The Journal of Neuroscience, May 1, 2002, 22(9):3615-3627
Protein Tyrosine Phosphatase-µ Differentially Regulates Neurite
Outgrowth of Nasal and Temporal Neurons in the Retina
Susan M.
Burden-Gulley,
Sonya E.
Ensslen, and
Susann M.
Brady-Kalnay
Department of Molecular Biology and Microbiology and Department of
Neurosciences, School of Medicine, Case Western Reserve University,
Cleveland, Ohio 44106-4960
Cell adhesion molecules play an important role in the development
of the visual system. The receptor-type protein tyrosine phosphatase,
PTPµ, is a cell adhesion molecule that mediates cell aggregation and
may signal in response to adhesion. PTPµ is expressed in the chick
retina during development and promotes neurite outgrowth from retinal
ganglion cell (RGC) axons in vitro (Burden-Gulley and
Brady-Kalnay, 1999). The axons of RGC neurons form the optic nerve,
which is the sole output from the retina to the optic tectum in the
chick. In this study, we observed that PTPµ expression in RGC axons
occurs as a step gradient, with temporal axons expressing the highest
level of PTPµ. PTPµ expression in the optic tectum occurred as a
smooth descending gradient from anterior to posterior regions during
development. Because temporal RGC axons innervate anterior tectal
regions, PTPµ may regulate the formation of topographic projections
to the tectum. In agreement with this hypothesis, a differential
response of RGC neurites to a PTPµ substrate was also observed: RGCs
of temporal retina were unable to extend neurites on PTPµ compared
with neurites of nasal retina. When given a choice between PTPµ and a
second substrate, the growth cones of temporal neurites clustered at
the PTPµ border and stalled, thus avoiding additional growth on the
PTPµ substrate. In contrast, PTPµ was permissive for growth of
nasal neurites. Finally, application of soluble PTPµ to retinal
cultures resulted in the collapse of temporal but not nasal growth
cones. Therefore, PTPµ may specifically signal to temporal RGC axons
to cease their forward growth after reaching the anterior tectum, thus
allowing for subsequent innervation of deeper tectal layers.
Key words:
neurite outgrowth; protein tyrosine phosphatase; cell
adhesion; retina; tectum; pathfinding
Copyright © 2002 Society for Neuroscience 0270-6474/02/2293615-13$05.00/0