The Journal of Neuroscience, July 1, 1998, 18(13):5008-5018
Differential Withdrawal of Retinal Axons Induced by a
Secreted Factor
Hiroyuki
Ichijo1, 2 and
Friedrich
Bonhoeffer2
1 Department of Anatomy, Institute of Basic Medical
Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan, and
2 Max-Planck-Institut fuer Entwicklungsbiologie, Abteilung
Physikalische Biologie, 72076 Tuebingen, Germany
To understand the development of the topographic map in the chick
retinotectal projection, we studied the long-term interactions between
retinal axons and tectal cell processes using a novel coculture system,
the ryomen chamber. Both nasal and temporal retinal
axons initially grew equally well on a substrate consisting of
posterior tectal cell processes; however, subsequently most temporal
axons withdrew from this surface, whereas most nasal axons did not.
Experiments using conditioned media indicate that posterior tectal
cells induced withdrawal of the temporal axons by secreting a soluble
factor. This withdrawal seems to be distinct from the immediate
repulsive effect of ephrin-A2 (ELF-1) and ephrin-A5 (RAGS) seen in the
stripe assay because (1) the withdrawal-inducing factor was diffusible,
whereas ephrin-A2 and -A5 are membrane-bound, and (2) the
withdrawal-inducing factor appeared later in development than ephrin-A2
and -A5. Furthermore, sensitivity to the withdrawal-inducing factor
decreased continuously from the temporal to nasal retina. These results
suggest that target cell-induced axonal withdrawal may be involved
during a late stage of the development of the retinotectal map.
Key words:
axon guidance; retinotectal projection; topographic map; remodeling; chick embryo; neural development; repulsive factors
Copyright © 1998 Society for Neuroscience 0270-6474/98/18135008-11$05.00/0