was found to contain regulatory elements in its 3’ mRNA untranslated region that help mediate this regulation.
Other studies from the lab have addressed the complex and diverse neural mapping patterns that correlate with different functional systems, such as the visual and olfactory networks. These mapping studies are attempting to draw a unified functional picture of axon guidance and neural wiring.