Sci. STKE, 6 August 2002
Axon Guidance EphrinB-EphB Create a Dorsoventral Map
How neurons find their proper targets and spatial position is an intriguing question. Two groups analyzed how the dorsoventral mapping of the retinal axons onto the optic tectum is achieved in the frog, Xenopus laevis (Mann et al.), and mouse (Hindges et al.). Mann et al. show that the expression of Ephrin B ligands and EphB receptors is complementary, with Ephrin B high in the dorsal area and EphB high in the ventral area. In vivo and in vitro experiments support a role for Ephrin B-EphB in mediating an attractive response and for reverse signaling through the Ephrin B-expressing cells in mapping the Xenopus visual system. Hindges et al. show that in mouse, there are also complementary gradients of Ephrin B and EphB. This group used mice carrying deletions or mutant forms of EphB2 and EphB3, and their results are consistent with forward signaling through these receptors being important for proper organization of the axonal projections onto the optic tectum. It remains to be determined whether both systems (mouse and frog, and presumably other species, including humans) use forward signaling through the EphB receptor and reverse signaling through the Ephrin B receptor to complete the topographic map of the retinotectal system. Another question that needs to be resolved is how these signals are interpreted to yield either attraction or repulsion depending on the stage of development or position along the axon projection pathway (see Pittman and Chien). For more information on the forward and reverse signaling by Ephrin-Eph interactions, see Boyd and Lackmann.
F. Mann, S. Ray, W. A. Harris, C. E. Holt, Topographic mapping in dorsoventral axis of the Xenopus retinotectal system depends on signaling through Ephrin-B ligands. Neuron 35, 461-473 (2002). [Online Journal]
R. Hindges, T. McLaughlin, N. Genoud, M. Henkemyer, D. D. M. O'Leary, EphB forward signaling controls directional branch extension and arborization required for dorsal-ventral retinotopic mapping. Neuron 35, 475-487 (2002). [Online Journal]
A. J. Pittman, C.-B. Chien, Understanding dorsoventral topography: Backwards and forwards. Neuron 35, 409-414 (2002). [Online Journal]
A. W. Boyd, M. Lackmann, Signals from Eph and Ephrin proteins: A developmental tool kit. Science's STKE (2001), http://stke.sciencemag.org/cgi/content/full/OC_sigtrans;2001/112/re20. [Abstract] [Full Text]
Citation: EphrinB-EphB Create a Dorsoventral Map. Sci. STKE 2002, tw292 (2002).
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