Journal of Neuroscience, Vol 16, 2074-2085, Copyright © 1996 by Society for Neuroscience
Cellular localization of guidance cues in the establishment of retinotectal topography
RW Davenport, E Thies and PG Nelson
Laboratory of Developmental Neurobiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
Topographic projections of the nervous system are essential to numerous
brain functions. They arise during development as a result of encounters
between projecting growth cones and particular target cells. Cellular
localization of guidance cues can indicate the sequential processes
involved in establishment of such topography. The map formed by retinal
ganglion cells on their target nuclei has served widely as a model system
to investigate mechanisms underlying the highly precise and stereotypic
connectivity of the nervous system. To investigate cellular localization of
guidance cues in the developing retinotectal system, a three-compartment
chamber was created to delimit areas where cultured embryonic chick retinal
ganglion axons and tectal cells encounter one another and guidance behavior
could be readily assessed. Whereas explants from nasal retinae extended
fibers across their natural target population, fibers from temporal regions
of retinae failed to invade areas of growing posterior tectal cells. This
preservation of relevant guidance information on living cell populations
enabled an evaluation of retinal ganglion cell growth cone behavior after
encounter with individual tectal cells. Posterior tectal neurons appeared
selectively repulsive for temporal retinal ganglion cell growth cones,
causing growth cone collapse and retraction. On the contrary,
neuroepithelial cells from all regions of the tectum attenuated retinal
ganglion axon extension, without inducing sudden retraction. Nasal growth
cones traversed or tracked more often along neuroepithelial cells from
their natural target area, potentially indicating a second set of guidance
cues possibly localized to posterior glia. Together, these differential
interactions suggest that development of retinotectal topography critically
depends on cell- specific cues, which are distributed selectively on
particular populations of target cells.
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